The American Dairy Science Association recently held a Discover Conference in Itasca, Illinois, to review the present understanding of amino acid requirements for dairy cattle and consider the future opportunities for further research and application of knowledge in this area.
Progressive Dairyman reached out to several nutritionists who were in attendance for their thoughts and comments about what was discussed.
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Technical Services and Research Director
RP Feed Components
Nutritional and Management Consultant
Reveille Livestock Concepts
Technical Advisory Services Inc.
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Fox Hollow Consulting
What was the maintake-home message for youfrom the conference?
That the cow’s nitrogen utilization efficiency can be improved if the diets are formulated correctly. Practicing nutritionists need to start thinking, not about the amino acid profile of the diet’s ingredients, but rather about the amino acid profile the cow has at her disposal to use to meet her requirements.
The amino acid status of all rations should be evaluated because cows require amino acids, not crude protein or metabolizable protein. Although we are not ready to abandon the metabolizable protein system, research should continue to focus on refining amino acid requirements so in the future we can formulate for each of the 10 essential amino acids.
Protein nutrition in ruminants remains incredibly complex. We take steps daily to improve our understanding of amino acid nutrition and requirements in the dairy cow, but given the complexities of the rumen, the variation in requirements as related to stages of production and the inherent variability of the typical dairy cow diet, having a truly accurate picture of what the requirements are and how to meet these remains elusive.
The dairy industry now averages about 30 percent efficiency of N use (milk output/intake), which is lower than swine and poultry. We can likely increase this to 40 percent with the current technology we have at hand.
We have made a lot of progress in the 10 years since the last Discover Conference on amino acid nutrition, both in research to understand the basics of amino acid supply and utilization in ruminants, and in applying the knowledge gained to ration balancing for “real-world” dairy cattle feeding.
A lot of progress was made over the last 10 years in understanding how dietary, ruminal, microbial and physiological factors affect amino acid supply and utilization in the dairy cow. The future looks bright in regards to revising models to more accurately and consistently predict cow response to amino acid balancing.
In your opinion, what is the next realistic step to improving how amino acid requirements and feeding are applied in nutrition programs for commercial dairies?
Models keep evolving, and ease of use is key to apply least-cost amino acid balancing. Producers and practicing nutritionists need to look at amino acids as required nutrients that improve not only milk protein production but also affect the cow’s metabolism and improve the diet’s nitrogen utilization.
Use a nutritional model that incorporates the latest research on amino acid supply and requirements. Then formulate rations using model-specific guidelines with adjustments based on user experience and cow responses. Set expectations, which may not always be increases in milk flow and component yield. Additional benefits of amino acids include the interactions with health and reproduction.
As an industry, we need a standardized assay for the analysis of the digestibility of rumen-protected amino acids in the animal. Only then can we truly determine which products and methods of protection are efficacious and cost-effective in the cow’s diet. Again, biological variability creates challenges that make this process difficult, but having a standard of comparison can make the nutritionist’s job at least slightly easier.
Better lab analyses. The techniques we are using are currently out of date. Labs measure soluble protein but give no indication of the rate of degradation of the soluble protein. Some labs provide protein pools but no rate values.We as an industry do not routinely analyze protein ingredients and grains to the extent that we measure forages. We assume that file values are good enough. Fortunately, our forage testing labs are eager to do a great job for the industry and are just waiting for more input from the scientific community.
What one thought did you have during the conference that had never occurred to you before?
The role of amino acids goes beyond simply being the building blocks of proteins. They also have a cellular signaling function, acting like hormones, to influence the balance between protein synthesis and degradation.
We should dismiss the single-limiting nutrient (i.e., single-limiting amino acid) response model and move to a multi-limiting nutrient model. Existing data indicate that when two nutrients are limiting, such as methionine and lysine, a response to either nutrient can be expected, and the response to both will be additive.
That amino acid nutrition can have the level of effects that have been observed on the reproductive performance of the cow (i.e., increasing arginine levels have been shown to enhance blood flow to the uterus). This presents the question: What other effects on various physiological functions might the other essential amino acids have that we haven’t discovered yet?
We really need to better understand the nutrient needs and usage by the gut. We can predict the nutrient supply entering the gut, but not what appears in the supply that is available to tissues beyond the gut.
That MUNY/PY (milk urea nitrogen yield/protein yield) proposed by Dr. Michel Wattiaux of the University of Wisconsin – Madison may be a better measure of N efficiency in dairy cattle because it focuses on the post-absorptive use of amino acids and N recycling for maintenance and milk protein synthesis rather than protein digestibility. Protein digestibility of cattle feed ingredients is less than those used in monogastric rations due to the nature of the ingredients; why should we penalize ruminants for being able to utilize feeds that are inedible/undigestible to other species?
Dairy nutritionists need to think like swine nutritionists. I learned that to improve prediction of amino acid supply relative to requirements, individual amino acids should be expressed relative to metabolizable energy instead of metabolizable protein. This is the approach used with monogastric animals and CNCPS version 7. PD