Chapter 16 Feeding beef.
--J. RIFKIN, 1993
The nutritional phases in the beef production cycle, illustrated in Figure 16-1, include:
Brood cow: first trimester, second trimester, third trimester, postpartum period
Market animal Route #1: forage-based program
Market animal Route #2: grain-based program
A sample growth rate is plotted in Figure 16-2.
THE BREEDING HERD
The goals for the nutrition program of the beef cow herd include:
* Maintaining productive, healthy brood cows.
* Achieving conception in cows by 80 days postcalving to maintain a 12-month calving interval.
* Producing strong, healthy, neonatal calves.
To achieve these goals, lactating cows should be fed to make adequate milk to support calf growth. If the feed resources are deficient--as during a drought--the lactating cow may not make enough milk to support desired calf growth. In this case, creep feed may be appropriate. If the brood cow's body condition needs to be adjusted, the adjustment should be made toward the end of the first and throughout the second trimester.
Profitability in the brood-cow operation is largely determined by the producer's ability to manage the forage resource to meet the animals' nutritional needs. The usual forages include pastures and native rangelands, but preserved forages such as hay and corn silage are also used.
[FIGURE 16-1 OMITTED]
[FIGURE 16-2 OMITTED]
The brood cow's nutrient needs vary according to four phases: the first trimester, the second trimester, the third trimester, and the postpartum period. These phases are described in Table 16-1.
The cow nurses a calf throughout the first trimester. The first trimester begins when the nursing cow settles (becomes pregnant). It ends when the calf is weaned. Creep feeding is a management tool that impacts the nutritional programs of both the calf and the cow during the first trimester and beyond. Creep feed is nutrient-rich feed that is placed in a location so that only the calves have access to it. It is often placed near where the cows bed down. Meyers, Faulkner, Ireland, Berger, & Parrett (1999) describe many of the potential benefits of early weaning made possible through creep feeding. There are many issues that must be considered in deciding whether or not to creep feed calves:
1. A brood cow whose calf is creep fed will rebreed more quickly and require less feed to rebuild her body reserves if she lost weight during the time she was with the calf.
2. Creep fed calves will gain more weight by weaning than calves that are not creep fed.
3. The calf crop is more uniform in weight: calves of poor milkers eat more creep feed.
4. Creep feeding reduces weaning stress so weaning shrink (weight loss) is reduced.
5. Creep feed increases the cost of the brood-cow operation.
6. Heifers that are to be kept as replacements are usually not creep fed.
7. The price of calves in relation to the price of feed will determine profitability of creep feeding.
8. Creep feed is most likely to be economical when forage availability is low or of poor quality.
If creep feeding is used, it is usually started when the calf is 3 weeks old. The creep feeder should be located close to water, shade, and salt. Only 1 or 2 lb. of creep feed per calf should be placed in the feeder until the calves start to eat. Consumption will be approximately 1 lb. of creep feed per day for each 100 lb. of body weight. Feed must be kept fresh. The creep feeder should provide 4 inches of feeder length per calf (Table 12-5).
The needs of the fetal calf will not have an impact on the cow's nutrient needs during the first trimester. Toward the end of the first trimester, cow milk production decreases. As a result, calves will consume increasing amounts of forage. Cow nutrient requirements are relatively low toward the end of the first trimester. Adjustments of cow body condition are made most efficiently while the cow is still lactating toward the end of the first trimester.
When the calf is weaned, the cow's nutrient requirements are at their lowest level. Although cattle replenish body-fat reserves with greater energetic efficiency while lactating, from a management perspective, the second trimester is usually the easiest time to make adjustments in the cow's body condition.
The body condition scoring system is used as a means of assessing body fat reserves and overall energy status. For beef cattle, the system uses scores from 1 to 9 as described in the following chapter, in Figure 17-9.
Cows should calve with a body-condition score between 4 and 7, and ideally, animals are fed to achieve this level of body fat by the end of the second trimester and are managed throughout the third trimester to maintain it.
This is a period of increasing nutrient demand due to the developing fetus. Most of the birth weight of the calf is achieved during the third trimester of pregnancy. Failure to meet the cow's nutrient needs at this time may result in a reduced percentage calf crop: fewer of the brood cows will successfully produce a live and healthy calf. It may also result in a cow that has difficulty rebreeding.
In a spring calving program, the third trimester coincides with the winter season (Table 16-1). Cold temperatures will increase the cow's energy requirement if the environmental temperature falls below the animal's lower critical temperature (LCT). The LCT is the environmental temperature below which the animal will be unable to maintain body temperature through passive means. Below the LCT, feed energy will be repartitioned with a greater portion being oxidized to maintain body temperature and a reduction in energy available for other functions. The companion application to this text predicts the LCT given inputs regarding the animal's body size, body-condition score, hide thickness, hair coat, and energy intake. Adjustments in energy requirements are made if the inputted environmental temperature is below the animal's LCT. The third trimester ends at parturition.
The Postpartum Period
The postpartum period includes the time from parturition until the cow settles (conceives). In order for the operation to maintain a 12-month calving interval, the postpartum interval must be kept to no longer than about 80 days. This is because the gestation period is about 282 days and with a postpartum (open) period of much more than 80 days, it will take more than 365 days to complete the reproductive phases for production of a single calf.
Body-condition scoring is used to assess the amount of body fat available for mobilization in times of insufficient energy intake (Figure 17-9). Cows calving with a body condition score (BCS) of less than 4 will likely have an increased postpartum interval: the days to first estrus following calving. This delay will reduce the chances that these cows will be bred within the 80-day goal. Cows and especially heifers receiving inadequate nutrition during their pregnancy have poor reproductive performance in general (Randel, 1990). These animals show increased incidence of calving difficulty (dystocia), lowered conception rate, increased embryonic mortality, and decreased neonatal survival. The effects of inadequate nutrition during pregnancy are more severe in first-calf heifers than in older cows. At the other extreme, cows calving in fat condition (BCS over 7) are likely to have reduced conception rates.
After calving, the cow begins to lactate and will peak in milk production (11 to 27 lb./day, depending on the breed) within the postpartum period. The cow's greatest need for nutrients occurs during the postpartum period. Cows should be managed so that there are adequate forage resources available during this time. If fresh forage is not available, it will be necessary to feed preserved forages and perhaps a purchased energy supplement. Grazing cattle should receive a mineral supplement.
There are several ways to provide a supplemental source of nutrition to grazing cattle. Energy supplements may be hand-or limit fed. Hand feeding should be done during midday when cattle are not actively grazing so as not to disrupt normal grazing behavior. Also, it is important to be aware of dominance hierarchies in the cattle herd. First-calf heifers will be lower in dominance and will probably not receive any of a hand-fed supplement if they are not fed separately from the cows. Mineral supplements may be limit fed or fed free choice in the form of a loose mineral or a block. Free-choice liquid supplements can be formulated to contain energy, protein, mineral, or vitamin sources.
Some method of consumption control is necessary with free-choice supplements. A high level of salt or other substance is often added to alter palatability and limit consumption. When liquid feeds are offered through a lick tank, consumption may be controlled somewhat by adjustment of the wheel that delivers the liquid in the tank.
The postpartum period is often the time of greatest feed wastage. In a spring calving program, muddy conditions may result in feed losses of 40 percent or more of hand-fed supplements.
Beef Brood Cow Feeding and Nutrition Issues
Bloat or tympanites of the rumen occurs in ruminants when the gases produced during fermentation cannot be expelled through eructation. The gases causing the rumen distension in bloat are the usual products of bacterial decomposition of carbohydrates and proteins, primarily methane and carbon dioxide with small amounts of hydrogen sulfide and others. In severe bloat, the distension of the rumen pushes the diaphragm forward, making breathing difficult. In addition, the large veins of the abdominal cavity may be compressed, interfering with general circulation. Symptoms of bloat include swelling at the left flank above the rumen, arched back with feet drawn under the abdomen, staggering gait, labored breathing, and suffocation.
There are many factors involved in the etiology of bloat. Categories of factors include those associated with the feedstuffs consumed and those associated with the animal.
The feedstuff factors that may be involved in bloat are summarized in Figure 16-3. Whereas pasture bloat is associated with the consumption of legumes such as alfalfa and clover in a vegetative stage of growth, feedlot bloat is associated with the consumption of grain that has been finely ground.
[FIGURE 16-3 OMITTED]
The primary factor associated with bloat in pastured cattle is the legume content of pasture. The legumes are rapidly fermented by bacteria in the rumen. This rapid fermentation results in a bacterial bloom in the rumen, leading to a high rate of gas production and polysaccharide secretion by rumen bacteria. This polysaccharide is usually described as slime (Blood & Radostits, 1989). In addition, the rapid fermentation of legume plants leads to the generation of a large amount of small particles in the rumen. Bacteria attach to these small particles. The foam that prevents eructation is apparently produced by some interaction between the slime and the small particles with attached bacteria. The cation content of legume has also been implicated, as positively charged ions increase the stability of foam containing negatively charged proteins.
In terms of animal factors, some animals may have a genetic predisposition to bloat. Genetic factors that influence rate of feed passage and saliva composition and/or production could influence the incidence of bloat. Animals that are bloat-susceptible should be culled from the breeding herd.
Bloat risk can be minimized in animals that are to graze pastures containing legume by waiting until the legumes have attained a more advanced stage of maturity (bloom stage or later). Also, initial turnout should be delayed until midday when pastures are dry. By managing pastures to maintain no more than 50 percent legume, bloat risk can be reduced. However, selective grazing may result in animals consuming a greater proportion of legume than is present in the pasture. It is also helpful to provide a full feed of coarse hay prior to turning animals out to a pasture containing legume. Finally, pastures containing legume should be introduced gradually, and once transitioned, animals with unrestricted access to pasture will have fewer problems with bloat than those that receive intermittent access to pasture.
Feed additives that are used in bloat prevention generally are designed to reduce the production and stability of the foam that is preventing gas release through eructation. Detergents, surfactants, and vegetable oils have been used successfully in reducing the risk of bloat. Poloxalene, marketed as Bloat Guard, is a nonionic surfactant that acts as an antifoaming agent. Poloxalene is available in meal form to be mixed with grain. It may also be fed through blocks and liquid feeds, but because consumption of such feed sources is voluntary, the effectiveness of bloat prevention is reduced. Poloxalene is also available as a drench for emergency treatment of bloat. The category of antibiotics known as ionophores has been shown to have some value in reducing the incidence of bloat (Bagley & Feazel, 1989).
Environmental factors as they affect plant growth, changing rumen microbial species, and changing rumen microbial activity may also be contributing factors to bloat.
Grass tetany may occur in cattle that are grazing on grass pastures without appropriate mineral supplements available. Grass tetany is triggered by inadequate intake of bioavailable magnesium. The disorder is described in Chapter 9 (Magnesium, Signs of deficiency). It is especially prevalent in the spring when cattle are first turned out to lush pasture, and the challenge of prevention involves the logistics of providing grazing and free-ranging animals with a source of bioavailable magnesium. For these animals, supplemental magnesium is usually provided in a loose mineral fed free choice or a mineral block. The problem can also be prevented by intravenous injection of calcium and magnesium in the gluconate form.
Nitrate toxicity may occur in cattle that graze stressed pasture crops. Such stresses as cloudy weather, drought, and frost cause the plant to accumulate nitrate in the lower third of the stalk (nitrate poisoning is also called "corn stalk poisoning"). High levels of fertilizer application and herbicide treatment may also cause plants to accumulate nitrate. Suspected forage should be sent to a laboratory for analysis.
If absorbed, nitrate (N[O.sub.3.sup.-]) in the blood may cause kidney damage. In ruminant animals, however, consumption of forages containing high levels of nitrate usually results in microbial reduction of nitrate to nitrite (N[O.sub.2.sup.-]. If absorbed into the blood, nitrite converts hemoglobin to methemoglobin, which cannot transport oxygen. The symptoms of the usual nitrate poisoning in ruminants are really those of nitrite poisoning, which are those associated with asphyxiation (accelerated respiration and pulse rate), weakness, and trembling.
Crops that have accumulated nitrate may be safely fed as silage because the fermentation process chemically reduces some nitrates to gaseous nitrogen oxides. If ensiling is not an option, crops that have accumulated nitrate may usually be safely harvested for feeding by leaving a 12-inch stubble in the field. When feeding high-nitrate crops, the following precautions should be followed:
1. Feed a balanced ration (high dietary levels of readily fermentable carbohydrate increase the ruminant animal's tolerance to nitrate by increasing the efficiency of utilization of nitrogen by bacteria).
2. Feed smaller amounts of the high-nitrate feedstuff.
3. Multiple feedings of small amounts of the high-nitrate feedstuff will reduce losses from nitrate.
Water can also be an important source of nitrate. Water nitrate usually indicates surface pollution from fertilizers, manure, and/or sewage. As with forages, water suspected of nitrate contamination should be tested.
Tall Fescue Toxicosis
Beef animals that consume pasture or hay containing tall fescue that has been infected with an endophyte are susceptible to tall fescue toxicosis, which has various effects on health, production, and reproduction. Tall fescue toxicosis is discussed in Chapter 24. The causative agents involved in fescue toxicosis have been reviewed by Porter (1995).
Breeding Herd Replacements
The heifers that are kept as herd replacements are still growing and have different nutritional needs than the cows. As with the brood cows, replacement heifers use nutrients for maintenance. In addition to maintenance, replacement heifers will use nutrients for both growth and reproduction. The diets fed to replacement heifers must supply a level of nutrition that supports all active functions. For this reason and because they will be lower on the dominance hierarchy, they should be fed and managed separately from the cows.
Replacement heifers should be managed to have their first calf by 2 years of age. The calving period for this group should be restricted to 45 days or less. To achieve these goals, the replacement heifer group must be fed to grow uniformly so that the group attains puberty in time to breed at 13 to 141/2 months of age.
For heifers of typical beef breeds, including Angus, Hereford, Charolais, and Limousin, puberty is attained when animals reach 60 percent of their mature body weight. Use of ionophores in replacement heifer diets has resulted in reduced age at puberty (Bagley, 1993). Heifers of the dual-purpose or dairy breeds including Holstein, Brown Swiss, Braunvich, and Gelbvieh, should be fed to reach 55 percent of their mature body weight by breeding. With good management, these body weights correspond to 13 to 16 months of age. Because the gestation period is about 9 months (282 days), heifers bred at 13 to 16 months of age will calve at 22 to 25 months. To improve the chances for dropping a live healthy calf, bred first-calf heifers should be fed adequate nutrition during the gestation period to support the gain necessary to achieve 85 percent of mature weight by calving.
As an example, an Angus heifer's mature weight is 1,100 lb. Puberty is expected at 14 months (420 days of age) when she weighs about 60 percent of her mature weight (0.60 x 1,100 = 660 lb.). If weaning weight at 200 days of age is 4501b., the heifer should be fed to gain 660 - 450 = 2101b. for the period from weaning to breeding.
At weaning, she is 200 days old so she has 420 - 200 = 220 days from weaning to achieve her 660-lb. breeding weight. The Angus heifer needs to gain 210 lb. in 220 days, which translates to a rate of gain of 210/220 = 0.951b. per day.
In addition to the nutrient demands of pregnancy, heifers are growing animals. In our example, the first calf heifer should weigh 9351b. (85 percent of her mature body weight) at calving. In our example, the heifer was bred at 420 days so her age at calving will be gestation length + 420 or 282 + 420 = 702 days at calving. This translates to a gain from breeding to calving of 935 - 660 = 2751b. in 702 - 420 = 282 days. The necessary rate of gain from breeding to calving is 275/282 = 0.981b./head/day (Table 16-2).
Nutritional management of breeding herd replacements has been reviewed (Bagley, 1993).
Compared to growing/finishing cattle of similar body weights and rates of gain, growing bulls require 15 percent more Mcal of net energy for maintenance. Likewise, mature bulls require 15 percent more Mcal of NEm compared to cows. Other nutrient requirements are similar in comparable bulls and growing/finishing cattle. Note that the bull grows to a body weight that is 67 percent greater than the cow. Both underfeeding and overfeeding bulls will result in poor breeding performance.
The goal with weaned calves that are not intended to be kept as breeding herd replacements is to develop them into a product that may be profitably marketed. Generally, this means attaining a quality grade of Choice. Quality grade is based on the level and distribution of fat within muscle tissue, usually referred to as marbling. Choice quality grade is just below Prime at the top of the USDA grade standards for steers and heifers.
There are many systems for developing cattle into a product that attains a Choice carcass. Figure 16-1 illustrates two basic systems described as forage based and grain based. All systems share some features of these two basic systems. Generally, the forage-based system will require more days to achieve a quality grade of Choice than will the grain-based system. However, the grain-based system will require more purchased feed to achieve a quality grade of Choice. Generally, the heifer or steer in the forage-based system will achieve Choice at a larger body weight than the animal in the grain-based system. The decision of which system to use will be based on anticipated beef prices, availability of forage resources, and grain prices.
The finishing phase is common to many forage-based and grain-based systems. It is the final feeding phase before slaughter and it is largely responsible for the degree of marbling present in the carcass. In the finishing phase, cattle are fed a diet containing 85 to 100 percent grain, and the rate of gain is frequently greater than 3.5 lb./head/day. The companion application to this text predicts daily gain supported by both the levels of metabolizable energy and protein in the ration.
To prevent digestive problems in the finishing phase, a transition or "receiving program" is usually implemented. Although receiving programs vary, they all share the goals of acclimating cattle to bunk feeding and gradual replacement of forage with grain. If calves arrive at the finishing phase from a backgrounding or grower phase, many of the goals of the receiving program will have already been met. Some receiving diets will contain relatively high levels of antibiotics as prophylactic medication. These levels will be reduced or antibiotic feeding will be eliminated at the conclusion of the receiving period in 2 to 3 weeks. Many antibiotics have withdrawal periods and cattle must receive a diet free from these products for the duration of the withdrawal period immediately prior to slaughter. The transition from the receiving diet to the final finishing diet generally takes 2 to 3 weeks.
When cattle reach the final finishing diet, they are said to be on full feed. The grain of the finishing diet will usually be corn, milo, wheat, or barley grain. These grains may be fed dry or fermented, whole or processed. Grain is usually processed before feeding (Chapter 13). The effects of grain source and processing method on feedlot cattle performance has been reviewed (Owens, Secrist, Hill, & Gill, 1997)
The phenomenon of compensatory gain is frequently exhibited by cattle that arrive at the finishing phase from a forage-based system. The growth of such cattle has been suppressed due to poor forage quality and/or availability. On the finishing diet, these cattle gain faster, and in some cases, more efficiently than others of the same weight.
Urea is a common component of the finishing diet. Urea is a form of nonprotein nitrogen (NPN) as opposed to preformed plant or animal protein. Urea in the rumen is first hydrolyzed by microbial urease to ammonia. This conversion is relatively rapid and requires little energy. The nitrogen in the ammonia is then incorporated into the bacteria as amino acids in cell proteins. This incorporation is relatively slow and requires considerable energy.
Urea should not be fed to a ruminant animal at a level greater than what the microbes can use. The limiting factor is the level of fermentable carbohydrate in the diet. The fermentable carbohydrate yields the energy needed by the microbes to fully utilize urea. Diets containing only low-quality forage and no grain should not contain urea because, although urea will be converted to ammonia, incorporation will not occur and the ammonia may be absorbed, leading to toxic effects. Based on usual grain levels, one rule of thumb for urea use in growing/finishing rations is to limit it to a level of urea that supplies no more than one third of the total ration nitrogen (Taylor, 1994). Given the many different types of growing/finishing diets, the application of such rules of thumb is risky. The best way to determine the upper limit for urea in a given ration is to find that level beyond which no further increase in microbial growth is supported. To this end, the companion application for ruminants predicts the bacterial growth from degradable protein sources such as urea. The companion application also calculates the percentage of ration nitrogen from nonprotein nitrogen and the equivalent crude protein from nonprotein nitrogen when using urea in a blend of feedstuffs.
The protein that the microbes make from urea is composed of amino acids. Some of these amino acids contain the mineral sulfur. Sulfur may not be present in adequate amounts in finishing diets to make efficient use of urea and may require supplementation. The usual recommendation for the ratio of nitrogen to sulfur is from 10:1 to 12:1 for ruminant diets containing urea (Qi, Lu, & Owens, 1993). The companion application to this text displays the nitrogen-to-sulfur ratio as ruminant rations are developed.
A variety of additives are approved for use in finishing cattle. Feed additives are used to achieve many economically important effects including the improvement of feed efficiency, daily gain, the increase of carcass weight at Choice, and the reduction of incidence of some health problems such as coccidiosis, laminitis, acidosis, bloat, and liver abscesses. Approved additives include antibiotics, probiotics, and chemotherapeutic agents. Some products designed to improve feed utilization by cattle are administered as an implant beneath the skin rather than as a feed additive. Anabolic ear implants have been shown to increase dry matter intake (DMI) and body-weight gain, and improve feed conversion (Rumsey, Hammond, & McMurtry, 1992). Melengestrerol acetate (MGA) is a feed additive with similar effects. The primary use of these anabolic products is to increase rate of gain through protein and fat accretion. Implant use or no use is an input in the companion application to this text. When no implant is used, the application reduces predicted DMI by 6 percent. When an implant is used, DMI is not reduced and the slaughter weight at the chosen level of finish should be increased. Likewise, ionophore use or no use is an input in the companion application to this text. When an ionophore is used, the application reduces predicted DMI by 6 percent and applies a credit to the feed net energy for maintenance (NEm) value, increasing the ration NEm concentration by 12 percent. These adjustments are made based on recommendations in the NRC (2000).
Approved feed additives are found in the Feed Additive Compendium (2004), and these as well as implants are described at the Web site titled FDA Approved Animal Drug Products located at http://dil.vetmed.vt.edu/ NADA/default.cfm. The companion application to this text is linked to this Web site in the feedstuff blending section. A discussion of feed additives is found in Chapter 3.
Growing/Finishing Cattle Feeding and Nutrition Issues
Bloat in Feedlot Cattle
Though less common than in pastured cattle, bloat may also occur in growing/ finishing cattle. Although the diets of these two types of beef animals are obviously different, the characteristics of feedstuffs associated with bloat in feedlot cattle are similar to those that cause bloat in pastured cattle (Figure 16-3). In addition, the highly fermentable carbohydrate in feedlot diets results in the elaboration of acid that may reduce rumen pH. A reduced rumen pH may result in reduced rumen motility, allowing gasses to accumulate. The incidence of bloat in feedlot cattle may be influenced by the type of grain fed, as well as the type and extent of grain processing (Cheng, McAllister, Popp, Hristov, Mir, & Shin, 1998).
Polioencephalomalacia (PEM) is a disorder of sheep and cattle that appears to be caused by the ingestion of substances that create a thiamin deficiency. For ruminants, the source of thiamin is microbial activity in the rumen. Thiaminase enzymes can cause PEM by destroying thiamin in the rumen. Thiaminases are found in raw fish products, bracken fern (Pteridum aquilinum), field horsetail (Equisetum arvense), and others. PEM can also be caused if dietary factors encourage the growth of thiaminase-producing bacteria in the rumen. Such dietary factors are not well defined, but are associated with high-grain diets. Finally, PEM can be caused by ingestion of excessive sulfur-containing compounds, including excess sulfates in water. This may lead to the production of a thiamin analog, which, though it serves none of the thiamin functions, appears to replace thiamin in important metabolic reactions.
Calves, like lambs and kids, are subject to enterotoxemia (overeating disease) if stressed or poorly transitioned from a high-forage to a high-grain diet. Enterotoxemia is discussed in Chapter 20.
Acidosis and Related Disorders
Acidosis is an ailment that frequently afflicts cattle on finishing diets. Acidosis in this text is discussed in Chapter 20. Reviews of acidosis in finishing cattle have been made (Owens, Secrist, Hill, & Gill, 1998; Schwartzkopf-Genswein, Beauchemin, Gibb, Crews, Hickman, Streeter, & McAllister, 2003).
In the companion application to this text, rumen pH is predicted from the level of physically effective neutral detergent fiber (NDF) in the ration (Figure 18-4). Beef cattle that are continually challenged with low rumen pH are more likely to have liver abscesses. Damage to the rumen epithelium caused by excessive acid production allows pathogens to leave the rumen and enter the liver. Affected animals have reduced DMI[UN1] and feed efficiency and decreased carcass yield. Control measures generally involve feeding antibiotics. A description of the causes and options for control of liver abscesses has been reviewed (Nagaraja & Chengappa, 1998).
Like liver abscesses, laminitis is associated with the acidosis complex. Factors that predispose cattle to laminitis have been reviewed (Vermunt & Greenough, 1994).
As with swine, the use of repartitioning agents is an active area of research in the beef industry. Such agents have been reported to improve the efficiency of production of lean beef (Moloney, Allen, Ross, Olson, & Convey, 1990).
1. Discuss the pros and cons of creep feeding beef calves.
2. What mineral is associated with grass tetany?
3. What causes pasture bloat? What causes feedlot bloat?
4. Define lower critical temperature.
5. When can an increase in the brood cow's body condition be achieved most efficiently?
6. Explain how the nitrogen-to-sulfur ratio is applied to urea feeding. Why is the amount of urea that can be used by beef animals related to the amount of fermentable carbohydrate in the diet?
7. Explain why ruminant consumption of forages high in nitrates may result in poisoning due to nitrites.
8. What is the target weight, expressed as a percentage of mature weight, to breed Hereford and Angus replacement heifers? What percent of body weight should they reach by calving?
9. Describe the differences between a forage-based and a grain-based feeding program for beef cattle.
10. The following question pertains to conditions in the northern hemisphere. In a spring calving program, maximum forage availability corresponds with the first trimester of the brood cow. In a fall calving program, maximum forage availability corresponds with the third trimester of the brood cow. Discuss the advantages and disadvantages of each type of calving program.
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Table 16-1 Brood cow phases with spring and fall calving programs Cow's Need for Cow's Need for Forage Forage to Support to Support Calf Growth Phase/Season Fetal Growth through Lactation 1st trimester, Minimal Milk production is Spring calving: declining. Cow's early June need for nutrients Fall calving: is declining while early December calf's need for nutrients is increasing. 2nd trimester, Increasing, but Calf is weaned and Spring calving: still low put on a different early September feeding program. Fall calving: early March 3rd trimester, Maximal-90% of fetal Calf has been Spring calving: growth occurs weaned. early December during last 40% of Fall calving: gestation. early June Postpartum period, Cow is open (not This is the period of Spring calving: pregnant). maximum milk Mid-March production. Fall calving: Mid-September Forage Availability Characteristic of the Phase/Season U.S. Midwest 1st trimester, Spring calving: maximum Spring calving: forage availability early June Fall calving: Fall: minimal forage early December availability 2nd trimester, Spring calving: decreasing Spring calving: forage availability early September Fall calving: Fall: increasing forage early March availability 3rd trimester, Spring calving: minimal Spring calving: forage availability early December Fall calving: Fall: maximum forage early June availability Postpartum period, Spring calving: increasing Spring calving: forage availability Mid-March Fall calving: Fall: decreasing forage Mid-September availability Table 16-2 Approximate relationship between age and weight of beef calves Age (days) Weight (lb.) Weaning 200 450 Breeding 420 660 Difference weaning to breeding 220 210 Daily gain necessary-weaning to breeding 210/220 = 0.95 lb./day Calving 702 935 Difference breeding to calving 282 275 Daily gain necessary-breeding to calving 275/282 = 0.98 lb./day
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|Author:||Tisch, David A.|
|Publication:||Animal Feeds, Feeding and Nutrition, and Ration Evaluation|
|Date:||Jan 1, 2006|
|Previous Article:||Chapter 15 Swine ration formulation.|
|Next Article:||Chapter 17 Beef ration formulation.|