Feeds, Prediction of Energy and Proteins | Feed Proteins

Abstract

Most milk-producing animals are ruminants which are the only mammals with the unique ability to survive, grow, reproduce and lactate without a dietary source of true protein. Forestomach fermentation of feedstuffs supplies substrates for synthesis of microbial protein. The amino acid profile of microbial protein is very similar to that of milk protein. In addition to microbial protein, ruminants utilize amino acids and peptides from the dietary protein that escapes rumen degradation. Based upon intrinsic characteristics of the protein source, as well as animal factors such as dry matter intake, proteins can either be degraded within the forestomachs or remain intact and escape rumen degradation. Research conducted in the 1960s demonstrated that lactating cows were able to produce up to 4500 kg of milk per lactation when fed diets containing no true protein. However, ruminal microbes do not provide enough protein for maximum milk production in most contemporary dairy animals. Dairy cows are not efficient animals in converting dietary N into milk protein. Because extensive degradation of proteins within the rumen can increase N wastage and decrease efficiency of N utilization, strategies to formulate diets with protein sources that are more resistant to microbial degradation have been proposed. A balance between optimum microbial protein synthesis and supply of ruminally undegraded protein (RUP) with a balanced amino acid profile and of high intestinal digestibility is important.