by: Stephen B. Blezinger
Ph.D., PAS

One of the most common topics discussed when feeding pasture and breeding cattle is protein. Producers are concerned with crude protein in their hays, pastures, supplements and so on. We regularly concern ourselves with 20 percent protein range cubes, 35 percent protein liquid feeds or 24 percent protein tub supplements. Crude protein (CP) is a number we regularly use to compare hays or supplements and to assign value to whatever it is that we might be feeding. Producers tend to be concerned about crude protein over almost any other nutrient. But research and practice have shown us there is a great deal more to providing for the crude protein needs of the animal. We now know that other forms of measurement have been identified that are of use in measuring and meeting these requirements. Terms such as soluble, degradable and un-degradable protein have all broadened our understanding of how protein from various sources are degraded and utilized in the rumen. Current ruminant nutrition, particularly in dairy animals have taken these steps farther, looking at how these proteins and their component parts, amino acids behave and are utilized by the rumen bacteria as well as the cow itself. This article is focused on amino acids in the cow's diet and what we know and don't know about this area of study. Over the last 20 + years, numerous universities, research foundations, company and farm trials have researched and attempted to illustrate the value of amino acid balancing and supplementation for beef breeding cows, as well as growing and finishing cattle.

Let's Review a Little

You might remember from high school biology that proteins are larger molecules made up of smaller molecules known as amino acids. Proteins are used for a wide variety of applications in the cow including muscle tissue synthesis, milk production, components of the immune system, countless enzymes in the body and so on. Proteins are literally the building blocks of the cow or calf.

When the cow consumes a protein source be it grass or hay or feeds or supplements they are consuming proteins. These proteins will be in various forms and will be incorporated into with fiber components that have a direct effect on the protein digestibility by the animal. Grain sources have other protein configurations and these proteins can be incorporated with fibers or carbohydrates. This is a bit of a misunderstanding many folks have. When we talk about proteins, fats, fibers, carbohydrates, etc. we tend to think of them as all stand-alone molecules. They are not. They are intertwined and bound with one another creating a complex combination of nutrients the rumen microbes use initially and the cow uses “down the road.”

A point here is that under typical circumstances the cow consumes the forages and feeds that it does and once in the rumen, the microbes break these down into much smaller particles. The proteins are broken into amino acids and the amino acids down into ammonia (nitrogen source) and small very short carbon chains. Then other bacteria take up this nitrogen source, combine it with other carbon and form bacterial proteins. This bacterial protein is the primary source of protein from the animal. While, in general, this is an adequate protein for the cow to live and perform on, in many cases the bacterial protein does not include the optimal combination of amino acids for the animal. Research has shown that for cattle on pasture, of the 20 amino acids that make up proteins, the amino acid Lysine (Lys) is generally the first limiting amino acid. This means that under typical grazing circumstances the cow will run short of Lys in its diet relative to what it needs to produce milk or other protein “products.” Through work done largely by the dairy industry we know that supplementing pasture cattle with Lys the animal's milk production and milk quality can be improved. Similarly, researchers have found that cattle on high grain diets will find Methionine to be the first limiting amino acid. By supplementing with Met, gain performance has likewise improved in growing and finishing cattle. Growth performance when amino acids were properly balanced, meaning that all requirements were met, resulted in gains improved by about 10 percent with a 9 percent improvement in feed efficiency.

Supplying Lys or Met to cattle can be accomplished a variety of ways. Various high protein meals (from plants) contain moderate to good levels of Lys and Met (Soybean meal, Corn gluten meal, etc.). The problem the producer and nutritionist face is that typical sources of lysine or methionine are extensively degraded in the rumen and even when higher levels of these amino acids are fed, they can still be readily broken down by the rumen bacteria. Animal protein sources such as fish meal, blood meal (pork or poultry), feather meal, poultry meal are commonly quite high in Lys and Met and can act as good sources to the beef animal. Like anything there are no perfect circumstances. Animal proteins tend to be expensive and a variety of issues make use more difficult. Finally, public perception of the use of these products has created pressure against various livestock and poultry industries to minimize their use.

Over recent years production of purified sources of both Lys and Met has become common. Like conventional plant based protein sources, the average Lys and Met, are readily broken down by ruminants. A version of these amino acids referred to as “rumen protected” amino acids have been developed which have a coating of some type on the outside of the molecule that prevents it from degradation in the rumen.

Responses to supplementation with lysine or methionine (where both are protected in some manner from ruminal activity) have been extensive and well documented. The most basic and commonly accepted benefit in dairy cattle is thought to be in terms of improvements in milk volume and milk components (milk fat and protein). Other documented benefits include improvements in reproduction, embryo survivability, offset of oxidative stress during transition periods (the period before, during and after calving) and potentially reducing heat stress effects. Economically, opportunities have been observed to reduce overall crude protein levels in the cow's diet during lactation when amino acids are balanced. Thus provides for an opportunity to reduce feed cost and improve profits. In general, it is well-proven that balancing the amino acid component of the typical dairy cow diet can bring very positive results. Similar results have been shown when Lysine and Methionine have been supplemented to beef cattle.

As noted above, however, the answers are not always simple. A factor that complicates the matter has been a question of sources. Over history, basic feed ingredients such as blood meal, fishmeal, soybean meal (conventional and heat or other process) have provided, to at least some degree, a supplemental level of lysine and methionine to meet the animal's needs. Obviously some sources are more effective than others in terms of concentrations or ability to by-pass the rumen and provide direct absorption in the small intestine. Another consideration is that many of these materials are actually by-products which commonly vary in their nutrient concentrations. Finally, with the use of these ingredients as an AA source, comes the issue of cost/market variation, which in some cases can be quite extensive.

With the advent of “synthetic” or manufactured amino acid sources addressing the need for a specific amino acid is somewhat simplified. With this, the addition of technologies to protect the specific amino acid from the microbial activity of the rumen has improved our ability to deliver a larger amount, unaffected, to the small intestine for absorption. Although some nutritionists question the performance of these products relative to “natural” or conventional feed ingredient sources, a large volume of research illustrates repeatedly that the animal does respond to feeding of men protected amino acids.

As with most other nutritional supplements, there are numerous products sold under the description of rumen protected amino acids (RPAA). Additionally, as with other nutrient sources, RPAAs vary in the actually technology used in the manufacturing process. In this case the variation is found in how each product provides rumen protection. In general, this protection is provided by the AA in question being combined, through very specific processes, with compounds that are resistant to microbial effects in the rumen. These technologies include polymer coatings, fat coatings, fat matrixes and so on with each product and the producing company having a proprietary process in place for production. The various coatings and compositions affect how well the AAs avoid ruminal breakdown as well as how the AAs are released in the small intestine for absorption. The correct combination of components that results in a precise response in the rumen and then the intestine can be difficult to achieve. The products that are believed to work the best are those that can deliver the AA of choice through the rumen with as little loss as possible but then release the AA in the small intestine so the greatest amount possible may be absorbed into the blood stream. This process needs to be done for the best possible cost. Finally, the true measuring stick is how the cow actually performs when the AA in question is supplemented in this manner.


Balancing of amino acids, particularly Lys and Met have shown promise in improving beef cattle performance both on grass and in confinement. Additionally data taken from dairy research is also showing that we may be able to reduce the level of protein fed when amino acids are balanced to meet the animal's requirements. This can obviously help in reducing feed costs. Your nutritionist can provide additional information on how to best utilize supplemental amino acids in your feeding programs.

Copyright – Stephen B. Blezinger, Ph.D., PAS – February 2017. Dr. Steve Blezinger is and nutritional and management consultant with an office in Sulphur Springs Texas. He can be reached at (903) 352-3475 or by e-mail at For more information visit us on Facebook at Reveille Livestock Concepts.

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