Dietary influence on protein level in milk and milk yield in dairy cows

Abstract

Diet can influence the yield of milk protein more than it can influence milk protein content. Providing sufficient dietary crude protein in forms that will maximize amounts of amino acids required for milk protein synthesis to the gastrointestinal tract, in forms that can be digested and absorbed, will provide for optimal milk protein yield and content. Maximizing ruminal microbial protein synthesis is an important part of this strategy. The rest of the strategy involves providing sufficient amounts of the remaining required amino acids as ruminally protected proteins, or amino acids in forms that can be digested in the gastrointestinal tract. A diet deficient in protein will reduce milk protein content 1 to 2 g kg −1 and may substantially reduce yields of milk and milk protein. A diet containing high amounts of readily fermentable carbohydrates may increase milk protein content 1 to 2 g kg −1, and may increase yields of milk and protein, but may also result in digestive and metabolic upsets. Diets containing supplemental fat will increase yield of milk protein, but not as extensively as the increase in yield of milk, because milk protein content is usually reduced 1 to 2 g kg −1. The increased efficiency of milk fat and lactose synthesis is likely to be the reason for this depression in milk protein content. A means of overcoming this problem is a continuing research challenge.