Cattle require protein in large amounts to support core body functions and productivity1.
Cows in late gestation require protein to produce high-quality colostrum to nourish newborn calves. The protein requirement also supports fetal growth and development.
Protein requirements increase as the level of production increases. Protein requirements are influenced by feedstuff and forage quality as well as the size of the cattle.
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Protein Content of Forages
The protein content of a feedstuff varies considerably by plant species, soil nutrients, and forage growth stage. The protein content of forages is measured as crude protein (CP). Typically, cool-season forages contain higher crude protein concentrations than warm-season forages or hay. The CP concentration of forages decreases as the plants mature. This decline in protein concentration is a result of the buildup of plant cell walls that interfere with rumen microorganism digestion.
The rumen bacteria degrade the cellulose and other plant fibers to produce microbial protein and short-chain fatty acids. The microbial protein provides a source of nitrogen for the rumen cells to make amino acids. These amino acids are used as building blocks for proteins in other animals and for the growth and repair of the cow’s body tissues. In addition, rumen bacteria convert the fatty acid precursors to vitamin A in the form of retinol. The retinol is used for cell structure and the development of the immune and reproductive systems.
Protein is an essential nutrient for cattle and is required in all stages of life. During gestation, protein is needed for fetal formation and to produce immunoglobulins to help the calf fight disease. Protein is also important in a calf’s diet because it allows the calf to absorb vital nutrients from its mother’s milk.
Most beef cattle are able to meet their dietary requirements with high-quality grass, hay, or stored forages. However, there are some situations where the cows cannot get enough protein from the forage they consume. Protein supplementation is highly effective in increasing forage intake and digestibility during low-protein forage feeding periods.
Producers should evaluate the forage quality and protein concentration of their herds. If forage CP is less than eight percent, a protein supplement should be fed to stimulate forage intake and digestion.
Protein Content of Feedstuffs
Protein is essential to the health of cattle. The body uses it to build cells, transport nutrients and hormones, regulate the immune system, control metabolism, and other vital functions. It is also needed to break down forage and digest feedstuffs. Protein requirements are determined by an animal’s stage of production, frame size, and expected performance. For example, heavier cows need more crude protein per day than lighter ones but as a smaller percentage of total dry matter intake.
Many forages and feedstuffs provide high levels of ruminally degradable protein. These proteins are absorbed across the rumen wall and converted to microbial protein. However, a portion of this microbial protein is not metabolized by the animal and is referred to as escape protein.
The ability of forages and feedstuffs to provide a sufficient amount of ruminally degradable protein is limited during the winter when grazing pastures decline in quality. During this time, most producers will add small grains or high-protein byproducts to the diet of lactating cows and first-calf heifers to meet their energy and protein requirements.
In addition to supplying protein, these supplemental feedstuffs typically provide substantial energy. For this reason, when comparing different forages and byproducts, it is important to evaluate their energy content on a dry matter basis rather than on a percent protein or nitrogen basis.
For example, a well-conditioned 1,100-pound cow consuming low-quality forage with a crude protein content of 5.5% requires approximately 0.45 pounds of supplemental ruminally degradable protein. A supplement containing 40% cottonseed meal provides the necessary amount of ruminally degradable crude protein to this cow.
A similar calculation can be used to determine the number of pounds of rumen undegradable protein required in the diet of a mature steer being fattened for beef. A typical corn-based concentrate fed to such cattle will contain approximately 15 to 20 percent of rumen undegradable protein on a dry matter basis. A mature steer needs about 0.8 pounds of this protein during one fill-up grazing bout in the rumen. This is the equivalent of about 4 pounds of a 20% protein supplement.
Protein Content of Supplements
The protein content of feedstuffs and supplements can significantly affect how well beef cattle perform. While energy requirements usually receive the greatest emphasis when making nutrient supplementation decisions, beef cows need adequate levels of specific proteins to maintain milk production and perform after calving.
Protein needs increase with a cow’s stage of production and the rate of milk production she produces. For example, a mature cow producing 2 lb. of milk per day requires 1.6 lb. of crude protein per day. In addition, the protein requirement of pregnant and lactating cows is increased significantly over maintenance requirements due to protein synthesis associated with lean tissue mobilization and the production of high-quality colostrum that provides newborn calves with their primary immune system.
The ability of a forage to meet a cow’s protein requirement depends on its protein concentration and its rumen degradability. For example, a forage that contains 11% crude protein may only be ruminally degradable to about 40% of its nitrogen content (microbial crude protein). When the forage has such a low rumen degradability, it must be supplemented with a higher quality protein source such as cotton seed meal or soybean hulls to meet the cow’s protein needs.
During the winter, when most native warm-season forage has reduced protein concentrations to less than 8% crude protein, many producers supplement with protein-based products, such as a 38% protein range cube product or a 20% cottonseed meal supplement. These products can be used in combination with a high energy or total digestible nutrients (TDN) supplement, such as corn grain, wheat middlings, or milo, to provide the proper protein concentration to match the cow’s nutritional needs.
It is important to determine a cow’s protein requirements and evaluate the available supply of forage, hay, or stored forages and potential supplement alternatives on a cost-per-unit-of-nutrient basis. In most cases, a supplemental protein source is only needed when a cow cannot meet her requirements with the forage and feeding rates she can consume. When this is the case, a more expensive alternative should be evaluated regarding its ruminally degradable protein content and overall cost.
Protein Content of Calves
Protein plays an important role in many aspects of beef cattle alfalfa nutrition. It provides ruminal bacteria with a source of nitrogen, which they use to make their own proteins, and it is an important component in the diets of growing cattle, which require high levels of crude protein and nutrients for maximum performance. Protein is also an essential nutrient for lactating cows. It provides a rich source of immunoglobulins, which protect the newborn calves from diseases.
In general, ruminants need to consume between 7 and 8 percent crude protein in the diet for proper function. If the protein content of the forage is lower, the cows may become deficient in this nutrient and experience poor health or reduced milk production.
Forages in the Western United States typically do not contain enough crude protein to meet the daily requirements of most beef herds. This necessitates a seasonal supplementation program to ensure that herds have the nutrients necessary for optimal performance. The supplements needed for this purpose must be high quality and cost-effective to minimize the risk of protein deficiency in herds.
When determining the protein content of feedstuffs, it is most common to express the nutrient concentration in terms of the percentage of the feed’s total dry matter (DM) content. The CP content of the feedstuffs can then be divided into ruminally undegradable protein (RUP), ruminally degradable protein (RDP), and, to a lesser degree, endogenous CP.
The dietary protein requirement of cattle depends on the stage of life, size of the animal, and expected performance. For example, young, growing cattle need more pounds of CP per day than mature, pregnant cattle but as a smaller percentage of their DM intake.
In early gestation, a pregnant cow’s protein needs are similar to those of a maintenance animal. However, her requirements increase dramatically during the later stages of gestation, primarily due to the growth of the fetus. Mary Drewnoski, Nebraska Livestock Systems Specialist, notes that this is a critical time to supply adequate levels of protein because the mother’s protein level must be sufficient to produce sufficient quantities of high-quality colostrum, which provides her calf with an immune system.
