As we work to understand the nutrition, physiology and genetic potential of the beef animal, we grow closer to formulating and implementing more precise feeding and supplementation programs. Ongoing research, model development, ingredient analysis, improved skill in feeding management, etc., lead us to better understand the complexities of the rumen and the animal itself. The ultimate goal is the development of nutrition programs that best and most cost-effectively support reproduction, growth and health of the cow, as well as growing and finishing cattle.

Blezinger stephen
Nutritionist / Reveille Livestock Concepts
Dr. Stephen Blezinger is a nutritional and management consultant with an office in New Ulm, Texas.

A primary component of the nutrition of the beef animal is protein. For years, our focus has been on crude protein supplementation of cow herds on various forages or feeding programs, since many forage systems as well as feed ingredients do not provide adequate protein to support requirements. We commonly look at various protein supplements to meet these needs as cheaply as possible. Perhaps one of the most common questions asked at the local feed store is, “What 20 percent protein-range cubes do you carry?”

Protein basics

Our understanding of protein nutrition has improved, and we know that much of the protein the ruminant animal digests and utilizes is that of microbial protein, protein that is synthesized through normal rumen fermentation by the microbial population. When the cow, growing calf or feedlot steer consumes whatever diet it is on, (pasture, hay, supplements, growing/finishing rations) these feed and forage materials are broken down in the rumen to core components – in many cases to the basic nutrient or even molecular composition. These are then ingested by the microbes and resynthesized as proteins and other nutritional molecules. The microbes (mostly bacteria) pass from the rumen into the other rumen system compartments and on into the small intestine, where they are digested and absorbed by the animal. So to a very large degree, the protein the cow or calf receives is this microbial protein.

Amino acid basics

One thing we know about all proteins is that they are composed of smaller molecules known as amino acids. These include lysine, methionine, histidine, cystine and glycine. There are a total of 20 amino acids, nine of which are considered essential (required by the animal and must be received through dietary sources). The other 11 are considered nonessential and can be synthesized in the body. All proteins have an amino acid profile, meaning that each specific protein is made up of a specific group of amino acids bound together in a specific structure.

What we have learned over years of research is that microbial protein, which makes up the majority of the protein in the animal’s diet, also has a specific amino acid profile. It may vary based on the actual diet the animal consumes, but microbial synthesis of protein in the rumen is a pretty standard process, which means there is not a huge amount of variability. However, it is known that cattle on a high-grain diet (i.e., finishing diets high in corn) are typically short in one of the most well-studied amino acids: lysine. Corn is known to be low in lysine compared to other grains or forages. Some studies have shown that supplementing the lysine levels in these high-grain diets can improve average daily gains (ADG), feed efficiencies and final end weights in finishing steers. Additionally, cows on forage-based diets (pastures, hays, silages) are also generally deficient in lysine as well as methionine.


The majority of work on amino acid feeding and supplementation to cattle has been by the dairy industry. It is now well known that proper supplementation of these critical amino acids improves milk volume, components such as butterfat and milk protein, and the overall well-being of the animal. It has been shown repeatedly that the overall amount of crude protein supplementation can be reduced by properly supplementing lysine and methionine in the diet.

Similar work (though not as extensive) has been done on beef cattle. While positive results have not been as well recognized as in dairy cows, some advantages have been noted by supplementing amino acids to both cattle on pasture and on finishing rations. In growing and finishing cattle, supplementing lysine, particularly in diets higher in corn, has been shown to improve overall gains and feed efficiency, even at low feeding rates. Use in breeding cows has also been studied, but the results have not been as clear-cut, largely due to the typical intake variations in grazing cattle as well as changes in forage quality.

Forms of fed amino acids

In the dairy industry, use of rumen-protected amino acids (RPAA, primarily methionine and lysine) has become fairly standard. In recent years, numerous products have emerged showing effectiveness as supplements for either lysine or methionine in the cow’s diet. Unprotected amino acids are commonly used in monogastric feeding (pigs and chickens) and are digested well. Feeding an unprotected source to cattle allows these amino acids to be broken down in the rumen by the microbial populations so little or no advantage is realized. Some studies have even shown that feeding an unprotected amino acid source may actually depress intake in growing or finishing cattle.

Numerous sources of protected lysine and methionine have been developed over recent years and have been fed in the dairy industry regularly. These amino acids are protected either by the application of a “coating” (a polymer in some cases, fats in others – think of a peanut M&M) or inclusion in a fat matrix (think Nestle Crunch pieces). In some cases, amino acids complexed with certain trace minerals have also been used as a source of RPAAs, though this is not cost-effective.

Whatever the case, the coating or combination prevents rumen microbes from breaking down the amino acid while in the rumen.

This protection from rumen effects has proven beneficial to improving the digestion and absorption of these amino acids directly by the animal and thus improves animal performance. A 2022 study at Kansas State University showed improvements in the performance of both growing and finishing cattle supplemented with rumen-protected lysine (RPL). Steers fed 6 grams per head per day in the growing phase performed best during the finishing phase. During finishing, steers fed 3 grams per head per day showed the best ADGs and feed efficiency, as well as the greatest carcass weights.

Another study evaluated feeding of RPL and rumen-protected arginine to finishing cattle and found improvements in longissimus muscle (LM) area, decreased fat thickness and yield grade, and increased moisture content of LM steaks. So effects on muscle tissue development and fat deposition have likewise been noted.

Use of RPAAs may also find greater application as we evaluate in combination with the various implant strategies and what can have the greatest effect on gain efficiency and carcass performance.

As mentioned earlier, a great deal of use of RPAA is found in feeding dairy cattle, especially when milk and component production are considered. As the beef industry focuses more on milk and components and the need to increase these to support calf growth and weaning weights, it will potentially find an opportunity with RPAA supplementation. There is simply a need to expand research in these areas, as well as potential effects on reproduction and health.

Finally, there’s always that final detail of cost. While we always seek that supplement that appears to be the most cost-effective, we are reminded that “least cost” is not always “best cost.” As we continue to evaluate the use of these products in beef cattle diets and supplements, cost-effectiveness is always the bottom line. At this point, this requires more evaluation as well.

References omitted but are available upon request by sending an email to the editor.