Can We Feed for Higher Milk Protein Content?

Abstract

The effects of feeding on the concentration and distribution of nitrogen in milk are considered. Increasing fermentable energy intake increases glucose supply to the mammary gland and, more importantly, increases ruminal microbial protein synthesis. The amount and balance of ruminally degradable/undegradable protein are important factors. Among protein sources, the quality of microbial protein is highest, with fish meal perhaps being the highest quality undegradable supplement. Dietary fat tends to decrease concentration of protein in milk but not protein yield; mechanisms by which fat influences protein content remain uncertain. Increasing knowledge of limiting amino acids for milk protein synthesis, together with new technology to protect amino acids from ruminal degradation, provide opportunity to refine feeding systems for increased milk protein content.In corn-based feeding systems, lysine is usually first limiting, with methionine second limiting. Adding methionine to lysine-limited diets often has a negative impact on milk protein percentage. Continuing development and increasing sophistication of computer-driven models for nutrient balancing allow opportunity not only to maximize milk protein content but also to decrease ration cost and nitrogen loss to the environment. A simple test for milk urea nitrogen may become a useful tool for properly balancing herd rations.