Nutritional manipulation of milk protein concentration and its impact on the dairy industry

Abstract

Milk protein accounts for about 25 percent of total milk solids and is now a more valuable component of milk than fat. This paper is a short review of some of the dietary factors that can affect milk protein concentration and yield. Milk protein consists of a number of different components, the greatest of which is casein. This in the most important component for cheese and casein powder manufacture but, generally, nutritional manipulations do not significantly change the relative proportions of the different protein components. Increasing amino acid supply to the mammary gland is the basis for most dietary manipulations to increase milk protein concentration or yield. Protein level in the diet does not affect milk protein concentration. However the type of protein fed can have an effect and including fishmeal generally increases milk protein concentration and yield. Feeding higher levels of concentrate supplement, thereby increasing the plane of nutrition of the cow, increases both milk protein concentration and yield. While in theory it would be expected that feeding starchy ingredients would increase milk protein, this has not been shown clearly in experiments. The inclusion of high oil levels in the concentrate supplement tends to reduce milk protein concentration. Infusion of casein or essential amino acids post-ruminally increases milk protein concentration but the response to feeding rumen-protected lysine and methionine has been variable. Cows grazing clover swards have higher milk protein concentration and yield than those grazing perennial ryegrass swards. It is important for the farmer to try and increase milk protein concentration and yield using both nutritional and breeding strategies. It is likely that in the future milk protein will continue to become more valuable relative to the other components of milk as protein concentration is of great importance to the milk processor in the manufacture of a range of products.