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September 2015
Evaluating dairy ration protein sources requires looking at multiple factors, especially in today’s ever-changing market. Research typically suggests using a very simple metric to evaluate protein in a ration: protein efficiency. This measures milk protein yield per cow per day as a function of protein consumed by eating the dairy ration. Currently, averages are between 25% and 30% – a value that has been steadily improving.
Protein serves two roles in a dairy ration:
Ingredients vary in the proportions of protein that go toward each function. Generally, the microbial protein needs are met with silages and other moist ingredients. However, a good portion of the protein in a cow’s diet should bypass the rumen to support her milk production; high-protein ingredients are added to the ration for this purpose.
In the past decade, better methods of assigning the distribution between “rumen available” and “cow available” (bypass) proteins have been developed. Ration analysis laboratories are rapidly adopting these, and feed formulators are ensuring that rations are balanced accordingly. An increasing number of dairy cow diets are being balanced for amino acids. By understanding what part of each feed protein reaches the intestine intact, it is much easier to match amino acid supply with amino acid need.
Protein efficiency has been steadily climbing, and some researchers have projected that it has the potential to reach 35%, or even as high as 40%. With a better understanding of how we should calculate rumen undegraded protein (RUP), effective feed analysis methods, and an improved ability to formulate diets on the basis of amino acids, ingredient selections can be made to reduce protein overages, and to reduce nitrogen lost to the environment.
Purchasing ingredients can be a challenging task, and, particularly in today’s ever-changing market, cost can be a major factor.
Commonly, proteins are purchased on the basis of their protein content. If one ingredient has 40% protein, and the other has 50% protein, should the lower-protein ingredient cost less than the high-protein ingredient? Not always. Part of the ingredient that is not protein is also providing valuable nutrients, including minerals, vitamins and energy. Additionally, the form of the protein is a key factor — considering whether the protein is high in rumen degraded protein (RDP) or RUP. If there is only 25% RUP in the high-protein ingredient, but 50% RUP in the low-protein ingredient, we are actually getting more RUP from the low-protein ingredient (0.5 times 40% = 20%) than from the high-protein ingredient (0.25 times 50% = 12.5%).
Systems that integrate RDP and RUP levels along with the contribution of other nutrients, such as the Dairy Feed Calculator, help to ensure that ration ingredient purchases more accurately reflect the value of the proteins that are available for feeding to dairy cows.
