Improving protein nutrition in cattle with amino acids

Published on: 10/9/2018
Author/s : Steve Blezinger / Nutritional and Management Consultant.
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 is a number we regularly use to compare hays or supplements and to assign value to whatever it is 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 other forms of measurement have been identified that are of use in measuring and meeting these requirements. Terms such as soluble, degradable and undegradable 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 further, looking at how these proteins and their component parts (amino acids or AAs), behave and are utilized by the rumen bacteria as well as the cow itself. Let’s focus on AAs in the cow’s diet and what we know and don’t know about this area of study.

Let’s review a little

You might remember from high school biology: Proteins are larger molecules made up of smaller molecules known as AAs. 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 many others. Proteins and AAs are literally the building blocks of the cow or calf.
When the cow consumes a protein source, whether it’s grass, hay, feeds or supplements, they are consuming proteins. These proteins will be in various forms and will be incorporated within 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.
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.”
The point here is: Under typical circumstances, the cow consumes the forages and feeds and, once in the rumen, the microbes break these down into much smaller particles. The proteins are broken into AAs and the AAs down into ammonia (nitrogen source) and short carbon chains.
Then other bacteria populations take up the nitrogen source, combine it with carbon chains and form bacterial protein. This bacterial protein is the primary source of protein for the animal. While 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 AAs for best animal performance.

First limiting AAs

Research has shown for cattle on pasture, of the 20 AAs that make up proteins, lysine (Lys) is generally the first limiting AA. This means under typical grazing circumstances, the cow will run short of Lys in its diet relative to what it needs to produce milk, gain weight, rebreed, etc. Through work done largely by the dairy industry, we know when pasture cattle are supplemented with Lys, milk production and milk quality can be improved.
Similarly, researchers have found cattle on high-grain diets will find methionine (Met) to be the first limiting AA. By supplementing diets with Met, gain performance has likewise improved in growing and finishing cattle. When AAs were properly balanced, meaning Lys and Met requirements were met, 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 for the producer and nutritionist is: Typical sources of Lys or Met are extensively broken down in the rumen and, even when higher levels of these amino acids are fed, they can still be readily broken apart by rumen bacteria.
Animal protein sources such as fish meal, blood meal (pork or poultry), feather meal and poultry meal are quite high in Lys and Met and can act as good sources to the beef animal. But 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, common Lys and Met are readily broken down by the rumen. Sources of these AAs, referred to as “rumen-protected” AAs, have been developed that have a coating of some type on the outside of the molecule that prevents it from degradation in the rumen.

Supplemental AA response

Responses to supplementation with rumen-protected Lys or Met have been extensive and well documented, particularly in dairy cattle. 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.
Balanced use of rumen-protected Lys or Met has been observed to reduce overall crude protein requirements in the cow’s diet. This provides for an opportunity to reduce feed cost and improve profitability. In general, it is well proven balancing the AA component of the typical dairy cow diet can bring very positive results. Similar results have been shown when Lys and Met have been supplemented to beef cattle.
As noted above, the answers are not always simple. A factor that complicates the matter has been a question of sources. Historically, feed ingredients such as blood meal, fishmeal, soybean meal (conventional or heat-treated) have provided a supplemental level of Lys and Met to meet the animals’ needs.
Certain sources are more effective than others based on concentrations or ability to bypass the rumen and provide direct absorption in the small intestine. Another consideration is: Many of these materials are actually byproducts, which commonly vary, in their nutrient concentrations.
With the advent of “synthetic” or manufactured AA sources, addressing the need for a specific AA is somewhat simplified. With this, the addition of technologies to protect the specific AA from the microbial activity of the rumen has improved the 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 the cow or calf does respond to feeding of rumen-protected AAs.
As with most other nutritional supplements, there are numerous products sold under the description of rumen-protected AAs. These products vary in the technology used in the manufacturing process. In this case, the variation is found in how each product provides rumen protection.
The rumen-protected AA sources believed to work 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 bloodstream. 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 AAs, particularly Lys and Met, have shown promise in improving beef cattle performance both on grass and in confinement. Data taken from dairy research is also showing we may be able to reduce the level of protein fed when AAs 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.
This article was originally published on and is reproduced with permission from the author.
Author/s :
Consultant for ICC Brazil
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