Feeding and Nutritional Management of the Beef Cattle Breeding Herd
Mature Cows and First-Calf Heifers
Optimizing nutritional management of forage-based cow-calf production systems requires synchrony between nutrient requirements and nutrient supply. Cows should be bred to calve and be rebred during times of greatest forage abundance and nutrient supply because this is when their nutrient requirements are the greatest. Operations that calve out of synchrony with forage abundance and nutrient supply require a relatively greater amount of supplementation and forage replacement, which may not be economically feasible in many situations.
Failing to meet the nutrient requirements of cows has economic consequences. Because cattle partition, or prioritize, the use of nutrients toward functions that are most important to their own preservation, reproduction is the first trait to be sacrificed during times of substantial energy and protein deficits. It is also impractical (and often not economically feasible) to meet 100% of the energy and protein requirements of the cow herd at all times. Rather, it is more practical and therefore a more obtainable goal to ensure that, each year, cows are capable of regaining 100% or more of their body's energy and protein stores lost throughout the productive year.
Images courtesy of Dr. Ky Pohler (1), Dr. Matt Hersom (2), Dr. Jason Smith (3–8), and Dr. Dan Eversole (9).
Cows should be managed to calve at a target body condition of 5–6 (on a 1–9 scale, where 1 is emaciated and 9 is morbidly obese), to increase their likelihood of rebreeding within a defined calving season and calving once per calendar year. Body condition score (BCS), when evaluated at the time of calving, is, in general, inversely related to the female's postpartum interval to return to estrus, or the amount of time required after calving to resume estrous cyclicity. The postpartum interval to return to estrus ultimately impacts the amount of time that is required for successful rebreeding.
As BCS at calving decreases, the amount of time it takes for the female to start cycling again and conceive increases. A cow that calves at a BCS of < 5 is far less likely to conceive again within the amount of time required for her to calve annually, compared to a cow that calves at a BCS of ≥ 5. If the forage resources and overall nutritional management program are unable to meet the energy and protein requirements of the cow, her “excess” condition will help fill the void and ensure productivity. However, if that excess condition doesn’t exist, she has no reserve to pull from, and reproduction suffers.
Evaluating body condition at set points throughout the year enables adjustments to feeding programs with ample time to make a difference. As a general rule of thumb, evaluating BCS around the time of calving and again around the time of weaning provides that opportunity. If the BCS is < 5–6 at the time of calving and forage resources are “fixed,” supplemental feeds that provide a sufficient amount of protein and energy to fill the void left by the forages should be considered. If forage resources are not fixed, purchasing a more nutrient-dense forage, or using pasture resources with higher quality or more forage, should be considered. Alternatively, confinement cow-calf systems that rely primarily on a total mixed ration to meet the nutrient requirements of cattle should target maintaining an ideal body condition of 5–6 throughout the productive year.
When standardized to account for differences in body weight, the protein and energy requirements of first-calf heifers are ~10%–15% greater than those of mature cows that have a similar mature body weight. First-calf heifers that are managed together with mature cows generally do not have their protein and energy requirements met, leading to poor reproductive performance and an increased culling rate. Therefore, it is highly recommended that first-calf heifers be managed, including being fed, separately from the mature cow herd. To meet their requirements, first-calf heifers should be supplemented or fed diets that provide ~10%–15% more protein and energy per unit of body weight than do the diets fed to mature cows. Alternatively, first-calf heifers can be allowed to graze the highest-quality forages available beginning at or soon after calving and lasting through the breeding season.
To achieve these goals and meet the nutrient requirements of the cow herd, it is important to recognize the changes in nutrient requirements throughout the productive year (see Dietary energy requirements, mature beef cow and Dietary crude protein requirements, mature beef cow), as well as the changes in forage abundance and nutrient composition throughout the growing season(s). Asynchrony between nutrient requirements and nutrient availability can often be corrected by adjusting calving and weaning dates or by increasing forage diversification through the addition of cool-season or warm-season forages that complement the existing forage base, through improved grazing management practices such as rotational grazing, or through supplementation.
Supplementation programs should be based primarily on nutrient need and supplement value (nutrient cost). Although most often considered for energy and protein supplementation, these same concepts apply to mineral supplementation. In hay-feeding situations, the results of a forage nutrient analysis should be used to design a complementary supplementation program that fills the nutrient void as economically as possible. Regular pasture forage nutrient profiling can also be used to develop a strategic supplementation program that complements the needs of grazed forages.
Some supplemental feedstuffs or supplementation practices may simply displace forage in the animal's diet; others may affect digestibility, disproportionately increasing or decreasing forage digestibility and, as a result, influencing forage intake to a similar extent. Some supplemental feedstuffs, such as those high in fat or starch, typically (but not always) decrease forage digestibility and intake; others, such as those high in protein, often (but not always) increase forage digestibility and intake. For these and many other reasons, it is recommended to consult with a beef cattle nutritionist to develop an optimal supplementation program.
A common misconception among producers is that overfeeding pregnant cows during late gestation will increase calf birth weight so much that the incidence of dystocia, or calving difficulty, will increase. Birth weight is quite resilient to this type of nutritional insult and remains relatively unchanged, at least to any meaningful extent. In addition, it is not possible to feed a cow enough to increase calf birth weight beyond the calf's genetic potential for birth weight. Underfeeding the pregnant cow, however, sets her up for failure during the upcoming breeding season because she will most likely enter it at a nutritional disadvantage. Nonetheless, care should be taken to avoid overconditioning pregnant cows to the point of obesity, because cows calving at a BCS of 8 or 9 may experience an increased incidence of dystocia as a result of accumulated internal fat, rather than a difference in calf size.
Failing to meet the dam's nutrient requirements during middle and late gestation can also have some major implications for calf health and growth performance. Energy status is the major factor that affects a newborn calf’s ability to regulate its body temperature and stay warm during cold weather. The newborn calf metabolizes most of the fat that was deposited throughout fetal development as a source of heat during the first 24–48 hours of life. Failing to meet the dam's energy requirements during middle and late gestation restricts the amount of brown adipose tissue that is available to the calf to metabolize soon after birth. A high prevalence of chilled calves is often caused by insufficient nutrition of the pregnant dam.
Colostrum is also affected by nutrition of the pregnant dam. Nutrient-restricted cows not only produce colostrum that is lower in quality, but they produce less of it. Insufficient colostrum consumption soon after birth can affect the calf for the remainder of its life, because the antibodies obtained from colostrum are required to populate its naive immune system. Insufficient gestational nutrition of the dam can contribute to the failure of passive antibody transfer in calves.
Mature Bulls
The nutrient requirements of bulls are considerably higher during the breeding season than during the off-season. Bulls are much more active during the breeding season, making their energy and protein requirements relatively high at that time. Similar to the lactational requirements of a cow, the quantities of nutrients required to meet the demands of a working bull are considerable. Nutritional management programs that are capable of meeting the nutrient requirements of lactating cows and allowing them to resume estrous cyclicity within a relatively short period of time are typically also capable of meeting the needs of a bull, assuming he was not malnourished or underconditioned before turnout.
Bulls typically lose body condition throughout the breeding season, so they should possess enough condition to support fertility without being overconditioned to the extent that fertility is negatively affected. As a general rule, bulls should be turned out in at least the same condition as cows, and preferably in a BCS that is 0.5–1 greater than that of the cows.
When placed in a management setting that does not meet the needs of the bull, his fertility will suffer if he does not possess adequate nutrient reserves to fill the void. After the breeding season, bulls should be managed to gradually replenish lost condition without overconditioning. Note also that mineral and vitamin nutrition are equally as important to the bull as they are to the remainder of the breeding herd, so mineral and vitamin supplementation programs should not be overlooked.
Newborn and Suckling Calves
Newborn calves have very high protein and energy requirements, which are fulfilled by milk. As calves age and grow, they begin to consume solid feed or graze pasture forage, and thus their major source of nutrients begins to shift from milk to other feeds. This shift in dietary composition is very important to the calf's development because it plays a large role in the development of rumen function. After full rumen function has been achieved, the rumen begins to act as a fermentation vat, which will play a critical role in the digestive process for the remainder of the calf's life.
In certain situations, supplemental feed may be offered to calves that are still nursing in order to increase growth rate and aid ruminal development. Typically, a creep feeder is used for this purpose. This apparatus excludes cows and other cattle that are larger than the calves from consuming its contents.
It is important to evaluate the economics of creep feeding because the return on investment may not always be positive. The creep concept, however, can also apply to grazing settings without supplementation of additional feedstuffs, where calves are allowed to graze higher-quality forages that cows cannot access. This type of management is commonly referred to as "creep grazing."
Weaned Calves
Calves are typically weaned (ie, milk is removed from the diet as a result of separation from the dam) at ~6–8 months old. Alternatively, in early weaning the calf is removed before this age. Early weaning can be used to temporarily decrease the nutrient requirements of the dam. This approach generally requires a shift in feeding management because early-weaned calves have higher nutrient demands than do conventionally weaned calves, and thus must be fed accordingly.
Regardless of age at weaning, a best management practice is to precondition weaned calves for 6 weeks or more before they are sold. During this time, calves should become acclimated to feed bunks and watering systems to ensure that they know how to eat and drink before they are moved to the next phase of production. Because milk has been removed from the diet, calves should be provided with free-choice access to high-quality harvested roughages, such as long-stemmed grass hay, or with the ability to graze pasture that contains high-quality forages.
During the preconditioning of weaned calves, small amounts of concentrate feeds or supplements can be introduced. Once calves willingly consume a small amount of the concentrate or supplement, the quantity offered can be gradually increased until the desired amount has been reached. Care should be taken not to overfeed calves during this period.
The importance of clean water cannot be overemphasized. Troughs or watering systems should be cleaned as often as necessary to ensure that cattle always have access to clean, fresh water.
Feeding and Nutritional Management of Growing Beef Cattle
Replacement Heifers and Developing Bulls
Once weaned, replacement heifers should be gradually developed to achieve ~65% of their estimated mature body weight at the time of breeding. Among all individuals within a given group of replacement heifers, this percentage may range from 55% to 75% of estimated mature weight.
To achieve this target, usually heifers must receive the nutrients necessary to gain ~1–2 pounds (~0.45–0.91 kg) per day of body weight between weaning and breeding. The goal can be met by forages alone during certain times of the year when heifers are actively growing. When forages are dormant, however, or when cattle are being limit-fed with harvested resources or are grazing crop residues, some protein and energy supplementation is required.
Replacement heifers should be managed separately from the mature cow herd to ensure that the necessary growth rates can be achieved without overfeeding or underfeeding the other cattle in the herd. Achieving the target growth rate will help ensure that most heifers reach sexual maturity, or puberty, and are cycling before the breeding season starts.
Compared to other stages, young developing bulls require greater amounts of energy and protein to support the growth necessary to reach sexual maturity. A deficiency in either energy or protein delays puberty and subsequently impacts fertility. Therefore, the preweaning nutrition of developing bulls is of utmost importance.
After the breeding season, heifers should be managed to grow at a rate necessary to achieve at least 85%–90% of their estimated mature body weight before they calve for the first time. This rate of growth helps ensure that the developing calf is not deprived of energy, and that the heifer does not accumulate excess body fat before calving.
It is important to avoid overconditioning replacement heifers and breeding bulls; however, it is also important to recognize that overconditioned cattle are typically more productive than underconditioned cattle. Replacement heifers should be managed to enter the breeding season at a BCS of ~0.5–1 greater than that of mature cows. For example, if the cows are entering the breeding season at an average BCS of 5, the replacement heifers should be developed to enter their first breeding season at a body condition score of 5.5 or 6.
Bulls should also be developed to enter their first breeding season at a body condition greater than that of mature cows. However, bulls that undergo intensive bull development programs or those that are otherwise overconditioned (BCS of ≥ 7) should be gradually adapted to the pasture conditions in which they will experience their first breeding season, or "hardened," before turnout.
The importance of mineral nutrition to developing replacement heifers and breeding bulls should not be overlooked. Mineral deficiencies can have substantial negative effects on fertility. If an animal is being fed a total mixed ration, care should be taken to ensure that the ration has been formulated to meet the animal's requirements for minerals and fat-soluble vitamins. If grazing, consuming hay, or feeding on other harvested roughage, cattle should either be provided free-choice access to a complete mineral supplement that complements the forage base of the ration or be given another supplement that contains the amount necessary to meet the animal's requirements.
Growing Cattle
One of the primary goals of growing and backgrounding programs is to achieve economical weight gain on feeder calves before they enter the finishing phase. Although average daily gain varies across different programs, typical targets are 1.5–2.5 pounds (0.68–1.13 kg) per head per day.
This weight gain goal is often achieved in growing cattle by grazing high-quality annual or perennial forages, and supplementing protein and energy as needed to achieve targeted levels of performance. In these situations, supplementation with feedstuffs that are relatively high in energy often returns more on the investment than does supplementation with a similar amount of feedstuffs that contain less energy and more protein. Calves grazing dormant pasture or range forages often benefit substantially from supplements that provide appreciable amounts of both energy and protein. Mineral supplementation to fill the void that is left by forage deficiencies promotes growth and feed efficiency, improves immune function, and decreases the risk of mineral-related conditions such as "grass tetany."
Backgrounding programs typically strive to achieve similar goals. The difference is that cattle are managed in a dry lot, and most of their nutrients are provided through a total mixed ration, concentrate feeds, or harvested roughages.
Feeding and Nutritional Management of Finishing Beef Cattle
Conventional feedlot finishing programs rely primarily on cereal grains, such as corn, to provide rations that are much more energy dense than the rations fed in any other production phase. Roughages are often minimized in these rations, provided only in amounts necessary to ensure rumen function and overall digestive health. Similarly, many finishing programs rely heavily on by-products of other industries as major feedstuffs, such as distiller's grains or corn gluten feed. Most of these operations are located in the Corn Belt and Great Plains regions of the US because of abundant access to cereal grains and their by-products, as well as environmental conditions conducive to feeding cattle.
Upon arrival at the feedlot, cattle are started on what is commonly referred to as a "receiving ration," which typically contains a relatively high amount of roughage (~35% of dietary dry matter). Common roughage sources include hays, silages, or harvested crop residues, such as cornstalks or cotton burrs. Cattle are then gradually adapted and transitioned to a more energy-dense, grain-based final finishing ration. This adaptation is generally accomplished over a period of ≥ 3 weeks, commonly either through a two-ration blending system or in a stepwise fashion.
Rations are often reformulated on a regular basis to account for changes in ingredient dry matter or to allow for the inclusion or exclusion of ingredients on the basis of price, with a common goal of minimizing the cost of weight gain. It is of utmost importance that any changes to the amount or composition of feed be made gradually, and that cattle be fed on a consistent schedule. Cattle are typically fed at least once daily, but often 2–3 times per day to increase feed efficiency.
The major feedstuffs used to finish cattle vary regionally and often depend on other major crops produced in the area. However, on a dry-matter basis a typical feedlot finishing ration may consist of ~65% corn grain; ~20% of a corn milling by-product such as wet distiller’s grains; ~10% roughage; and ~5% of "micro" ingredients, such as minerals, vitamins, fats, drugs, or other additives.
Conventional finishing rations often contain urea as a source of ruminally available nitrogen to satisfy a portion of the rumen degradable protein (RDP) requirement of rumen bacteria, and often consist of ~1.5%–3.5% added fat. Conventional finishing rations also typically contain an ionophore (eg, monensin, lasalocid, or laidlomycin propionate) and tylosin. Cattle are also typically fed a beta agonist such as ractopamine during the last month on feed. In addition, heifers may be fed a progestin. See Growth Promoters and Metabolic Modifiers for a brief discussion of these growth promoters and the important roles they play in finishing cattle.
Although feed blending and delivery strategies vary, most cattle finished in the US are fed a total mixed ration consisting of specific amounts of different ingredients blended homogeneously before being delivered to cattle. The major goal of this blending is to ensure that each bite of feed contains the animal's complete diet, to minimize sorting, and to ensure that animals eating from a different portion of the feed bunk or at a different time of day consume the same ration. Because of inherent differences in particle size and consistency, different ingredients should be sequenced and mixed for specific times to ensure that the blend is homogeneous. A mixer efficacy or total-mixed-ration consistency test can be used to objectively evaluate ration homogeneity.
Grains are typically steam-flaked or dry-rolled to increase digestibility and optimize starch availability. Steam flaking results in both physical and chemical changes to the structure of starch that increase its availability to the animal; it also increases the surface area of the grain to promote interaction with rumen microorganisms and digestive chemicals. As a result, steam flaking increases the amount of energy that can be liberated from the grain. Flake density, or bushel weight, is the major metric used to quantify the degree of processing for steam-flaked corn, and it is one of the factors closely monitored by consulting nutritionists.
Dry-rolling, or cracking, increases the digestibility of grain primarily by increasing its surface area, and it strikes an optimal balance in starch availability between feeding whole shelled and finely ground grain when steam flaking is not feasible or high-moisture corn is unavailable.
Although most US feedlots commonly rely on corn as the primary grain to finish cattle, economic conditions may warrant the replacement of corn with wheat, sorghum, or barley. Wheat should not be finely ground, because the rapid rate and extent of starch digestion substantially increase the risk of ruminal acidosis.
Depending on arrival weight, genetics, and targeted finished weight, cattle may be on feed for a period of 90 to > 365 days; most cattle spend 160–230 days on feed. Similar variation exists in dry matter intake and average daily gain; typically, however, cattle consume ~2.0%–2.3% of their body weight in dry matter when on full feed, and they gain ~3–4 pounds (1.36–1.81 kg) per head per day.
Ruminal acidosis and bloat are the two most common nutrition-related digestive disorders that affect finishing cattle. Cyclical dry matter intake patterns often result from bouts of ruminal acidosis due to overfeeding or inconsistent feed batching and delivery practices. An incidence of bloat in > 0.5%–1% of cattle should be investigated to determine whether a change in feeding management practices is warranted. For more detail about these disorders, see Ruminal Acidosis and Bloat.
Note that nearly all cattle that die from causes unrelated to bloat will bloat after they expire. Therefore caution should be exercised when using postmortem indicators of bloat as a cause of death, particularly if necropsy identifies other potential causes of death and the animal had not previously been observed to be bloated. Like bloat, ruminal pH begins to decline immediately after death of the animal. Therefore, postmortem ruminal pH should not be used as a major clinical finding to identify or support cause of death.
Grass- and forage-based finishing programs rely primarily on forages or other roughages as the main or sole source of nutrients. Therefore, they generally have a lower energy content than do cereal grains or their by-products. For this reason, more time is required to finish the animal.
Grass-based finishing programs should focus on agronomic and grazing management practices that extend the normal grazing season and promote the abundance of high-energy forages. Generally, cattle finished in grass-fed programs graze fresh pasture and forages throughout the growing season, and they may be fed hay or other harvested roughages during seasons, such as winter, when grazing resources are limited. In addition, depending on marketing strategies, some grass-fed cattle will be supplemented as necessary with other feedstuffs to achieve production goals. These supplemental feedstuffs are generally fibrous by-products that pair well with fibrous forages; however, they may also include grains.
Grass- or forage-based nutritional management programs for finishing cattle are typically less efficient than programs based on more energy-dense feedstuffs, such as cereal grains and their by-products. Because of this lower efficiency, the overall greenhouse gas emissions, expressed per unit of beef production, are greater from cattle finished on forage-based rations than from cattle finished on conventional grain-based rations.
