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Chapter 14 Health management.

All horse owners want their horses to be healthy, to look good, and to be physically fit. Most have a sense that these three things are connected. But in what ways? How can an owner or trainer tell whether a horse is healthy just by looking at it? What does a healthy horse look like? And, once the state of a horse's health is determined, what can be done to improve and maintain it? These are good questions. The problem is that almost every horse owner would answer them differently.


After completing this chapter, you should be able to:

* Define terms associated with disease conditions

* Discuss disease resistance and immunity

* Define terms associated with the severity of a disease or condition

* Describe immunization

* Discuss how a vaccination program relates to immunity

* List signs of disease

* Discuss common diseases caused by viruses

* Discuss common diseases caused by bacteria

* List five noninfectious diseases

* Describe the signs of good health in a horse

* List the objectives for first aid for horses

* List four digestive diseases

* List five respiratory diseases

* Discuss laminitis and colic

* Relate body condition to health


active immunity





capillary refill

condition score







passive immunity

passive transfer





For the horse owner or anyone working with horses, the first step in health management is learning to recognize a healthy horse. Disease can then be recognized and treated early.

Healthy horses show good body condition. Other ways to quickly assess the health of a horse include evaluating its general appearance and behavior, examining specific parts of the body (such as hoofs and eyes), observing its manure and urine, and measuring vital signs such as heart rate, respiratory rate, and temperature.

Normal Body Condition

Body condition refers to the amount of fat cover on horses. A scoring system that assesses fat cover has been designed to gauge reproductive efficiency in mares. An evaluation--or condition score--based on this system can also serve as a guide to judging the nutritional status of all horses. This system is presented in Table 14-1.

Most horses should score between 4 and 6. Scores lower than 4 or higher than 6 on this scale could indicate metabolic and other health problems.

When using the scoring system, the following factors need to be considered:

1. Accuracy will increase if the areas of fat accumulation can be palpated.

2. Long hair may mask the appearance of fat.

3. Different body conformations affect the ability to visually determine body condition.

4. Taller, larger-framed horses with prominent withers may appear to be leaner than shorter, smaller-framed horses with similar body conditions.

5. Mares in late gestation may have less fat cover over the ribs due to the influence of the weight of the fetus and associated tissues. More emphasis should be placed on other locations of fat accumulation.

6. Horses on high-percentage forage diets will typically have larger bellies with lower, distended abdomens than will horses being managed on grain or in exercise programs. These "hay bellies" can give the appearance of fat, causing overestimation of body condition.

7. Periodic reevaluations of individual horses will help to decrease the influence of conformational differences in body condition assessment.

Body condition cannot be altered significantly in short periods of time. Gains in body weight must be made with gradual increases in the ration. The horse's body requires time to assimilate increases of energy into fat. Also, the incidence of colic and founder will increase when making dramatic adjustments in the amount of the daily ration. Increasing a mature horse's body condition from a score of 3 to a score of 6 may take up to 4 months when consuming about 1.75 percent of body weight in grain per day and unlimited hay.

Other Signs of Good Health

Observing horses at horse events like shows, races, and other competitions is another good way to establish a standard for what is normal.

A bright, actively interested horse can be recognized at a glance (Figure 14-1). It will be alert, inquisitive, and attentive. It will not have the dull, lethargic look that can indicate over-training, overuse, or ill health.

When in pastures, lots, and paddocks, horses normally will try to stay in a group, so one off by itself may be hurt or ill. Normal, healthy horses also chew evenly with both sides of their mouth and show predictable enthusiasm for eating.

A shiny, glossy hair coat is one of the best indicators of a healthy horse. Hair coat reflects good nutrition and health and certainly can be improved by regular grooming.

Hair Coat. Normal, healthy horses have healthy hoof-wall tissue. The wall should grow at a rate of 14 to 12 inch per month. The hoof should be smooth and uncracked, forming a straight line with the front of the pastern when viewed from the side.


Eyes. The eyes should be bright, fully open, and clear, without discharge or a glazed, dull appearance.

Hydration. The water balance of a horse is vital to its health. A skin-fold test can be done by pinching a fold of skin on the neck, pulling it out, and recording the number of seconds the skin takes to return to its normal position. One-half to 1 second is normal; longer means the horse is dehydrated.

Manure/Urine. Horses normally have firm manure balls that are not loose and watery and do not show undigested grains and other feedstuffs. Urine is normally wheat-straw colored and not cloudy or dark red.

Mucous Membranes. The membranes of the horse's gums and lips should be a healthy pink. Pale, white, yellow, or deep purple colors are all cause for concern.

Capillary Refill. A horse's circulation can be assessed by gently pressing a thumb against the gums of the horse and counting the number of seconds it takes for the color to return to the area once the thumb is removed. One to 2 seconds is normal.

Heart Rate. The normal heart rate of an adult, resting horse is 32 to 48 beats per minute. This will vary with the age of the horse, ambient temperature and humidity, exercise, and excitement levels.

Respiratory Rate. The normal respiratory rate of an adult, resting horse is 8 to 16 breaths per minute. Exercise, ambient temperature, humidity, fever, distress, pain, and anxiety will increase the respiratory rate.

Temperature. The normal body temperature of a horse is 99.5[degrees]F to 101.5[degrees]F. High environmental temperature, exercise, or dehydration can increase this by 2 to 3 degrees (Table 14-2).

Body Weight

Regardless of body type and breed, the nutritional requirements, medical dosages, and management practices vital to maintaining healthy horses are based on body weight.

This is one area where observation, no matter how close, is not sufficient. The only way to get an accurate, reliable weight for a horse is to weigh it. It is important to realize, however, that a horse's weight can vary by as much as 60 pounds, depending on how recently it has eaten, drunk, urinated, and defecated.

Overweight horses are more common than malnourished ones, but the health of the horse is compromised in either case. Health management begins with proper feeding to meet the horse's nutritional needs and keep it in top physical condition.


The nutritional requirements of horses depend on their exercise level, reproductive state, age and growth rate, and mature body weight. These must be determined in order to feed horses properly. Determinations must be based on the actual use and condition of each horse, not on good intentions or wishful thinking by the owner. Each horse is different and needs to be fed according to its individual temperament, metabolic rate, and genetic makeup (Figure 14-2).


Feeding Classification

Nutritional requirements and proper feeding of horses were covered in Chapters 12 and 13. The basic feeding classifications to ensure good health include maintenance, pregnancy, lactation, growth, and work.

Maintenance. The horse in this feeding classification is mature, maintaining its body weight. It is not pregnant, lactating, breeding, or being exercised. The nutritional requirements are very low relative to other classifications.

Pregnancy. Nutritional requirements during the first 8 months of pregnancy are the same as for a mare being maintained. However, during the 9th, 10th, and 11th months of pregnancy, the mare's requirements increase 11 percent, 13 percent, and 20 percent, respectively.

Lactation. During the first 3 months after foaling, mares can produce milk equivalent to 3 percent of their body weight every day and 2 percent per day during months 4 to 6. Feeding requirements are about 70 percent above maintenance during the first 3 months of lactation and 50 percent during months 4 to 6.

Growth. Growing foals require feeds of higher quality than those for maintenance. Growth rate and age of the foal determine the requirements. Horses are considered to be growing for up to 30 months, and for longer in the slower-maturing breeds. Optimum growth rates for various breeds have not been well defined; but overfeeding can cause developmental orthopedic diseases, and underfeeding can cause permanent stunting (Figure 14-3).

Work. Horses being exercised or worked require more nutrients, especially energy, than do horses being maintained. As the intensity or duration of the work increases from light to moderate to intense, energy requirements increase 25 percent, 50 percent, and 100 percent above maintenance, respectively.


Essential Nutrients

Horses need the same basic nutrients that humans do: water, energy, protein, minerals, and vitamins. In horses, as in humans, too much or too little of any of these essentials can lead to serious health problems.

Water. Horses need a good supply of clean water daily. Water is essential for all body functions, including temperature regulation and feed digestion. The amount of water needed depends on exercise level, ambient temperature, quality of the feeds in the ration, and proportion of the diet that is forage. A minimum of 1 gallon of water per 100 pounds of body weight per day should be provided.

Energy. The nutrients in a horse's rations primarily determine its weight and condition. Energy is derived primarily from carbohydrates, fats, and any protein excesses. Energy is needed for body functions, including maintenance, temperature regulation, digestion, and work. All energy provided beyond what the body needs goes toward the formation of fat. A deficiency of energy will reduce the body condition score (fat) before the biological needs will be sacrificed. Prolonged deficiencies will result in unthriftiness and starvation. Excesses of energy can cause obesity, which can in turn cause many metabolic diseases such as laminitis (founder), osteochondrosis, epiphysitis, tying-up syndrome, and colic.

Protein. The body needs proteins for muscle and bone growth, milk production, fetal growth, and normal metabolism. Protein requirements of many horses, especially those in the maintenance, early pregnancy, and exercise classifications, can be met with good-quality hay or pasture forage.

Minerals. The development of bone and many essential reactions within the body require adequate levels of calcium, phosphorus, sodium, chloride, selenium, and other minerals. Many of these minerals can be adequately supplied with good-quality mixed hays or a mineral supplement in the concentrate mixture. Trace-mineralized salt with selenium should always be available.

Vitamins. Fat-soluble vitamins (A, D, E, and K) as well as water-soluble vitamins (B complex and possibly C) are required as coenzymes throughout the body for normal metabolism. Because forages are rich sources of vitamins, very few horses grazing good pastures or fed predominantly good hay are likely to need supplementation. High-stress situations may require vitamin B complex supplementation.


Keeping a horse healthy requires diligent attention to details. But prevention is always better than treatment.

General Program

Following are a few minimum guidelines essential for normal horse care. Horses vary widely in their metabolism and must be managed as individuals in regard to maintaining health. For more specific guidance and when questions arise or problems develop, owners should seek help from a veterinarian, extension agent, farrier, feed store operator, or some other equine professional.

1. Shelter from wind and weather with trees and a shed or barn is adequate in most climates. Much of the tradition about horse housing is for the owner's comfort, not the horse's.

2. To reduce chance of injury, a safe environment that is free of hazards such as nails, barbed wire, broken fences, glass windows, and unsecured pesticides should be provided.

3. Adequate clean water should be provided at least two times a day; free access to water is best.

4. A routine schedule of feeding and exercise should be maintained. Sudden changes in feeds, feeding schedule, or work/activity can cause lameness, colic, and muscle problems. Regular exercise, either free-choice or regulated, is important in maintaining athletic horses.

5. Horses are natural nibblers. They can be fed once a day but will be more efficient (digest more of their feed) if fed two or three times daily.

6. Horses should be fed at least 1.5 to 2.5 percent of their body weight per day in hay or pasture. Hay (forage) helps prevent intestinal problems and abnormal behavior (vices) caused by lack of fiber and boredom.

7. Commercial concentrate feed mixtures should be used if necessary to supply the nutrients needed. The concentrate should be selected to complement the hay or pasture composition. Feed should be fed based on weight, not volume.

8. Hays and feeds should be free of dust and mold.

9. When necessary, feeds should be changed gradually over a 10- to 14-day period.

10. Floating (filing) a horse's molars to decrease the sharp points that interfere with normal chewing is often needed. Regular dental checkups and floating will prevent mouth problems.

11. Horses should be dewormed regularly, and parasite load should be assessed with occasional fecal floatation tests and treated accordingly.

12. All horses should be on a regular vaccination schedule that includes tetanus.

13. Regular hoof care is important. Feet may need to be trimmed periodically if hoof growth exceeds wear, but it is not usually necessary to keep shoes on horses that are not in training or being ridden or driven on rough terrains.


The immune system forms the body's defense against a foreign substance, whether microorganisms (bacteria, fungi, viruses, protozoa, and parasites), a potentially toxic material (foreign protein, carbohydrate, or nucleic acid), or an abnormal cell (one invaded by a virus or that has become malignant). It attacks the foreign substance and maintains a memory of the invader so that a second exposure will provoke a greater, faster response.

Immunity refers to the ability of an animal that has recovered from a disease to remain well after a second exposure to the same disease. Immunology is the branch of medicine concerned with the body's response to foreign substances and abnormal cells; immunization is the ability to create a response to fight an illness without exposing the body to that illness.

Under normal circumstances the immune system responds to foreign organisms by producing antibodies and stimulating specialized cells that destroy the organisms or neutralize their toxic products. The immune system monitors the body's cells constantly to ensure that they are not abnormal. Cells infected with viruses or cells from another animal (even the same species) have protein markers on their outer membranes that signal the immune system to destroy them. The immune system also can recognize and eliminate malignant or abnormal cells within the body. These mutant, or cancer, cells may occur spontaneously, or they may be induced by certain viruses or chemicals (mutagens).

Cells and Tissues in the Immune Response

The immune system has two general responses: it activates cells to destroy a harmful cell with cell-to-cell interaction, or it activates other cells to produce large protein molecules called antibodies that bind to bacteria, yeast, some viruses, and even toxins (poison) and make them harmless. In many cases, both responses occur. To activate the immune cells, large cells called macrophages eat and partially digest the invading material and place pieces of it, called the antigen, on its surface (Figure 14-4). This attracts and activates T cells from the thymus.


Since the T cell and the antigen must fit together in order to bind, there are many different T cells to match the many antigens. If the T cells are what are called the helper type, they will attract B cells, formed in the bone marrow, whose receptors must also match the antigen. The combination of antigen prepared by the macrophage and helper T cell will activate the B cell specific for that antigen, which multiplies to form a clone. The clone then begins to make antibodies. Other clonal cells form the immune memory for this antigen by remaining indefinitely in an alert state, ready to multiply again should the antigen appear in the future.

Antibodies control not only bacteria but also viruses, fungi, yeast, parasites, protozoa, and many toxic chemicals. In addition to helper T cells, there are killer T cells that can recognize a body cell that has been invaded by a virus and kill that cell so the virus cannot multiply.

Macrophages found throughout the tissues of the body and in the form of monocytes make up about 3 percent of white blood cells. Lymphocytes, two-thirds of which are T cells and one-third B cells, constitute 30 to 40 percent of white cells of the blood. T cells are also found in the thymus gland and in lymph nodes. B cells make up the cells of the outer portion of lymph nodes.


An antigen is a substance that, when introduced into an organism, induces an immune response consisting of the production of a circulating antibody. This type of immunity is known as humoral immunity. Protein molecules are potent antigens. Within a few days after injection, an antigen summons large amounts of the antibody capable of interacting with it. The interaction of an antigen with its specific antibody does not involve the entire antigen but only small areas on its surface.


The molecules responsible for recognizing antigens on foreign molecules on cell surfaces are called antibodies. Antibodies are members of a related group of gamma globulin molecules known as immunoglobulins (Ig). A typical immunoglobulin is made of four protein chains joined together in two pairs.

Five classes of immunoglobulins exist, based on structural differences. These differences are identified by the Greek letters gamma, mu, alpha, delta, and epsilon, and the immunoglobulins that contain them are called IgG, IgM, IgA, IgD, and IgE, respectively. Each class has different biological and structural properties and is distributed throughout the body.

IgG, the most abundant immunoglobulin, occurs primarily in blood serum as well as throughout the internal body fluids. Produced in response to bacteria, viruses, and fungi that have gained access to the body, IgG is a major line of defense against such organisms.

Antibodies in Defense

The simplest and most prevalent means by which the immune system defends the body against bacteria and viruses is by the combination of a specific antibody with the antigens located on the surface of invading organisms. An aggregate of cells, called an agglutination, is formed by antibodies bound by one of their two combining sites to one cell, and to another cell by their other site. These aggregates are then engulfed and digested by the body's wandering scavenger cells, the macrophages. Antibodies also bind to toxic molecules (toxins) given off by microorganisms, forming large, insoluble aggregates (precipitates) that are also removed by macrophages. Antibodies also cover up the attachment sites of viruses, preventing their ability to infect cells. Precipitin and agglutination reactions are used as diagnostic tools for identifying and quantifying the antibodies of infectious organisms in blood samples and other body fluids.

The Newborn Foal

Because protective antibodies are too large to pass through the mare's thick placenta and into the foal's bloodstream, antibodies are not provided to the foal by the mare during gestation. Immunity for the foal is available only through the antibodies in the mare's first milk, the colostrum. The colostrum, however, is available for only 48 hours, after which it is replaced by normal milk, which has no immunity value. Ingestion of colostrum is the most critical factor influencing the foal's survival, growth, and future health.

The foal's ability to absorb antibodies from the colostrum through the lining of the duodenum of the intestine is based on the presence of special absorption cells in the small intestine. These special cells decrease rapidly over the first 24 hours of the foal's life. After 48 hours they are replaced with normal duodenal lining; a foal can absorb antibodies only during its first 2 days and absorbs most of them within its first 12 hours of life. The foal must receive colostrum during the critical first 12 hours of life to receive the antibodies it will need for immunity in the following 3 to 4 months (Figure 14-5).

Antibodies are passed from mare to foal through passive transfer. Occasionally a foal exhibits a failure of passive transfer; even though the antibodies are readily available in the colostrum, the foal is unable to absorb and use them. An immunoglobulin, IgG, test can be performed to identify failure of passive transfer of blood. An immunoglobulin level of less than 600 to 800 mg/dl (milligrams per deciliter) indicates a problem. Blood IgG levels below 400 mg/dl indicate a failure of passive transfer, and a veterinarian should be consulted.

Antibodies against certain diseases will be present in the mare's colostrum if she is vaccinated with booster injections 30 days before parturition. The mare should be vaccinated against all common diseases, because the colostrum can contain antibodies against only those diseases to which she has been exposed. Tetanus is one disease to which horses are extremely susceptible. If the mare has not been given a tetanus toxoid 30 days prior to parturition, then the foal should be given 1,500 IU of tetanus antitoxin at birth to protect it from the tetanus pathogen, which is ever present in equine feces.


No antibiotics or probiotics, such as special vitamin formulations, should be administered the first day of life in an effort to bolster the foal's vigor. These tend only to increase illness and diarrhea in the newborn foal.

Occasionally a mare does not produce milk in adequate quantities, produces poor-quality colostrum, leaks her colostrum, or dies. A source of frozen colostrum taken from other mares will give the foal the immune protection it needs. Milking 6 to 8 ounces of colostrum from all mares after their foals have suckled will provide a reserve that can be frozen. This resource should be on hand even if no problems are expected. When used, this colostrum should be slowly heated, not microwaved, to body temperature. Microwaving destroys the protein molecules that make the antibodies protective. The best colostrum sources will be from mares on the same farm as the foal in order to provide the most specific immunity. Nurse mares can be used as a source of milk.

Plasma transfusions can be used to raise the IgG levels in foals that are more than 24 hours old. Generally 1 liter of plasma is administered over a 30- to 60-minute period, depending on the foal's vigor. The best plasma source is from a horse living on the same farm as the foal. Commercial plasma sources are available, but the antibodies in this plasma may not be specific enough to give the foal adequate protection against the particular disease organisms in its immediate environment. Typically, a plasma transfusion of 1 liter raises the IgG level only 200 mg/dl. More than one transfusion may be needed for foals with very low IgG levels.

Premature Foals

Foals that arrive prematurely (before 320 days of gestation) are especially susceptible to risks from the environment and disease. Since their bodies are physiologically underdeveloped, they are unprepared, even with sufficient colostrum, to adequately resist disease. The lungs of premature foals are especially underdeveloped. They tend to have low body temperatures; are especially susceptible to colds, infections, and hypothermia; and require intensive care if they are to survive.


Horses establish an immunity to a specific disease first by being exposed and then by developing their own antibodies to fight off that specific disease. A foal is born with no immunity (antibodies of its own), and the protection it first receives must come in the form of colostrum from its dam. This is termed passive immunity--when an animal receives antibodies that were produced by another animal. Active immunity is when an animal is challenged and stimulated to produce its own antibodies. This challenge is usually a disease that is present and introduces a foreign protein or antigen into the animal. If the horse has a high level of antibodies in its blood, the antibody titer (level) is said to be high for that specific antibody or disease.

Vaccinations are given to do one of two things:

1. Give the animal antibodies that were produced by another animal (passive immunity)

2. Challenge the horse with just enough antigen that it will build its own antibodies (active immunity)

In both cases, the object is to protect the vaccinated animal against a specific disease. Vaccines contain either inactivated killed organisms or modified live organisms. The ideal vaccine:

* Prevents clinical signs of the disease

* Stimulates the immune response

* Produces durable immunity with a single dose

* Is safe with no side effects

* Is incapable of producing the disease

* Is stable during movement and storage

* Is economical

The efficacy of any vaccine can be influenced by the type of vaccine, site of action, normal antigenic variation, and age of the horse when vaccinated. Various stresses also reduce an animal's ability to respond to a vaccination.

Table 14-3 gives examples of vaccination programs and schedules for some common equine diseases.


Disease is any condition of a horse that impairs normal physiological functions. Disease increases costs, reduces performance, and can limit growth in the young horse.

Two broad categories of disease affect horses: infectious and noninfectious diseases. Infectious diseases are caused by pathogenic organisms present in the environment or carried by other animals. In contrast, noninfectious diseases are caused by environmental problems, nutritional deficiencies, or genetic defects. Noninfectious diseases are not contagious and usually cannot be cured by medications. Noninfectious diseases are often a management problem.

Infectious Diseases

Infectious diseases are broadly categorized as parasitic, bacterial, and viral. Both internal and external parasites can affect horses (Figure 14-6). Parasitic diseases are discussed in Chapter 15.

Bacterial diseases are often internal infections and require treatment with antibiotics. Bacterial diseases can also be external, resulting in erosion of the skin and ulceration.

Viral diseases are impossible to distinguish from bacterial diseases without special laboratory tests. They are difficult to diagnose, and no specific medications are available to cure viral infections. Immunization can protect horses from some viral diseases, but vaccines do not exist for all the viruses that cause disease in horses.


Noninfectious Diseases

Noninfectious diseases can be broadly categorized as environmental, nutritional, or genetic. Many nutritional diseases are caused by the lack of or excess of a nutrient. Many of these are described in Chapter 12. Environmental diseases include natural or man-made toxins in the environment. Genetic diseases are covered in Table 10-4 in Chapter 10.


For the purpose of discussion, following are some of the more common and/or serious diseases of horses. They are categorized as respiratory diseases, digestive diseases, and other common diseases of horses.

Respiratory Diseases

The principal use for most horses depends on their athletic ability, which requires physical soundness. Any disease that affects the respiratory system may potentially interfere with the horse's soundness of wind and thus its overall athletic ability.

Some disease conditions may interfere with respiratory health. Respiratory disease can affect horses of any age, and chronic problems may seriously reduce the usefulness of horses at maturity.

Respiratory diseases can be caused by bacterial or viral agents, anatomical problems, allergic responses, or a combination of these.

Sinusitis. In this condition, the sinuses of the horse's head become inflamed. Causes include infectious agents, structural problems, and tumors.

Sinusitis is rarely contagious unless it is caused by a specific virus or bacterium. The person who cares for the horse may notice a discharge from one or both nostrils. This may be quite thick and tinged with blood, and frequently has a strong, unpleasant odor. Occasionally, the side of the horse's face may appear swollen.

Veterinarians diagnose sinusitis by physical examination, cultures of the discharges, X-ray examination, and sometimes by surgery accompanied by biopsy or the removal of a small piece of the involved tissue.

Prevention includes periodic examinations for abnormalities, an active immunization program to prevent infectious diseases, and periodic dental exams to prevent tooth disease from affecting the sinuses.

Palate Elongation. In this structural abnormality, the soft portion of the roof of the mouth extends too far back into the upper throat or pharynx, where it may interfere with breathing during strenuous exercise. Veterinarians diagnose the condition by examining the horse's throat with an endoscope, a flexible instrument with lights, that allows them to look into body cavities or spaces.

Horses cannot breathe through their mouths due to the physical design of the pharynx. Elongation of the soft palate reduces normal airflow to the point that a horse becomes unable to tolerate hard exercise.

This is a developmental problem of the horse's anatomy. Treatment consists of surgically removing the excess portion of the palate.

Bleeders. EIPH, or exercise-induced pulmonary hemorrhage (bleeding), is a serious condition in equine athletes. Racehorses are most frequently affected. The more strenuous the exercise, the more frequently bleeding occurs.

The hemorrhage occurs in minute vessels in the lungs. Although seldom fatal, bleeding can interfere with the horse's breathing and result in what appears to be choking or difficulty obtaining air.

Since blood does not always appear at the nostrils, owners may not be aware that bleeding is occurring. In some horses, blood flows from the nostrils when they lower their heads.

Heaves. Allergic equine respiratory disease is primarily seen clinically as a condition called heaves by horse owners, or pulmonary emphysema by veterinarians. It resembles asthma or emphysema in humans. Horses suffering from heaves exhibit reduced tolerance to exercise, a frequent soft cough, a distinct push with the abdominal muscles when air is being expelled, and a crackling or squeaking sound over the lung fields that can be heard with a stethoscope.

The condition frequently follows a bout of respiratory disease accompanied by severe coughing. It sometimes appears suddenly with severe respiratory distress in bronchial asthma-like attacks. The condition usually is progressive. Frequently it is associated with feeding of roughage containing a large amount of dust, pollen, or mold spores.

Aside from avoiding feeds that cause the condition, preventive steps include a vigorous vaccination program against infectious respiratory disease. Prompt treatment and adequate rest are required until the horse recovers. Treatment is a combination of several procedures. Nonallergenic, dust-free feeds and as much green pasture turnout as possible is needed. This may be combined with antihistamines, bronchial dilators, and/or regularly decreasing doses of corticosteroids. Sometimes atropine or atropine-like drugs help in acute cases. Some degree of follow-up nursing care will be needed for the rest of the horse's life.

Rhinopneumonitis. Equine herpesvirus types 1 and 4 (EHV-1 and EHV-4) cause rhinopneumonitis. In susceptible horses, especially foals, it is an acute upper respiratory infection with severe nasal discharge. Direct contact spreads the virus between horses.

After exposure, susceptible horses may develop a temperature of 102[degrees]F to 107[degrees]F for up to a week. Other signs include depression, loss of appetite, a watery nasal discharge, and a mild cough. Immunized horses usually develop a milder infection or even an infection without any signs. Occasionally, the virus enters the central nervous system and causes mild to severe incoordination that can progress to total paralysis.

Pregnant mares without immunity to EHV may abort. Abortions usually occur from the 8th through the 11th month of pregnancy. Occasionally, weak foals are born but die shortly after birth. Mares abort without warning and breed back without difficulty. Although some specific signs may occur in aborted foals, laboratory diagnosis is best.

Prevention by immunity from either natural exposure or vaccination is relatively short-lived. Repeated exposure or repeated immunizations enhance protection.

Vaccination programs vary, but generally include vaccinating with either a modified live virus vaccine at 2- to 3-month intervals year-round or using the killed product at the 5th, 7th, and 9th month of pregnancy. No effective treatment is now known. Vaccinating foals at 90 days of age and repeating at 120 days of age reduces the clinical signs in foals.

Horse farms must isolate pregnant mares and foals from contact with temporary stock. Show and racehorses returning to the farm or mares visiting for breeding are sources of infection. No other animals or humans are known to be affected by this virus.

Influenza. Influenza is an acute, highly contagious disease that causes a high fever and persistent cough. Flu is caused by at least two distinct myxoviruses that are widely spread throughout the horse population. Exposure occurs at shows, sales, races, trail rides, and other events where horses come together from different areas.

Following exposure to nasal discharges containing influenza virus, the susceptible horse develops a temperature of up to 107[degrees]F within 3 to 5 days. The fever may persist for up to 3 days. A hard, persistent cough develops early and persists for up to 2 to 3 weeks.

Secondary bacterial infections sometimes develop as a complication. Muscle soreness and stiffness are occasionally seen.

Good nursing care is the best treatment. This includes providing a soft, palatable, dust-free diet and fresh, clean water, while preventing drafts. Bandaging of legs and blanketing may help.

Horses should not return to work of any kind for 10 to 14 days after complete cessation of all flu symptoms. If the horse returns to work too soon, recurring bouts or other complications usually result.

Use of antibiotics or fever-controlling drugs are seldom needed and should only be given following a veterinarian's advice. Serious complications occur when a horse's symptoms are masked by medication, since the horse returns to work too soon.

A vaccine containing two inactivated viruses provides some prevention. An initial vaccination followed by a booster in 4 to 6 weeks is recommended. Follow-up boosters are given at 3- to 6-month intervals. The more likely the horses are to be exposed, the more frequent the boosters are recommended (Figure 14-7).

Pinkeye. Viral arteritis, or pinkeye, is a separate viral disease that can cause respiratory symptoms along with swelling of the legs and abortion in pregnant mares. This usually is a sporadic disease spread by contact with infective nasal discharges.

Few horses die unless complications occur. Young or very old horses are most severely affected. Up to 80 percent of infected pregnant mares may abort. Severity apparently varies greatly between outbreaks.

Symptoms occur 1 to 8 days following exposure. Swelling and redness appear around the eyes, with flowing of tears and squinting. Horses are dull and go off their feed. Eyelids, legs, and the underside of the body become swollen. Some yellowing or jaundice may be noticed. Pregnant mares abort during or shortly after the fever occurs.

Complications can include fatal lung disease due to accumulation of fluid. This is especially dangerous if the horse has already had a lung disease.

Veterinarians diagnose viral arteritis by clinical signs and differentiating it from several other viral diseases.

Treatment in general consists of very careful nursing care. The specific treatment depends on the individual case. Vaccines are currently available. Prevention is best accomplished through good sanitation and isolation.

Strangles. This is a highly contagious abscess-producing infection caused by a specific streptococcus bacterium, Streptococcus equi. Pus from ruptured abscesses can contaminate the environment, including mangers, fences, and water tanks. This material remains infectious to other horses for months and is a major means of prolonging an outbreak of the disease on a farm.

Young horses are most frequently affected, but susceptible horses of any age may develop the disease following exposure. Stress created by hauling, weaning, weather changes, hard work, and poor nutrition all weaken a horse's defense. Outbreaks tend to be prolonged and may follow introduction of an apparently healthy carrier.


Only horses, mules, ponies, and related equidae (zebras and others) are susceptible. Other domestic animals and humans do not develop the disease.

Three to 6 days following exposure, infected horses stop eating. They may extend their heads and drool. Swallowing is painful. A temperature of 106[degrees]F is not unusual.

Swelling between the jaws and near the base of the ear may occur. These swellings enlarge, become soft, burst, and drain a creamy, blood-tinged pus within 5 to 7 days.

Once the abscesses drain, the temperature frequently returns to normal or near normal. During the period when the temperature is high, the horse appears very depressed and may lose a considerable amount of weight.

The entire course of the disease in an uncomplicated case takes 4 to 6 weeks. Complicated cases may be prolonged for months, with failure of lesions to heal, severe weight loss, and extensive abscess formation throughout the animal's body.

If new horses are added regularly to a herd, the disease can reoccur. The infection rate is high, with over 80 percent of exposed horses showing signs of the disease. Death losses usually are low if no complications occur.

Death may occur either from abscesses rupturing within internal organs or from choking due to large abscesses blocking the horse's ability to breathe or breaking into the horse's airway, resulting in suffocation.

After the apparent recovery of an affected horse, considerable rehabilitation time is necessary to avoid a flare-up of infections in the throat (guttural pouches) and development of internal abscesses; swelling of the legs, head, or abdomen; and joint infections, especially with foals and yearlings.

Veterinarians diagnose strangles by its clinical appearance plus culture and identification of the organism Streptococcus equi. Other streptococci can cause a similar but milder disease that resembles strangles.

Commercially available vaccines prevent strangles. Two or three injections at 1-month intervals are given deep in heavy muscles. Boosters are given annually. Vaccination of horses during an outbreak or while recovering from the disease can be disastrous. Only healthy, uninfected, unexposed horses should be vaccinated. More recently, intranasal (modified live bacteria) vaccines are also provided for use for the prevention of strangles.

Treatment is best determined by a veterinarian. Applying hot packs on forming abscesses, cleaning abscesses, and providing easily eaten feed and fresh, clean water are essential. Isolating infected animals in one spot and leaving them there until completely healed prevents widespread contamination from the contents of abscesses.

Streptococcus equi is highly sensitive to penicillin, but vigorous and prolonged treatment is necessary. Recommended doses of penicillin should be administered daily and for several days after the horse's temperature returns to normal. This usually requires treatment for a minimum of 10 to 14 days.

Discontinuing treatment too soon, reducing dosage, skipping days of treatment, or using inappropriate drugs or dosages are the most frequent causes of treatment failure.

Pleuropneumonia. This disease condition usually is the aftereffect of an earlier respiratory problem and can be caused by several different organisms. Inflammation develops in the tissues that line the chest cavity and surround the lungs. This space fills with fluid, debris, and infective bacteria.

Pleuropneumonia results from incomplete or improper treatment of a previous lung disease. In most cases, corticosteroids or other anti-inflammatory drugs were used. Occasionally, inadequate dosages of antibiotics or sulfa drugs were given, or treatment was not carried out for long enough.

Pleuropneumonia is usually considered a contagious disease. The condition is painful, and the horse is reluctant to move. Pressure over the chest area causes discomfort, and some horses act as though they have colic or abdominal pain.

The veterinarian diagnoses the disease by listening to the horse's chest with a stethoscope for abnormal lung sounds, by observing the horse's painful attitude, by noting sounds of increased density on percussion, and finally, by performing a chest tap--drawing fluid for examination.

Avoiding respiratory disease in horses is the best prevention. This includes providing a clean, healthy environment, ensuring a complete immunization and internal parasite control program, and avoiding undue stress. If respiratory disease occurs, prompt, appropriate treatment is necessary for the indicated length of time.

Treatment may consist of drainage by tubes surgically implanted in the chest, specific antibiotic treatment, and good nursing care.

Abscess Pneumonia. This is a serious disease of foals. The bacterium Rhodococcus equi causes heavily encapsulated abscesses to develop in the lung, where they displace lung tissue. In severe cases, extensive destruction of lung tissue occurs. The bacterium seems to be very irritating to tissue and causes severe tissue reaction.

Symptoms seldom are evident until the disease has progressed to a critical stage. In the early stages, only a dry, persistent cough is present. Veterinarians diagnose the disease in foals by the symptoms, cultures of the trachea (windpipe), and age of the foal (usually 4 to 8 weeks when the disease is first noticed).

As the disease progresses, the foal develops severe breathing difficulty. Any exercise worsens the condition. Rectal temperatures generally are in the 102[degrees]F to 104[degrees]F range.

Death is usually due to asphyxiation as lung tissue is destroyed. Foals that recover may show no aftereffects as adults, despite the severity of symptoms during the disease's course.

Abscess pneumonia appears to be increasing in frequency, and several colleges of veterinary medicine are studying the disease. No effective commercial vaccine is currently available for use in horses. Prevention is best accomplished by superior management, especially internal parasite control, dust control, avoiding overcrowding, increased use of pasture, and minimizing enclosed housing.

Treatment with antibiotics should be vigorous and prolonged. Foals that respond must be treated for extensive periods of time--twice daily for up to 6 weeks is a fairly common treatment schedule.

Hot, dry, dusty conditions tend to result in an increase in this condition. The disease is not felt to be highly contagious, since large numbers of foals in a group usually are not affected.

When respiratory disease complications occur, problems can become more serious or even fatal. These complications have various causes. For example, some drugs cause horses to appear better, but they suppress the horses' own defenses. The infection spreads and the condition worsens. Then secondary bacterial infections follow. Cultures and identification are necessary to treat these conditions specifically.

Adequate time for complete recuperation is absolutely essential. Green grass, fresh air, and being outside are all beneficial to recovery.

Digestive Diseases

Digestive diseases are a frequent problem of horses; insurance companies cite colic as the most frequent cause of death in horses insured against loss. The following is a discussion of some of the more frequently seen causes of digestive disturbance.

Problems in the mouth--the beginning of the digestive tract--can result in improper chewing of food, which can then hamper swallowing and digestion. Malformed mouth parts on newborn foals should always be evaluated. Some abnormalities may be repaired surgically, while others may be impossible to correct. Because many of these conditions are considered heritable, use of these animals as breeding stock should be discouraged.

Wry muzzle, cleft palate, and overshot or undershot jaws are all conditions affecting horses. Their importance depends on their severity. These problems not only affect eating, but can seriously interfere with the use of bits for control when the horse becomes old enough to train for riding or driving.

Since dental disease may occur at any age, horses should have their mouths examined twice yearly for dental abnormalities. Although caries, or cavities, are uncommon, abnormal or uneven wear is frequently observed and needs correction.

Young horses lose their baby teeth from 2 to 5 years of age. At times, these teeth are not shed normally, and it becomes necessary to assist in their removal. When sharp points develop along edges of the grinding or jaw teeth, they irritate the inside of the lips and edges of the tongue. These sharp points are filed down with specially designed files called floats.

Horse owners can recognize possible dental problems when horses begin chewing abnormally, twist their heads sideways, drop excessive feed from their mouths, or refuse to eat hard grains or pellets.

Foreign bodies in the mouth cause similar problems. Grass awns, pieces of wood or metal, corncobs, and other items may lodge in the mouth and interfere with eating.

Proper feeding practices, such as using only clean feed boxes and avoiding hay with foxtail or similar type awns (bristles) in it, can prevent foreign bodies in the mouth.

Choke. Choke is a condition in horses that occurs when feed becomes lodged in the esophagus. While choke seldom is life threatening, it is uncomfortable to the horse. Many horses become excited and lunge about, trying to dislodge the material causing the choke. In the process, they may injure their handler or themselves.

Choke usually occurs when horses attempt to eat too fast or are fed very finely ground or very dry feed. Grass clippings from lawns also can cause choke.

A horse with choke should be placed in a stall and allowed free movement of its head. Veterinarians usually attempt to remove a choke with a nasogastric tube and lavage, or flushing with water. Sedation may be necessary. Owners should not attempt to dislodge a choke themselves as injury to the esophagus or lungs may occur.

Horses that choke are prone to do it repeatedly. Such horses should be denied access to the type of feed or circumstances that may cause choking.

Use of large, flat-bottomed feed troughs or placing large rocks (softball size) in the grain box will slow down gluttonous eaters. Extremely dry or finely ground grain should not be fed. Adequate eating space also helps.

Colic. Colic is a broad term that describes a horse showing abdominal pain. This can be caused by a number of conditions.

When colic occurs, it is important to determine the exact cause if possible. Successful treatment often depends on a correct diagnosis. Any colic, no matter how mild, is an emergency. The potential for the condition to worsen is too great to risk delay in treatment.

A distended stomach, acute inflammation of the small intestine, parasites that cause decreased blood flow to the intestine, dry food impaction, or gas distention of the large bowel are all types of colic. The degree of severity as well as treatment required varies.

Owners first notice that a horse has colic when it stops eating and drinking. The horse may curl its upper lip, paw at the ground, and turn its head toward either side. More severe pain causes colicky horses to sweat, get up and down, and try to roll. The horse with colic indicates it is in severe discomfort.

Rapid breathing, profuse sweating, violent activity, and a cold, clammy feeling may indicate the horse has gone into shock and is in need of immediate professional attention.

Veterinarians attempt to diagnose the specific type and cause of colic. They use medication to control pain and the horse's response to help evaluate the severity of the condition. Reducing the pressure in the stomach is important; oral medication may be needed to lubricate a mass or prevent further gas distention.

Administering oral medication is dangerous and should be done only with great care. Any foreign material, including medicine, that accidentally enters the lungs can cause pneumonia.

In some cases, surgery is the treatment of choice. This means moving an extremely uncomfortable, sick horse to a veterinary hospital that has surgical facilities. The decision needs to be made as soon as possible, and necessary supportive treatment must be provided until the horse arrives at the hospital.

The most frequent causes of colic are internal parasites and sudden drastic changes in the feeding schedule, either in the amount or kind of feed. Autopsies of many horses that die from colic reveal related lesions due to internal parasites. Diarrhea, especially in young horses, can result in colic due to telescoping of the bowel. Any severe digestive upset has the potential to result in colic symptoms.

Prevention of colic includes:

* An ongoing parasite control program, especially for young animals

* Maintaining a regular feeding schedule using only quality feeds

* Avoiding sudden dietary changes in kinds or amounts of feeds

* Providing salt and clean, fresh water free-choice at all times

Treatment of this emergency condition is best left to professional veterinary care.

Potomac Horse Fever. Acute infectious diarrhea syndrome, or Potomac horse fever, is a severe diarrhea condition of horses. Most affected animals are adults that may recently have been under stress. About 30 percent of horses with Potomac horse fever die.

Potomac horse fever seems to be caused by the bacterium Ehrlichia risticii. It can occur sporadically, with only one horse on a farm being affected. An arthropod carrier is suspected, but no particular species has been identified.

Most cases have occurred in Maryland, Virginia, and southeastern Pennsylvania, but similar cases have been reported in other areas of the country.

Infected horses become depressed, stop eating, and develop a profuse, watery diarrhea. Some horses will have a fever of up to 105[degrees]F before the diarrhea starts. With continued diarrhea, the affected horse becomes weaker and develops signs of shock. The disease does not seem to be contagious and does not affect humans.

Treatment to replace fluids and control the diarrhea must begin as soon as possible. Large volumes of intravenous fluids and antidiarrheals are necessary. Time required for almost constant treatment becomes extensive and fairly expensive. Antibiotics are effective against Ehrlichia risticii.

Other Diarrheas. Other causes of acute diarrheal disease in horses include colitis, salmonellosis, and other diarrheal syndromes. Most of these are related to or follow stress, such as hauling, respiratory disease, or surgery. In some cases, such as salmonellosis, the diarrhea is contagious between horses and may infect humans.

Most of these diarrheas respond to vigorous treatment, although laminitis or founder frequently occur following a severe diarrheal episode. Sometimes a horse will recover and be left with chronically soft stools.

Specific treatments or preventions are not available at this time. A vaccine is available for salmonellosis.

Foal Heat Diarrhea. Most newborn foals develop diarrhea at 7 to 12 days of age. At about the same time, the mare comes into what is called foal heat.

Affected foals usually show no problems due to the diarrhea, but occasionally they become ill or the diarrhea persists. Some may even develop serious intestinal problems and colic.

The cause is felt to be related to larvae of the intestinal threadworm, Strongyloides westeri. The immature larvae locate in the mare's udder, and the foal becomes infected by nursing. Within 8 to 10 days, the parasites are established within the foal's intestinal tract, where they irritate the gut wall, causing diarrhea.

Deworming pregnant mares during the last 30 days of pregnancy prevents the S. westeri larvae.

Affected foals may respond to intestinal protectants, appropriate deworming agents, and fluids, if needed. Oral antibiotics seldom are of much value.

A secondary problem is the scalding of the foal's rear quarters, with resultant burning, irritation, and hair loss. To prevent this, horse owners must clean the foal's rear parts and place some protective ointment on the area. Applying Vaseline or zinc oxide ointment to the foal's tail helps, as it becomes a natural applicator.

Seemingly harmless diarrheal conditions can rapidly become critical. Horse owners need to keep a close watch on any animal with diarrhea. Proper treatment and aftercare are essential to minimize resultant problems.

Laminitis. Laminitis is defined as an inflammation of the lamina of the inner hoof wall. Laminitis and a process called founder are often thought to be the same problem. Laminitis is due to metabolic changes that affect the lamina. Founder is the mechanical displacement of the coffin bone within the foot. Founder is associated with laminitis, but it is possible for a horse to have laminitis without founder.

Laminitis is difficult to prevent because there are many different causes, some of which may act together to cause this lameness. One cause of laminitis is colic, especially with grain overload. Eating too much grain results in a high production of lactic acid in the horse's intestinal tract. The lactic acid damages the gut wall and allows bacteria to enter the blood. This results in endotoxemia (the presence of toxins in the blood), which affects the lamina by decreasing the blood flow to the lamina. Colic can also cause laminitis by direct damage to the intestinal wall, such as with a torsion (twist of the intestine). The wall will die in that area and, again, allow bacteria to get into the blood.

Another cause is a dystocia or retained placenta in the mare. Stress, exhaustion, or infections that stress the horse for extended periods can also cause laminitis.

Leg problems are another major cause of laminitis. With excessive, repetitive stress and concussion put on the leg, the blood flow to the lamina can be decreased. This damages the lamina. Lameness causes a horse to shift its weight onto the good leg. This excess stress can also lead to laminitis.

The first signs of laminitis are often subtle and can be easily missed. However, the condition develops rapidly; if it is not caught immediately, the horse can quickly become quite lame. Initial signs include restlessness or agitation--the horse will pace around the stall and shift its weight back and forth between its feet. Within the first day, the horse is often reluctant to turn, and its gait will be stiff. In the first 2 days, the horse often assumes the classic laminitis stance, to shift weight onto its heels and off its toes, which hurt. Digital pulses will often be moderate to bounding by this time, and there is usually a depression at the apex of the coronary band. By this stage, it is essential to get the horse under a veterinarian's care.

The next signs that develop include a bulging of the sole downward toward the ground so that it is not concave anymore. The coffin bone in the foot rotates (founder), which may be visible on a radiograph taken by the veterinarian. Within 4 to 5 days, a separation of the hoof wall from the skin at the level of the coronary band is possible. The coffin bone may have rotated enough by this time to have perforated the sole. This is a serious situation (Figure 14-8).

As soon as signs of laminitis are noted in a horse, a veterinarian should be called. The horse is usually treated with drugs to decrease the inflammation. Special pads are put on the sole to support it. Early in the course of laminitis, special shoes can be put on the feet to elevate the heel and take pressure off the deep flexor tendon that is responsible for the rotation of the coffin bone.

Hot- and cold-water soaks are often used to increase circulation to the lamina and cool the feet. This also helps make the horse more comfortable. The stall should be deeply bedded to help cushion the feet. If a medical reason for the laminitis exists--for example, colic--treatment of that problem needs to be initiated.

A horse that has suffered only a mild case of laminitis may recover without complication and may be able to return to its normal level of exercise. The veterinarian will have to work with the owner or trainer to determine the amount of damage and monitor the horse's recovery.

Chronic laminitis can be detected by changes in the hoof wall. Regular disturbances of the blood flow to the lamina will result in changed growth rate of the hoof wall. The heel will grow faster than the toe, and the growth rings will be farther apart at the heel. These changes should be looked for when purchasing a horse.


Blister Beetles

Blister beetles, of the insect family Meloidae, defend themselves with a toxic secretion, cantharidin, that causes severe irritation to the skin and mucous membranes of warm-blooded animals. If whole or crushed parts of blister beetles are ingested by a grazing animal, the cantharidin can cause irritation and hemorrhages in the stomach. The amount of cantharidin produced varies from male to female and among species of blister beetles (Figure 14-9).

Among domestic grazing animals, horses are most susceptible to this toxin. Only a few beetles, eaten with hay, can cause severe illness or even death to a horse. Affected horses exhibit signs of colic, frequently void small amounts of blood-tinged urine, and at times have muscle tremors. If blister beetle poisoning is suspected, a local veterinarian should be consulted immediately so treatment can be started.

Blister beetles commonly feed on alfalfa and the flowers of various plants that frequently grow in hay fields. The problem occurs when the hay-harvesting process crushes or grinds up blister beetles, and their toxic parts remain in hay that is fed to horses.

Some steps can be taken to reduce the possibility of incorporating blister beetles in hay. First-cutting hay seldom contains blister beetles if it is cut in early to mid-June, before the adult beetles are present in alfalfa. Blister beetle poisonings have increased since the advent of swather-conditioning equipment that runs hay between rollers or crimpers. Hay-conditioning equipment will kill many beetles as they pass through the rollers, contaminating several feet of windrow with crushed beetle parts. However, separate cutting followed by windrowing allows the beetles to find their way out of windrows while the hay is drying and prior to baling.


Other Common Diseases

Clostridial diseases as a group are caused by a family of bacteria that grow in the gut or tissue and produce gas and very powerful toxins that affect the nervous system.

Tetanus. Tetanus, a common disease of horses sometimes called lockjaw, is caused by a neurotoxin produced by Clostridium tetani. This nerve-tissue poison causes spasms and rigidity of the skeletal muscles. Affected horses cannot eat and have difficulty drinking. Over half of affected horses die due to suffocation, starvation, or dehydration.

Due to the large number of tetanus bacteria in the horse's digestive tract, people working around horses should consult their physicians concerning tetanus immunization for themselves.

Infected horses acquire the problem through puncture wounds or other deep wounds. Within 10 to 14 days following injury, horses become increasingly nervous, and then stiff or rigid, and they have difficulty moving. The more rapid and severe the onset of symptoms, the less chance of recovery.

Persistent treatment and much nursing care are needed. Affected horses need to be protected from light and sound that can stimulate nervousness. Horses are placed in darkened stalls and their ears plugged with cotton to reduce stimuli from sound.

Veterinarians usually administer tetanus antitoxin, antibiotics, and sedatives repeatedly for several weeks. One-third to one-half of affected horses may recover if diagnosed early and treated vigorously. Prevention is twofold. Unvaccinated animals should receive tetanus antitoxin within 24 hours following injury or surgery. This provides temporary protection for 10 to 14 days. If healing is not complete at that time, tetanus antitoxin should be repeated at 2-week intervals until healing is complete.

Vaccination with tetanus toxoid provides a very stable immunity. All horses should be vaccinated against tetanus and receive boosters once a year and following an injury.

Botulism. Botulism is caused by Clostridium botulinum and can occur in adults as forage poisoning or in foals as shaker foal syndrome.

With forage poisoning, adult horses become weak and stagger, have difficulty swallowing, and may go down and be partially or completely paralyzed. Silage, incompletely cured hay, and forage with spoiled areas are usually the causes. Prevention is best accomplished by careful selection of hay, silage, or other harvested forage for horses.

Shaker foal syndrome appears as a problem in young foals nursing mares that are being fed high-energy, high-protein diets. Experimental vaccination of pregnant mares prior to foaling has prevented the condition, and a vaccine may become available commercially.

Care in nutritional management of mares nursing foals may control or prevent the condition from developing in foals. Affected foals become uncoordinated, develop jerky movements, and eventually become paralyzed and die. Once symptoms are apparent, treatment has little effect.

Clostridial Myositis. Infections of muscle masses by one or more of several clostridial bacteria families can occur. These organisms usually enter through wounds, needle injections, or other muscle injury.

The bacteria grow rapidly, form gas pockets, create severe pain, and cause shock from the toxins produced. Hand pressure causes both crackling sounds and sensation due to the gas formed under the skin. Often, cattle are or have been present when a problem occurs.

Veterinarians treat this condition by promptly establishing drainage and using adequate dosages of appropriate antibiotics. Despite vigorous treatment, some cases fail to respond.

Appropriate injection techniques, avoiding the use of irritating drugs, and not injecting excessive volumes at one site are all important in preventing clostridial myositis. Prevention of injuries and prompt attention to any wound are helpful in preventing this disease. No approved vaccines are available.

Sleeping Sickness. This disease is also called equine encephalomyelitis. Three forms of this disease are caused by viruses that affect the nervous system. Wild animals and birds act as reservoirs. Mosquitoes are the principal means of virus transmission between victims. Horses at pasture are more susceptible than stabled horses. The viruses also can affect humans. In the Eastern and Western forms of the disease, horses are last hosts and the virus does not spread from them. Venezuelan encephalomyelitis, however, spreads between horses and from horses to humans.

Infected horses initially develop a fever, act as though they have problems seeing, wander aimlessly, stagger, grind their teeth, and have a drooping lip. The disease may progress until paralysis occurs. Horses with mild cases recover slowly over several weeks.

From 25 percent to 50 percent of horses infected with the Western form may die, over 90 percent infected with the Eastern form die, and 75 percent infected with the Venezuelan virus die.

No specific treatment is available, but veterinarians can provide supportive care. Mosquito control is an important preventive measure, as is annual vaccination. The Venezuelan form has not been a problem in the United States since 1971, but it could enter this country from Latin America.

Highly effective vaccines are commercially available and should be administered annually, before the mosquito season. They may be combined with other vaccines.

Swamp Fever. Equine infectious anemia (EIA), or swamp fever, is a viral disease. In the acute form, it causes severe red blood cell destruction resulting in anemia. Recovered animals are carriers. The virus is spread by bloodsucking insects and by repeated use of needles or instruments without adequate sterilization between patients.

The disease causes severe anemia, fever, weakness, weight loss, edema, and sometimes death. Inapparent infections show few, if any, symptoms. Horses, without visible signs of infections, that receive regular hard physical work or some other stress frequently begin to show clinical signs of the disease.

Clinical diagnosis of EIA is by a positive antibody level test. Titers (levels) causing a positive test occur 2 to 4 weeks after exposure to the initial disease.

No effective treatment is available. Prevention is best accomplished by maintaining horses that test negative for the antibody. Fly control and use of disposable needles among horses are also important aspects of control. Any horse with a positive antibody test should be maintained away from uninfected horses, especially during the insect season.

West Nile Virus West Nile is a type of virus that causes encephalitis, the inflammation of the brain. The virus is most commonly spread by mosquitos that have acquired the disease from infected birds. Because mosquitoes transmit the disease, it has the potential to affect humans, livestock, and poultry. The first documented case of the West Nile Virus in the United States was reported in September of 1999.

Symptoms of West Nile Virus typically develop between 3 to 14 days after being bitten by an affected mosquito. Symptoms include ataxia, or stumbling and incoordination; depression or apprehension; weakness of limbs; partial paralysis; the inability to stand; and sometimes death. Horses may be infected without showing any clinical signs.

Protecting your animals from mosquito bites is the best method of preventing the spread of the virus. Eliminating any potential mosquito breeding site is essential. Mosquitoes tend to breed in sources of still water. These can include discarded tires, bird baths, clogged roof gutters, outdoor water-holding devices, any puddle that lasts for more than 4 days, and water that may have collected on top of a swimming pool cover.

A vaccine for horses has been approved, but its effectiveness is unknown. Call a veterinarian if the disease is suspected.

Rabies. Rabies (hydrophobia) is a universally fatal viral disease of the central nervous system. The virus is transmitted in saliva and infects humans, as well as other mammals. Wild animals, especially raccoons and skunks, appear to be important reservoirs of the disease.

When horses come in contact with rabid wild animals, their curiosity often results in their being bitten on the muzzle. Symptoms of rabies usually occur within 2 weeks following the bite.

A sudden change in behavior is the first indication of rabies. Drooling may or may not occur. After 1 to 3 days, horses may suddenly become vicious, attempting to bite without a reason. Some roll extensively, as if they had colic. The size and strength of horses makes them dangerous and potentially unmanageable. Self-mutilization is common.

Treatment is not considered effective, feasible, or safe for the humans involved. An animal suspected of having rabies should be confined for 2 weeks. If the horse is then destroyed, care should be taken not to damage the brain. A veterinarian will remove the head and prepare it for submission to a laboratory for examination at once to confirm the diagnosis of rabies.

Horses may be protected against rabies by vaccination with an approved product properly administered by a licensed veterinarian.

Vesicular Stomatitis. Vesicular stomatitis occurs in the United States from time to time; some strains of the virus that causes it are foreign. Vesicular stomatitis gets its name from the appearance of blisters (vesicles) and raw ulcers in the mouth (stoma) of infected horses, swine, cattle, and humans. It is characterized by blisters on the tongue, teats, soles of the feet, and the coronary band.

Insects and the transporting of animals are probably responsible for the spread of the disease. The incubation period is about 2 to 8 days but may be longer.

No specific treatment is available. Animals should be protected from a secondary infection in the lesions. Prevention involves restricting the movement of animals during outbreaks, disinfecting trailers and stalls, and controlling insects. A vaccine is available.


Poisonous plants in the form of wildflowers or weeds may be found in both hays and pasture. Plants poisonous to horses can also include cultivated plants that were never intended for horse feed and trees near where horses are kept. Some of these common poisonous plants and their effect on horses are listed in Table 14-4.

Poisonous plants are not harmful until a horse eats them. The best way to protect your horse from eating poisonous plants is good management:

* Provide sufficient high-quality forage

* Manage pasture to prevent overgrazing and to control weeds

* Be knowledgeable and particular about the plants growing on your property

* Take time to inspect the hay you feed for weeds

Some plants are not poisonous but they can still injure a horse, causing the animal discomfort or pain. These include such plants as sand burrs, thistles, foxtail, cactus, goat head, stinging nettle, and cockle burrs. Most of these plants cause sores in the mouth that make horses slobber and have difficulty eating. Some plants may cause skin irritations or eye injury.


Equine first aid is the emergency care given to an injured or ill horse before treatment; it can be administered by a veterinarian or until the horse can be transported to a facility where help is available. The objectives include:

1. Intervening with a life-threatening situation

2. Recognizing serious or potentially serious, life-threatening conditions such as hemorrhage (bleeding), fracture, dehydration, and shock

3. Using measures to minimize further damage and prevent complications or aftereffects such as:

Extension of bone damage

Damage to blood vessels or nerves

Damage to soft tissue

Secondary laminitis

Preliminary information--temperature, heart rate, respiratory rate, color of mucous membranes, and capillary refill time--are vital statistics that will help a veterinarian evaluate an emergency situation over the phone. Also, a description of what caused the emergency can help with initial diagnosis and/or treatment. A well-equipped first aid kit will help the horse owner treat many minor ailments and cope with emergencies while waiting for the veterinarian to arrive.
First Aid Kit

* Water-soluble antibacterial ointment
and/or spray (e.g., Betadine)

* Bandage material:

1 roll nonsterile cotton
Sheet cottons or quilts for leg wraps
Brown gauze or polo wraps
Tefla pads
Kling rolls
4 x 4 in. sponges
Vetwrap[TM] or other self-adhesive

* Poultice

* Rubbing alcohol

* Soap

* Epsom salts

* Thermometer with string and clip

* Scissors

* Stethoscope

* Clean towels

* Hoof pick and knife

* Shoe pullers

* Fly repellant

* Flashlight

* Prescribed, nonexpired medications

* Large syringe

A Modern Equine Medical Center

Modern equine medical centers provide services once reserved for
humans. High-speed treadmills, aquatreds, recovery pools,
completely equipped equine ambulances, and in-house laboratories
are frequently available at these facilities.

High-speed treadmills are used for gait analysis, stress testing,
respiratory examination, and physical therapy. The treadmill speed
ranges from 1 to 33 miles an hour, and the treadmill can be
elevated to a slope of 6 degrees to increase the work level.

An aquatred is a water-filled treadmill sunk into the ground. It
assists in the conditioning and recovery of orthopedic, laminitis,
and soft-tissue injury cases. The aquatred offers an adequate level
of exercise while protecting the skeletal system and providing
soft-tissue hydrotherapy.

The 8-foot-deep recovery pool is heated and equipped with Jacuzzi
jets to provide a warm, relaxing, safe environment for a horse
recovering from anesthesia. The pool is frequently used for
postsurgical care of horses with fragile orthopedic problems.
Jacuzzi jets provide soft-tissue therapy and serve to relax the
recovering horse.

The recovery pool is also used for physical therapy. A high-powered
ski jet propels water from the front of the pool to provide a force
for the horse to swim against. It is ideal for use in soft-tissue
therapy in laminitis or recumbent (lying down) horses. The warm
water and Jacuzzi also relieve sore muscles and other problems
associated with chronic recumbence.

Completely equipped equine ambulances are another service provided
by modern clinics. The ambulance contains a winch and transport mat
capable of quickly and safely moving any size recumbent patient
from up to 100 feet away into the ambulance. A complete triage or
medical assessment facility, the ambulance and accompanying team
are prepared to aid fracture patients, combat shock, deal with
cardiovascular emergencies, provide respiratory support, and
anesthetize a patient safely for the entire trip to the medical
facility if necessary. Complete anesthetic monitoring is possible
in the ambulance, as are the ability to provide intravenous fluids,
emergency drugs, hemostasis, and triage fracture stabilization.

Modern equine medical centers may also be equipped with an in-house
hematology, chemistry, and microbiology laboratory that provides
many results within minutes of obtaining a sample. These results
can be essential to rapid treatment of emergency cases.

Based on the value of some horses, no cost is too great for full
recovery, which now can often be achieved due to the services of a
modern equine medical center.


Horse owners need to be able to recognize a healthy horse by observing the signs of good health. The immune system is essential to the health of the horse. Antigens induce antibodies that destroy harmful substances in the body. The immune system also remembers disease-causing invaders and is prepared for the next invasion. Vaccinations provide immunity to many problem diseases. Before the foal's immune system is developed, it receives its first immunity in the colostrum from the mare.

Many diseases can affect horses. These diseases can be grouped as infectious and noninfectious diseases. The infectious diseases can be caused by bacteria, viruses, or parasites. Noninfectious diseases are often due to a management problem. If owners are aware of the signs of these diseases, they can identify them in the early stages. Through good management and knowing which diseases are the most serious threat to horses, horse owners can minimize the spread of contagious diseases and effect prompt treatment of sick animals.


Success in any career requires knowledge. Test your knowledge of this chapter by answering these questions or solving these problems.

True or False

1. A horse's weight can change by as much as 50 pounds depending on recent eating, drinking, or elimination.

2. All energy provided above maintenance for the horse will go toward the formation of fat.

3. Immunity refers to the ability of an individual who has recovered from a disease to remain well after a second exposure to the same disease.

4. Antibodies are provided to the newborn foal during gestation.

5. EIPH is a serious problem in pregnant mares.

6. Horses can breathe through their mouths like humans.

7. Colic in a horse is always an emergency.

Short Answer

8. List 10 signs of good health in a horse.

9. What are the normal heart rate, respiratory rate, and temperature of the horse?

10. Name eight points of a good horse health program.

11. What term describes the process by which the mare passes antibodies to the foal?

12. List the two reasons vaccines are given.

13. Name the virus that is the cause of rhinopneumonitis in foals.

14. What disease is produced by the neurotoxin Clostridium tetani and affects humans as well as horses?

15. List four diseases of the horse caused by bacteria and four caused by viruses.

Critical Thinking/Discussion

16. List at least four pieces of information that will help a veterinarian evaluate an emergency situation over the phone.

17. Explain the two general responses of the immune system, and define the terms antigen and antibody.

18. Discuss the differences between infectious and noninfectious diseases, and give examples of each.

19. Describe the symptoms of and treatment for strangles.

20. Describe the general symptoms of colic, and list four steps to prevent its occurrence.

21. What is foal heat diarrhea?

22. Explain the difference between laminitis and founder and how they are related.

23. What is the best way to prevent a horse from eating poisonous plants?

24. Why is first aid important for horses and horse owners?


1. Based on the information in this chapter, develop a checklist of things to observe when examining horses for signs of disease. Make the checklist complete enough that it could be given to a new employee.

2. From a biological supply house or the biology department at a college or high school, obtain prepared microscope slides of bacteria. Observe the different shapes--rods, spheres, or spirals.

3. Research and report the role of bacteria in human health and commerce. Some bacteria cause disease, while other bacteria have a positive role in human welfare.

4. Using Table 14-4, identify poisonous plants in your area. Make a collection of these plants.

5. Visit with a veterinarian to discuss types of antibiotics and their effectiveness.

6. Put together a first aid kit for a horse, and develop a brief first aid manual to go in the kit.

7. Ask a veterinarian to describe a typical vaccination schedule for horses in your area. Make a table showing the annual cost to vaccinate a horse.

8. Using the Internet, research new vaccines being developed and find out what progress is being made on other horse diseases. Report your findings.

9. Working with a professional, take the vital signs of a healthy horse.

10. Construct a table that compares the vital signs of a horse to those of an adult pig, cow, and sheep.



Cheek, P. R. (2004). Applied animal nutrition: Feeds and feeding (3rd ed.). Upper Saddle River, NJ: Prentice Hall.

Evans, J. W. (2000). Horses: A guide to selection, care, and enjoyment (3rd ed.). New York: Owl Books.

Frandson, R. D., Fails, A. D., & Wilke, W. L. (2003). Anatomy and physiology of farm animals (6th ed.). Philadelphia: Lippincott Williams & Wilkins.

Griffin, J. M., & Gore, T. (1989). Horse owner's veterinary handbook (2nd ed.). New York: Howell Book House.

Hawcroft, T. (1997). First aid for horses: The essential quick-reference guide. New York: Howell Book House.

Kahn, C. M. (Ed.). (2005). The Merck veterinary manual (9th ed.). Whitehouse Station, NJ: Merck & Co.

Siegal, M. (Ed.), & School of Veterinary Medicine. (1996). Book of horses: A complete medical reference guide for horses and foals. New York: Harper Collins.

University of Missouri-Columbia Extension Division. (n.d.) Missouri horse care and guide book. Columbia: Cooperative Extension Service, University of Missouri and Lincoln University.

Worth, M. (2004). Storey's guide to feeding horses: Lifelong nutrition, feed storage, feeding tips, pasture management. North Adams, MA: Storey Publishing.


Internet sites represent a vast resource of information, but remember that the URLs (uniform resource locator) for World Wide Web sites can change without notice.

Using one of the search engines on the Internet such as Yahoo!, Google, or, find more information by searching for these words or phrases:

disease in horses

health management of horses

horse conditioning

horse nutrition




A search for any of the specific diseases will yield additional information. Table A-18 in the appendix also provides a listing of some useful Internet sites that can serve as a starting point for further exploration.
TABLE 14-1 Horse Condition Scoring System

Score   Condition Description

1       Poor. Animal extremely emaciated. Spinous processes, ribs,
        tailhead, and point of hip and point of buttocks project
        prominently; bone structure of withers, shoulders, and neck
        easily noticeable; no fatty tissue can be felt.

2       Very thin. Animal emaciated. Slight fat covering over the
        base of spinous processes; transverse processes of the
        lumbar vertebrae feel rounded; spinous processes, ribs,
        tailhead, and point of hip and point of buttocks prominent;
        withers, shoulders, and neck structures faintly discernible.

3       Thin. Fat built up about halfway on the spinous processes;
        transverse processes cannot be felt; slight fat cover over
        the ribs; spinous processes and ribs easily discernible;
        tailhead prominent, but individual vertebrae cannot be
        identified visually; point of buttocks appear rounded but
        easily discernible; point of hip not distinguishable;
        withers, shoulders, and neck accentuated.

4       Moderately thin. Slight ridge along back; faint outline of
        ribs discernible; tailhead prominence depends on conformation,
        but fat can be felt around it; point of hip not discernible;
        withers, shoulders, and neck not obviously thin.

5       Moderate. Back is flat (no crease or ridge); ribs not visually
        distinguishable but easily felt; fat around tailhead beginning
        to feel spongy; withers appear rounded over spinous processes;
        shoulders and neck blend smoothly into body.

6       Moderate to fleshy. May be slight crease down back; fat over
        ribs spongy; fat around tailhead soft; fat beginning to be
        deposited along the side of withers, behind shoulders, and
        along the sides of neck.

7       Fleshy. May have crease down back; individual ribs can be
        felt, but there is noticeable fat between ribs; fat around
        tailhead soft; fat deposited along withers, behind shoulders,
        and along neck.

8       Fat. Crease down back; difficult to feel ribs; fat around
        tailhead very soft; area along withers filled with fat;
        area behind shoulder filled with fat; noticeable thickening
        of neck; fat deposited along inner thighs.

9       Extremely fat. Obvious crease down back; patchy fat appearing
        over ribs; bulging fat around tailhead, along withers, behind
        shoulders, and along neck; fat along inner thighs may cause
        them to rub together; flank filled with fat.

TABLE 14-2 Signs of Health in the Horse

Sign                    Normal

Temperature             99.5[degrees]F to 101.5[degrees]F
Heart rate              32 to 48 beats per minute
Respiratory rate        8 to 16 breaths per minute
Mucous membranes        Pink color
Capillary refill time   1 to 2 seconds

TABLE 14-3 A Suggested Vaccination Program

Disease             Initial Vaccine Series   Booster

Tetanus             2 injections, 1 month    Annually or at time of
                    apart                    injury

Influenza           2 injections, 2 months   Annually or every 3 to 4
                    apart                    months for horses at risk

Rabies              2 injections at 3 and    Annually
                    12 months of age

Eastern, Western,   3 injections at 3, 4,    Annually, before onset of
Venezuelan          and 6 months of age      insect season

Rhinopneumonitis    2 injections at 3 and    Mares in 5th, 7th, and
(equine             6 months of age          9th months of pregnancy;
herpesvirus Type                             every 3 to 6 months for
I and IV)                                    horses in areas of risk

Botulism            3 injections, 1 month    Annually for broodmares;
                    apart                    1month prior to foaling

Equine viral        1 injection              Mares and stallions; 3
arteritis                                    weeks prior to breeding;
                                             inadvisable in late

Strangles           2 to 3 injections,       Annually or prior to
                    1 month apart            exposure

Potomac horse       2 injections, 1 month    Annual booster in May/
fever               apart                    June in high-risk areas

Anthrax             2 injections, 1 month    Annually to horses at
                    apart                    risk of exposure

Source: Art and Science of Equine Production, from University of

TABLE 14-4 Common Poisonous Plants

Common Name            Scientific Name        Location (1)

                              Wildflowers and Weeds

Blue flax              Linum spp.             Throughout
                                              North America

Bracken fern           Pteridium aquilinum    Forested areas

Castor-oil plant       Ricinus communis       Tropical areas

Death camas            Zigadenus spp.         North America

Fiddleneck             Amsinckia intermedia   Pacific Coast

Foxglove               Digitalis purpurea     Western United

Jimsonweed             Datura stramonium      North America

Larkspur               Delphinium spp.        West, Midwest
                                              United States

Locoweed               Astragalus spp.        West, Southwest
                                              North America

Milkweed               Asclepias spp.         North America

Monkshood              Aconitum spp.          West, Midwest
                                              United States

Nightshade             Solanum spp.           North America

Poison hemlock         Conium maculatum       North America

Pokeweed               Phytolacca americana   Eastern, Southern
                                              United States

Ragwort/               Senecio spp.           North America
hound's tongue

Sagebrush              Artemisia spp.         Western North

Saint John's wort/     Hypericum spp.         Western U.S.
Klamath weed                                  plains areas

Water hemlock          Cicuta spp.            North America

White snakeroot/       Eupatorium spp.        Eastern,

Jimmy-weed                                    Southern U.S.
                                              forested areas

Yellow star thistle/   Centauria spp.         Western United
Russian knapweed                              States, Canada

                                  Cultivated Plants

Alsike clover          Tribolium hybridum     Eastern, North
                                              central North

Avocado                Persea americana       Southern United

Azalea/laurel/         Rhododendron spp.      North America

Johnsongrass/          Sorghum spp.           North America
Sudan grass

Oleander               Nerium oleander        Southern United

Yellow oleander        Thevetia peruviana     Southern United

Yew                    Taxus                  United States


Black locust           Robinia pseudoacacia   Central,
                                              Southern United
                                              States, Canada

Black walnut           Juglans nigra          Northern,
                                              Central United

Chokecherry/wild       Prunus spp.            Southern,
black cherry                                  Northeast,
                                              United States

Elderberry             Sambucus spp.          Forested areas
                                              of United States

Horse                  Aesculus spp.          Southern,
chestnut/buckeye                              Eastern United

Red maple              Acer rubrum            Eastern United

Common Name            Toxicity (2)   Signs

                           Wildflowers and Weeds

Blue flax              +++            Rapid labored breathing,
                                      frothing at mouth

Bracken fern           +              Loss of flesh, lack of
                                      coordination, depression,

Castor-oil plant       +++            No appetite, constipation
                                      and diarrhea, hard breathing,

Death camas            ++             Stiff-leggedness,
                                      hypersensitivity, weakness,

Fiddleneck             ++             Photosensitization, weight
                                      loss, anemia, jaundice

Foxglove               +++            Heart irregularities; diarrhea;
                                      labored, rapid breathing

Jimsonweed             ++             Colic, diarrhea, dilation
                                      of pupils, excitability,

Larkspur               +++            Hypersensitivity, trembling,
                                      collapse, convulsions

Locoweed               +              Strange behavior, incoordination,
                                      odd head carriage,
                                      weight loss

Milkweed               +++            Lack of coordination, depres-
                                      sion, shallow breathing,
                                      unsteadiness, coma

Monkshood              +++            Hypersensitivity, trembling,
                                      collapse, convulsions

Nightshade             ++             Trembling, incoordination,

Poison hemlock         +++            Trembling, incoordination,
                                      salivation, colic, shallow
                                      breathing, coma

Pokeweed               ++             Diarrhea

Ragwort/               ++             Weakness, liver failure, yellow
groundsel/                            mucous membranes, incoordination
hound's tongue

Sagebrush              ++             Excitability, falling, front leg

Saint John's wort/     ++             Photosensitization
Klamath weed

Water hemlock          ++++           Rapid respiration and heart
                                      rate, violent spasms, coma

White snakeroot/       +++            Sweating, stumbling, spread-
Jimmy-weed                            legged stance, congestive
                                      heart failure

Yellow star thistle/   +              Inability to swallow food,
Russian knapweed                      tongue lolling, smile expression

                        Cultivated Plants

Alsike clover          +              Depression, colic, diarrhea,

Avocado                ++             Colic, diarrhea, noninfectious
                                      mastitis in lactating mares

Azalea/laurel/         ++             Diarrhea, colic, excessive
rhododendron                          salivation, depression,
                                      incoordination, stupor

Johnsongrass/          +              Frequent urination/defecation,
Sudan grass                           tremors, gasping, convulsions

Oleander               ++++           Sweating, bloody diarrhea,
                                      colic, difficult breathing,

Yellow oleander        ++++           Sweating, bloody diarrhea,
                                      colic, difficult breathing,
                                      arrhythmia, tetany

Yew                    ++++           Nervousness, difficult breathing,
                                      incoordination, convulsions


Black locust           ++             Diarrhea or constipation,
                                      stupor, laminitis, appetite

Black walnut           +++            Increased temperature, laminitis,
                                      swelling in legs, heart and
                                      respiratory rates increased

Chokecherry/wild       +++            Convulsions, frequent
black cherry                          urination/defecation,
                                      gasping, tremors

Elderberry             +++            Gasping, tremors, frequent

Horse                  ++             Incoordination, muscle
chestnut/buckeye                      tremors

Red maple              +++            Mucous membranes dark,
                                      depression, colic, urine red
                                      or brown

(1) Location refers to areas where the plant occurs naturally.
Many of these plants are cultivated outside the location indicated
on this table.

(2) The number of plus signs (+) indicates the relative toxicity of
the plant; four plus signs (++++) indicate the most toxic while one
plus sign (+) is the least toxic.

Adapted from "Poisonous Plants: A Survival Guide," by J. Moore,
Equus, 1995, pp. 28-37.
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Author:Parker, Rick
Publication:Equine Science, 3rd ed.
Date:Jan 1, 2008
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