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Chapter 24 Feeding horses.

A horse is dangerous at both ends and uncomfortable in the middle.


The nutritional phases in the horse production cycle, illustrated in Figure 24-1, include:

Brood mare: early lactation, late lactation, maintenance that includes anestrous and the first 8 months of gestation, the 9th month of gestation, the 10th month of gestation, and the 11th month of gestation

Growing horse: suckling, weaning, yearling, long yearling, 2-year-old

A sample growth rate is plotted in Figure 24-2.


The Brood Mare

Lactation Parturition is an extremely stressful event for mammals. As she recovers from the activities of foaling, the mare's appetite is usually depressed. At the same time, her mammary glands begin producing nutrient-rich colostrum. A primary goal after parturition will be to manage the mare so that she regains a healthy appetite. Mares are often fed a warm mash made of wheat bran and water to stimulate appetite at this time. Wheat bran has the added benefit of being a mild laxative. Generally mares should be gradually introduced to the lactating diet over a period of 7 to 10 days.

Aside from the short-duration muscular effort of the working horse, lactation requires the greatest amount of energy in the horse production cycle. In addition, the manufacture and secretion of milk increases the mare's requirement for other nutrients.



Maintenance/Early Gestation

An idle, mature horse and a mare in the first three quarters of gestation are animals that use feed nutrients only for maintenance functions. Once these animals achieve the desired body condition score (BCS) of 5 or 6, they should receive diets that support only maintenance. On maintenance diets, they will neither gain nor lose weight; they will be consuming just enough nutrients to maintain the status quo. Balancing rations for idle horses can be as challenging as balancing rations for horses with higher nutrient requirements. A diet based on early-cut grass hay or alfalfa hay cut at an early bloom stage of maturity will often contain energy, protein, and calcium nutrients in excess of these animals' requirements.

Environments that increase the loss of body heat will result in an increased maintenance energy requirement. In areas with extreme winters, it may be desirable to feed mares in mid-gestation excess energy to increase tissue insulation (BCS of 6 or higher). The companion application to this text considers five determinants of body heat loss: environmental temperature, night cooling, wind speed, external insulation (hair coat), and tissue insulation (body fat). Based on inputted values, adjustments are made on predicted dry matter intake (DMI) and the energy requirement.

A well-managed pasture, water source, and appropriate mineral supplement available free choice should be able to support the nutritional needs of one idle horse per acre. On pastures that are not managed, and during times of drought, it may take four or more acres to support the nutritional needs of one idle horse.

Horses described as "easy keepers" appear to have reduced maintenance energy requirements. Easy keepers appear to maintain or gain body weight when fed the diets that cause hard keepers to lose weight.

Gestation, Months 9 to 11

Nutrient requirements increase rapidly during the last 3 months of gestation because 60 percent of the neonatal foal's body weight is gained during this period. These requirements must be met without excesses to ensure that the foal's birth weight is acceptable and that the mare's body condition is maintained.

In late gestation, the appetite of mares will usually be somewhat depressed. This means that it may not be possible to meet her increased nutrient requirements with increased pounds of the maintenance diet. Ration nutrient density will have to be increased. Alfalfa hay cut at an early bloom stage will likely be useful in balancing rations for mares in late gestation, as will grains and other concentrated sources of nutrients.

The Stallion

The stallion should be fed a diet that is matched to his activity. Idle stallions in good body condition should be fed a diet that supports maintenance only. During the breeding season, the stallion's daily requirements for nutrients are 25 to 50 percent higher than the maintenance requirements, according to the horse NRC (1989).



The structure of the mare's placenta is described as epitheliolchorial. This type of placenta does not allow antibody immunoglobulins to pass from the mare into the blood of the fetal foal. These antibody immunoglobulins are acquired by the neonatal foal through colostrum. Colostrum or first milk, is secreted by the mare the first few days following foaling. It is different from ordinary milk in that it is a more concentrated source of nutrients and has a laxative effect, which aids in the passing of the meconium (the fecal material that accumulates in the large intestine during prenatal growth). Most important, however, colostrum contains antibodies. Colostrum should be consumed by the neonatal foal as soon as possible. Colostrum is discussed in Chapter 20. Foals too weak to nurse should receive colostrum by stomach tube. The quantity of colostrum needed will range from 1 to 6 pints (1 pint equals approximately 1 pound), depending on the quality of the colostrum and how many hours have passed since foaling.

If the mare is well fed, her milk should provide all the nutrients needed by the foal for the first 3 months. Many owners will make the weanling grain available to the suckling foal beginning at about 1 to 2 months of age. Doing so will ease the transition at weaning. The foal is usually weaned at 4 to 6 months, and at this age it will be eating 5 to 8 lb. of the weanling grain if it has been available. In addition to grain, the foal should be offered hay free choice.


At 2 months of age, the foal is usually interested in supplementing milk with other sources of nutrients. By 6 months of age, milk will play a minor role in supplying needed nutrients if the foal has been offered grain and hay. Foals are generally weaned at 4 to 6 months, and the stress of weaning can be minimized if the foal has been introduced to grain starting at 1 to 2 months of age.

Weanling foals should be fed balanced diets that supply enough nutrients to support a reasonable rate of gain. Generally, this means that grain is fed at no more than 10 lb. and hay is fed to achieve satiety. Weanlings sometimes tend to sort through a grain mix, consuming only the more palatable feedstuffs. Sorting can be prevented by using feed in pelleted form.

Yearling, Long Yearling, and 2-Year-Old

The proper development of the skeletal system is perhaps more critical in horses than in other species because horses are used for work and athletic activity. Calcium and phosphorus are the two primary minerals that make up the skeleton and their levels in the diet must be carefully managed. Magnesium is also an important constituent of bone.

The bioavailability of calcium in feed for horses ranges from 50 to 70 percent, whereas the bioavailability of phosphorous is about 30 to 55 percent. Bioavailability is a function of mineral source, and also declines with the age of the horse. The calcium requirement published by the horse NRC (1989) assumes that the feedstuffs supplying calcium are 50 percent bioavailable. The phosphorus requirement published by the NRC assumes that the feedstuffs supplying phosphorus are 45 percent bioavailable for lactating mares and growing horses, and 35 percent for all other classes of horses. The higher value for the lactating mares and growing horses is used because it is assumed that these animals will be receiving a significant amount of their phosphorus in the more bioavailable, inorganic form. The only other mineral for which the NRC uses predicted bioavailability in determining requirements is magnesium. It is assumed that magnesium is 40 to 60 percent bioavailable. The NRC uses the 40 percent value in determining requirements. These assumed bioavailabilities are applied by the NRC as safety factors in predicted requirements; the companion application to this text uses these same values.

Energy requirements for growing horses are given in the NRC nutrient requirement tables based on whether the expected growth rate is moderate or rapid. The energy requirement for growing horses is calculated more precisely in the text of the NRC publication. Rather than use qualitative inputs of growth potential, the text presents a formula that contains a variable of average daily gain; this formula is used in the companion application to this text.

As the horse grows, dry matter/feed intake increases and the required nutrient density in the diet declines. Rations need to be reformulated periodically during growth because excess nutrient levels may result in a rate of growth that negatively impacts soundness and longevity. This issue is discussed later in this chapter under the topic developmental orthopedic disease.


The Working Horse

Adult horses must be fed a diet that will support maintenance. Nutrient levels beyond maintenance will be necessary if the horse is used for work. In the horse NRC (1989) and in the companion application to this text, horse work levels are described as light, moderate, or intense. Light work examples include pleasure riding, bridle path hack, and equitation. Moderate work examples include ranch work, roping, cutting, barrel racing, and jumping. Intense work examples include race training and polo. Draft horses doing heavy work should be described as light if work is less than 3 hours, moderate if 3 to 6 hours, and intense if greater than 6 hours daily. The NRC formulas and those in the companion application to this text increase the requirement for digestible energy above maintenance by 25 percent, 50 percent, and 100 percent for light, moderate, and intense work, respectively.

Because of the high need for energy, horses at intense work may not be able to maintain body condition on a 50:50 forage-to-concentrate diet. Under such conditions, horses may benefit from added fat in the diet (Taylor, Ferrante, Kronfeld, & Meacham, 1995). It will also be best to offer some hay before the grain and to feed at least three times daily.

Working horses may lose significant amounts of electrolytes in sweat. The most important electrolytes contain sodium, chloride, and potassium. These mineral ions are not stored by the body and must be replenished daily to prevent problems with muscle function and fluid balance. The best way to replenish them is in small, frequent feedings. Endurance horses competing in long distance races should be given small amounts of a supplement containing electrolytes throughout the competition.

Sweat also contains water but in order to minimize the risk of water founder, hot, tired horses should not be given free access to cold water. These animals should get all the water they desire, but it should be made available in small quantities, offered at 10-minute intervals.

Fermentation in the Large Intestine

The large intestine provides a favorable environment for the bacterial fermentation of material that was not digested and absorbed in the stomach and small intestine. Available carbohydrates including fiber are broken down by the bacteria inhabiting the large intestine into volatile fatty acids (VFA), primarily acetic acid (acetate) and propionic acid (propionate), which may then be absorbed through the wall of the large intestine and utilized by the various tissues as sources of energy (Bergman, 1990; Hintz, 1983). For horses at maintenance, the VFA from fiber fermentation, together with the small amount of nonfiber carbohydrate and other organic compounds in forage, may satisfy the entire energy requirement, so these animals may not require grain.

Amino acids are made by the microbes inhabiting the large intestine of the horse. These amino acids become the protein in microbial cells. Whereas in ruminant animals the digestive processes of the true stomach (the abomasum in ruminants) and small intestine are downstream from the site of microbial protein production, the digestive processes are upstream in the horse. The microbes growing in the horse's large intestine are never exposed to the digestive processes. Neither do they pass through the small intestine, the primary site of amino acid absorption. It is, therefore, unclear how much of the microbial protein that is produced in the horse's large intestine becomes available to the horse.

The B vitamins and vitamin K are also formed during the microbial activity in the large intestine of the horse. As with microbial protein, a large portion of these synthesized nutrients end up in the manure because the large intestine does not absorb vitamins efficiently (Hintz, 1983). Many of the B vitamins function in energy metabolism, and it is reasonable to assume that horses with high energy requirements would have an increased need for B vitamins. Whether or not usual diets for heavily worked horses would be improved by supplementation of these nutrients is unknown.

Given the uncertainty regarding availability of the nutrients synthesized in the horse's large intestine, it would be prudent to feed a high-quality source of protein as the primary source of protein to growing horses. Regarding the B vitamins and vitamin K, feed the highest quality forage on hand to the growing horses. Avoid feeding diets to any horse that would be totally devoid of these nutrients, such as those consisting exclusively of overly matured, bleached hay.

Because the capacity of the horse's digestive tract is relatively small, a large meal has a relatively rapid rate of passage. A rapid passage rate may result in incomplete digestion in the stomach and small intestine. Incompletely digested feed material arriving at the large intestine has the potential to cause problems in the horse. Colic may result (colic is discussed later in this section). It is theorized that a disruption of the microbial populations may occur when large amounts of starch arrive at the large intestine, and that this may lead to the release of endotoxins. These endotoxins may play a part in the etiology of founder or laminitis (founder is also discussed later in this chapter).

Group Feeding

Ideally, pastured horses that must receive supplemental grain to balance the ration are brought into separate stalls at feeding time. If this is not practical, horses should be grouped according to nutrient need, and the grain can be offered to the group in such a way as to minimize fighting. Table 12-5 gives recommendations on feeder spacing when feeding grain to horses on pasture. If pasture is not providing adequate forage, it may be necessary to feed hay to the group. Because of increased waste, it will be necessary to feed about 20 percent more hay than the animals are expected to eat when hay is fed to pastured horses.

General Feeding Guidelines

All feed-related health problems in horses, including colic, could be prevented by providing a constant and consistent flow through the digestive tract of wholesome feed and water in an amount that satisfies the horse's appetite and thirst, and results in the absorption of nutrients at the level required by the tissues.

In striving to achieve this ideal nutritional management, the following practical feeding guidelines should be followed:

1. Keep feed boxes clean.

2. Make feed changes, especially carbohydrate changes, gradually. An overload of carbohydrate has often been implicated in the etiology of digestive disturbances in the horse such as colic and laminitis. There may not be a single carbohydrate component that is responsible for the overload in all cases. The hydrolyzable carbohydrate in "sweet feed" may be the agent involved in carbohydrate overload, but the nonhydrolyzable, rapidly fermentable carbohydrate of spring pasture may also cause carbohydrate overload in horses (Hoffman,Wilson, Kronfeld, Cooper, Lawrence, Sklan, & Harris, 2001). Avoiding carbohydrate overload is accomplished by adapting the horse's digestive system to changing feed carbohydrates and feeding frequently.

3. Feed frequently. Horses on pasture will spend at least half the day eating and meals will be fairly evenly spaced throughout the day. Stabled horses should be fed at least twice a day, preferably three times. Frequent feedings will help prevent colic and reduce the chances of the horse developing stable vices such as wood chewing and cribbing.

4. Always feed at the same time of day. Regularity in feeding programs helps avoid feeding problems.

5. Feed by weight, not volume. Oat grain is notoriously variable in density. A 1-quart container filled with oats of high-hull content may weigh 0.7 lb., whereas a quart container filled with oats of low-hull content may weigh more than a pound. A1-quart container filled with corn grain weighs 1.8 lb.

6. For those horses that tend to bolt their feed, make an effort to slow down their rate of consumption. Strategies include:

a. placing baseball-sized stones or chunks of block salt in the feeder

b. using a large box and spreading the feed

c. mixing chopped hay with grain in the feeder

7. Know the role of bulk in the diet. Bulk is necessary for effective performance of the digestive tract. However, it may be necessary to minimize bulk in the meal taken before heavy work.

8. When necessary, bring body condition down gradually.

9. Have fresh, clean water available at all times. Control water intake of a "hot" horse. Encourage horses to drink water before feeding.

10. Check teeth regularly to ensure that the horse can properly chew its feed.

11. Feed rations that contain appropriate levels of all required nutrients.


Generally, the term colic refers to the symptoms that are due to adverse conditions within the digestive tract. Such conditions accompany almost every systemic disorder of the horse. Colic, therefore, is not a symptom of a specific disease.

Horses with colic show general signs of anxiety, and may bite or kick at their abdomen, groan, or roll. Colic may be mild and the problem may resolve itself, or the problem causing colic may be life-threatening.

Listed below are problems that cause a horse to show symptoms of colic that involve feeding management.

1. Feeding unwholesome feedstuffs and feeds can cause a horse to show symptoms of colic.

2. The tendency of some horses to bolt their feed can lead to colic if such behavior is not properly managed.

3. Overfeeding is a common cause of colic.

4. Improper feeding management can contribute to constipation that will lead to colic. Providing the horse with a balanced ration and water will usually prevent constipation. A wheat bran mash is often fed to horses to prevent constipation. It should be recognized that the effectiveness of this feedstuff in preventing constipation has nothing to do with its nutritional content, but rather with its ability to soften the feces (a laxative effect).

5. An irregular feeding schedule can cause colic in some horses. Confined animals look forward to feeding time with great anticipation. Physical changes take place within the digestive tract as feeding time approaches. It is a fundamental principle of animal husbandry that animals be able to rely on the predictability of the feeding activity.

6. The sequence of component feeding will affect the completeness of digestion, and incomplete digestion may be a contributing factor to colic. Ideally, hay and grain are fed and consumed together. If this is not possible, hay should be fed first. Hay is more effective than grain in stimulating the flow of saliva and gastric juices, and this should set the stage for a more complete digestion of subsequent feedstuffs. In addition, hay passes through the digestive tract relatively slowly. The passage of grain will be delayed by the presence of hay in the digestive tract, resulting in more complete digestion. Grain that is incompletely digested in the stomach and small intestine may disrupt microbial populations when it arrives at the large intestine, resulting in carbohydrate overload and causing colic.

7. Horses that are fed only one large meal per day will be susceptible to colic. The digestive anatomy of the horse is designed for more or less constant processing of small quantities of feed. Figure 2-4d indicates that the stomach, the primary feed storage organ, represents only 9 percent of the volume of the digestive tract. When compared with the pig's 26 percent, the dog's 63 percent, and the ruminant's 67 percent, it is apparent that the horse is not designed to consume large meals that can be stored for later processing. Add this to the fact that the bile made by the horse's liver is not stored in a gall bladder but rather is constantly secreted directly into the intestine, and it becomes apparent that horses are not designed to process large, infrequent meals. A horse fed a single meal daily will eat rapidly. Ingested feed will pass rapidly through the digestive tract, leading to incomplete digestion.

8. Diet changes that are made without an appropriate transition can result in colic. As the availability and/or economic characteristics of feed resources change, the horse's diet should change. Also, as the horse's nutrient requirements change, the nutritional content of the diet should change accordingly. Ideally, these diet adjustments involve a reformulation so that the appetite of the animal is always satisfied when it receives the required amounts of nutrients. Drastic feed changes without a proper transition will often result in colic. When minor changes in the diet are called for, the transition to the new diet should be made over a period of several days. Major changes in the diet should be made gradually over a period of 2 to 3 weeks. When feeding a thin but otherwise healthy animal, take into consideration the fact that changing from a ration that is deficient in nutrients to a ration that meets nutrient requirements is still a ration change. Any ration change needs to be made gradually to minimize the risk of indigestion or colic.

9. Unlike ruminants, horses cannot regurgitate swallowed feed and they cannot eructate gases produced during fermentation. Because they cannot regurgitate, horses must chew their feed thoroughly before swallowing. Because horses cannot eructate, gases formed during fermentation can only be passed through the rectum. If excess gases are produced in the digestive tract, distension of the gut can interfere with blood circulation and respiration. The first eight causes of colic discussed in this section, along with #12 which follows, may result in excess gas formation.

10. The availability of water relative to the availability of feed can sometimes be a contributing factor to colic. Most horses drink rapidly, and if this flow of water washes large amounts of incompletely digested feed material into the intestine, colic may result. This problem is usually prevented by making water available to the horse during meals.

11. The horse's work schedule should be developed around feeding times to avoid colic. The distribution of blood in the body changes depending on what tissues in the body have the greatest need for delivery of oxygen and nutrients and the removal of wastes. The muscles of an exhausted horse will continue to hold priority status for the blood supply for a period of time after vigorous exercise, and the digestive tract will not be capable of processing feed until after a period of rest. Small amounts of water may be given at frequent intervals, but feed should be withheld for about 2 hours after vigorous exercise to avoid colic.

12. Conversely to number 11, if an animal has just been fed a large meal, it should be given time to digest it before being exercised. When feed is being digested, the animal's digestive muscles and glands are active. This activity is supported by an increased blood supply to the digestive tract. Hard work will divert blood to the skeletal muscles at the expense of the digestive organs. Incomplete digestion will result. Incompletely digested feed arriving at the intestine may result in colic. Another reason to avoid working a horse immediately after a meal has to do with its affect on the respiratory system. Immediately after a meal, the digestive tract is distended. The abdominal cavity occupies more space at the expense of the thoracic cavity, and the lungs are prevented from expanding to their fullest. Such a horse may experience difficult breathing during heavy exercise.

Laminitis and Founder

Laminitis is defined as an inflammation of the laminae of the feet. Laminitis has several causes. Founder is the term describing laminitis caused by a disturbance originating in the digestive tract.

The inflammation that characterizes founder is caused, in part, by the effects of histamine on the circulation of blood and lymph in the feet. Histamine is useful in the body when a wound or injury requires additional blood factors for repair activity. This is because histamine increases localized blood flow, which is evident as a swelling in the affected area. But the effects of histamine in the foot tissues cause pain and potentially permanent damage.

What conditions lead to an increase in the level of histamine in the foot tissues? Recall from Chapter 20 that in ruminant animals, an acid condition in the rumen leads to the establishment of a population of bacteria that convert the amino acid histidine to histamine, which is absorbed, contributing to laminitis in these species. The source of the histamine that contributes to laminitis in the horse may be the horse's own tissues, acting in response to the presence of endotoxin, as during enterotoxemia.

Enterotoxemia may be caused by starch overload. The resulting disruption in normal microbial populations of the digestive tract may cause the proliferation of undesirable bacteria of the genera Clostridium and Escherichia. If endotoxins produced by these bacteria are absorbed, enterotoxemia results. Enterotoxemia may also be caused by indigestion or by drinking cold water while the horse is still hot from exercise.

Another form of founder, called grass founder, occurs when horses that have spent the winter months working and consuming a high-grain diet are suddenly turned out on lush spring grass. As is likely to happen with any sudden dietary change, the horse experiences a dramatic gastrointestinal upset. In the case of grass founder, this leads to enterotoxemia, histamine release, and laminitis.

Investigations are being conducted to examine the possibility that the histamine that leads to laminitis in horses originates in the digestive tract, produced by bacteria and absorbed into the blood (Garner, Flint, & Russell, 2002). This etiology is more in line with what has been found by ruminant researchers.


Azoturia (also known as paralytic myoglobinuria and equine exertional rhabdomyolysis) occurs most often in the physically fit horse whose ration is balanced to satisfy the nutrients needed during intense work. The problem begins when such a horse is given a rest period of one to several days, but is still fed as if it was at work. When the horse commences physical exertion, the muscles cramp and the animal is unable to move.

During the course of azoturia, there is extensive damage to muscle tissue. In addition, there may be kidney damage and paralysis.

Azoturia can be prevented by maintaining a balance between diet and exercise. Once a horse has begun a rigid training schedule, that schedule and its corresponding daily ration must be maintained and carefully managed to ensure that changes are made gradually.


Heaves, or alveolar pulmonary emphysema, is a respiratory condition in horses. As with ordinary emphysema, the lung alveoli are damaged and the animal has difficulty breathing. Heaves appears to have several causes. Heaves may be a complication from a severe or neglected case of infectious respiratory disease. Heaves may also be the result of a reaction to inhaled particulate matter.

The feed is one of many potential sources of airborne particulate matter (dust) in a horse's environment. The most potent source of dust in most horse diets is the hay. The source of the dust may be fine particles of hay itself, or it may be mold that is growing on the hay. If the source of dust is mold, the hay should not be fed. When feeding hay, there are several actions that can be taken to reduce its dustiness. It can be shaken outside the barn. The dustiness of hay may be minimized by moistening it or pouring diluted molasses over it. As always, the feeder should be cleaned between feedings.

If hay is a problem for the horse with heaves, there are several hay modifications and alternatives that may be used. Hay baled at a higher moisture content than the usual 12 to 15 percent will be less dusty and perhaps more desirable for the horse with heaves. A mold inhibitor such as propionic acid must be used to prevent mold growth and spontaneous combustion of hay baled at greater than 15 percent moisture. Propionic acid treatment of hay does not affect the palatability of the hay. Cubed, pelleted, or fermented forage (silage) will be less dusty than long hay. Forage alternatives such as beet pulp may be fed. During the grazing season, hay in the diet may be replaced with pasture.

Feeding management can be altered to help minimize symptoms of the horse with heaves. The chances that irritants will enter the nasal cavity willbe reduced by allowing the horse to feed from the floor rather than from a hay rack. Again, it is critical that the feeding area be cleaned between feedings.

Body Condition Scoring

Body condition scoring of horses is based on a 9-point scale as shown in Table 24-1.

Prussic Acid Poisoning

Under certain conditions, some grasses, particularly forage sorghums, may accumulate hydrocyanic acid (prussic acid) in their tissues. Prussic acid poisoning is discussed in Chapter 20.

Endophyte-Infected Grasses

An endophyte is a fungus that lives inside a grass plant. The two organisms are involved in a symbiotic relationship in which the fungus receives a place to live in return for providing the plant with increased resistance to environmental stresses such as attack by insects.

Consumption of endophyte-infected tall fescue, whether in pasture or hay, may result in "tall fescue toxicosis." Tall fescue toxicosis impacts health, production, and reproduction in livestock (Waller & Fribourg, n.d.), especially horses. The effects on reproduction include:

* Lower conception rates

* Abortions

* Prolonged pregnancy

* Dystocia

* Retained placenta

* Higher rates of neonatal foal death

* Agalactia or poor milk production

The nonreproduction effects of tall fescue toxicosis on livestock include:

* Increased risk of laminitis

* Loose feces

* Reduced growth rate

* Reduced dry matter intake

Because most of the problems associated with consumption of endophyteinfected tall fescue are related to reproduction, one recommended measure is to remove the source of endophyte-infected tall fescue from the brood mare diet 60 to 90 days prior to foaling (Coleman, Henning, Lawrence, & Lacefield, n.d.). Endophyte-free tall fescue seed is available for those considering pasture renovation.

Plants other than tall fescue can become infected with endophytes. Rye-grass may be infected with an endophyte, and livestock consuming infected ryegrass may show muscle system symptoms such as incoordination and tetany. This disorder is called ryegrass staggers.

Feedstuffs Affecting Urinary Tract Health

Cystitis is inflammation of the bladder. It is characterized by painful, frequent urination and sometimes by bloody urine. Consumption of forage sorghum, Sudan grass, and sorghum-Sudan grass hybrids have been associated with cystitis or inflammation of the bladder in horses.

Because excess dietary protein leads to increased urea filtration by the kidneys, it used to be thought that high-protein feedstuffs such as early-cut alfalfa could cause kidney damage. It is now known that healthy kidneys are not damaged by the consumption of high-protein feedstuffs.

Developmental Orthopedic Disease

Developmental orthopedic disease (DOD) is a general term for several problems associated with improper development and maturation of the horse's skeleton. Nutrition, genetics, and endocrine function all may play a role in DOD.

The increasing incidence of developmental orthopedic diseases in horses has been attributed to feeding young horses for maximal growth (Ropp, Raub, & Minton, 2003). Mineral imbalances including copper deficiency may also cause DOD.

A nutrition--hormone interaction due to infrequent feeding may result in DOD (Hintz, 1995). Infrequent feeding results in insulin spikes that may cause a reduction in thyroxine (a hormone from the thyroid gland) production. Proper thyroxine levels are necessary to ensure normal maturity of the skeleton.

Nutritional Needs of the Geriatric Horse

Many feed manufacturers market feed formulations specifically designed for the geriatric horse. Some of the characteristics of these feed products include:

* Greater attention to grain processing, assuming some deterioration in the teeth of older horses

* Reduced fiber and increased nutrient density, assuming that older horses have reduced digestive efficiency

The horse NRC (1989) does not give specific nutrient recommendations for the geriatric horse.

Feedstuffs Used in Horse Diets

The choice of which feedstuffs to use in formulating horse diets will depend on four factors.

1. What works to balance the ration

2. Feedstuff cost and availability

3. Feedstuff palatability

4. Feedstuff acceptability

Low palatability may be an inherent characteristic of the feedstuff, but palatability may also be influenced by moisture content and contaminants such as molds and toxins. Palatability may also be affected by the physical condition of the feedstuff such as fineness of particle size. The acceptability of feedstuffs may vary, depending on the condition of the individual horse. For example, rations for horses afflicted with the respiratory ailment heaves should not be made with dusty feedstuffs unless efforts have been made to contain the dust.


1. Give three techniques that may be used to slow feed consumption in horses that tend to bolt their feed.

2. Give three strategies that can be used to ameliorate heaves caused by components of the diet.

3. Discuss the microbial activity that takes place in the horse's large intestine as it impacts the need to include dietary sources of B vitamins.

4. What happens to the horse afflicted with azoturia? How can it be prevented?

5. At what month of gestation do the nutrient demands of pregnancy begin to materially affect the mare's nutrient intake requirements?

6. What impact does a full digestive tract have on the ability of the horse to rapidly and fully expand the thoracic cavity as would be necessary during work or exercise?

7. Describe a horse with a BCS of 2. Describe a horse with a BCS of 5. Describe a horse with a BCS of 8.

8. What is an endophyte and what is its relevance to feeding horses?

9. Describe how to manage mineral nutrition to prevent developmental orthopedic disease.

10. Give five feeding management practices that may result in colic in horses. Give one horse behavior that may result in colic. Give one feedstuff that, when consumed by a horse, may cause colic.


Bergman, E. N. (1990). Energy contributions of volatile fatty acids from the gastrointestinal tract in various species. Physiological Reviews. 70, 567-590.

Coleman, R. J., Henning, J. C., Lawrence, L. M., & Lacefield, G. D. (n.d.). Understanding endophyte-infected tall fescue and its effect on broodmares. Retrieved 10/30/2003 from:

Garner, M. R., Flint, J. F., & Russell, J. B. (2002). Allisonella histaminiformans gen. nov., sp. nov. A novel bacterium that produces histamine, utilizes histidine as its sole energy source, and could play a role in bovine and equine laminitis. Systematic and Applied Microbiology 25, 498-506.

Hintz, H. F. (1983). Horse nutrition, A practical guide. New York: Prentice-Hall Press, Inc.

Hintz, H. F. (1995). Horses. In Basic Animal Nutrition and Feeding, 4th edition. Pond, W.G., Church, D. C., Pond, K. R. New York: John Wiley & Sons.

Hoffman, R. M., Wilson, J. A., Kronfeld, D. S., Cooper, W. L., Lawrence, L. A., Sklan, D., & Harris, P. A. (2001). Hydrolyzable carbohydrates in pasture, hay, and horse feeds: Direct assay and seasonal variation. Journal of Animal Science 79, 500-506.

National Research Council. (1989). Nutrient requirements of the horse (5th rev. ed.). Washington, DC: National Academy Press.

Ropp, J. K., Raub, R. H., & Minton, J. E. (2003). The effect of dietary energy source on serum concentration of insulin-like growth factor-I, growth hormone, insulin, glucose, and fat metabolites in weanling horses. Journal of Animal Science. 81, 1581-1589.

Taylor, L. E., Ferrante, P. L., Kronfeld, D. S., & Meacham, T. N. (1995). Acid-base variables during incremental exercise in sprint-trained horses fed a high-fat diet. Journal of Animal Science 73, 2009-2018.

Waller, J. C., & Fribourg, H. A. (n.d.). Performance of steers grazing pastures of endophyte-infected and endophyte-free tall fescue with and without clover. Retrieved 10/30/2003 from: ansci/pdf/Reports/performance.pdf
Table 24-1
Body condition score description in horses


Score   Spinous Processes           Ribs

  1     Little fat covering         Prominent
          spinous processes

  2     Some fat covering           Prominent
         spinous processes

  3     Fat buildup about halfway   Slight fat over ribs
          on spinous processes

  4     Slight convex ridge along   Faint outline of ribs
          back from ends of           discernible
          spinous processes

  5     Flat over back--spinous     Ribs not visible but
          processes buried            can be felt

  6     Slight concave ridge        Spongy fat felt
          along back                  over ribs

  7     Crease along back           Area between ribs
                                      filled with fat

  8     Crease along back           Difficult to feel ribs

  9     Obvious crease along        Patchy fat over
          back                        ribs


Score   Tailhead                    Withers

  1     Prominent and individual    Bone structure
          vertebrae evident           is evident

  2     Prominent and individual    Bone structure
          vertebrae faintly           faintly discernible

  3     Prominent but individual    Withers lean but bone
          vertebrae not evident       structure not apparent

  4     Fat can be felt around      Some fat apparent
          tailhead                    along withers

  5     Fat around tailhead feels   Withers rounded over
          spongy                      spinous processes

  6     Fat around tailhead feels   Some fat deposited
          soft                        along side of withers

  7     Fat around tailhead feels   Fat deposited along
          soft                        side of withers

  8     Fat around tailhead very    Area along withers
          soft                        filled with fat

  9     Fat around tailhead is      Bulging fat along
          bulging                     withers
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Author:Tish, David A.
Publication:Animal Feeds, Feeding and Nutrition, and Ration Evaluation
Geographic Code:1USA
Date:Jan 1, 2006
Previous Article:Chapter 23 Goat ration formulation.
Next Article:Chapter 25 Horse ration formulation.

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