Lysine use in Dairy Cattle

By Kraig Peel, Ph.D

     Everyone knows that all animals require nutrients in order to sustain life. When we start asking animals to produce a product as well as stay alive, we have to be very aware of the nutritional changes for that animal. Milk production is a metabolic demand on dairy cows that is unique and very nutritionally challenging. If all of her nutritional demands are not met through the diet, then the animal has no choice except to limit production. Most of our dairy animals depend on the dairyman to provide for all of her nutritional needs. Nutritionists work for and with dairymen to provide all of the nutrients a cow needs on a daily basis in order to stay alive, produce milk and rebreed. If there are nutrients that are limited, the cow will not be able to perform at the level we expect. 

      Protein is one of the nutrients that can have a significant impact both positive and negative on dairy production. We must be aware of all of the inputs of the ration and how they contribute to satisfy the overall needs of the animal. Overall protein can be measured in the ration, but we can also further reduce protein down to individual amino acids.  All protein is composed of differing specific amino acids. The monogastric nutritionists have long known that limiting certain amino acids to animals can have a significant impact on performance. Ruminant nutritionists have more recently become aware that the same dynamic of rate limiting amino acids can be realized by ruminant animals.

        Lysine is one amino acid that has been identified as being a rate limiting step in dairy cows. Not only does a lysine deficiency reduce the amount of milk a cow will produce but has also been shown to effect milk protein. Lysine can also be more complex. There is a relationship between metabolizable protein in the diet and methionine. It is important to balance lysine and methionine for optimal milk production and milk components.

        Lysine can be found in some of the feed products that are common in dairy cow diets. Most high protein components will contain significant amounts of lysine. Commodities like soybean meal, blood meal and some specialty forages will provide lysine toward the animal’s requirement. Ruminants present a unique challenge that is not realized in monogastric animals.  The rumen microbes get to take the first shot at the protein that we provide in the ration. The microbes may cleave some of the longer chain proteins into smaller chain proteins that have the potential to be further degraded so that the quality of the protein is much less by the time it gets to the small intestine. The small intestine is the primary site of nutrient absorption in all animals.

        We have to keep microbial degradation in mind when thinking about proteins and meeting the animal’s requirement when formulating rations. When a nutritionist works to supply the correct protein via amino acids, it is called amino acid balancing. The nutritionist is not only balancing the protein for the animal but further breaking down the animal requirements for protein into individual amino acids. This process is extremely important to ensure that even the smallest needs of the animal are met in adequate amounts. Most nutritionists utilize a computer program that we refer to as a model. It is called a model because the biology of the animal and the composition of the ingredients in the ration are utilized to estimate or predict how the commodities that we are feeding contribute to the overall needs of the animal. The better models help us to predict the level of degradation by the rumen microbes and to estimate the amount of an amino acid that actually reaches the small intestine available for absorption and subsequent utilization by the animal. If the model indicates that the commodities are not able to meet the needs for an amino acid like lysine, then we have to supplement lysine into the ration through another source.

        There are currently a multitude of supplemental lysine sources that are readily available.  The key to keep in mind is that all lysine supplements are not created equal.  We have to consider bioavailability of lysine. Bioavailability is the percent of a substance that is absorbed.  A higher bioavailability means that a nutritionist can feed less and still meet the needs of the cow.  Many lysine sources degrade in the rumen and do not reach the small intestine for absorption in large amounts. There are many companies that are producing ruminally protected lysine sources. These products escape microbial degradation in the rumen and reach the small intestine in higher quantities. These products will have greater bioavailability and therefore better bang for the buck.

        All nutrients are required by the animal and all can limit production.  Lysine is one amino acid that has been shown through multiple research trials to be a rate limiting step in dairy production if it is not available in adequate amounts for the animal.  Amino acid balancing and providing adequate quantities of lysine for absorption will enable the cow to reach her genetic potential for milk production. If your cows are reaching their genetic potential, there will always be a positive effect on the bottom line.