Estimation of the supply of metabolizable protein in dairy cattle

Abstract

Protein is an essential nutrient in the diet of dairy cows as it provides amino acids for the animal and, at the same time, supplies nitrogen for the rumen microorganisms; therefore, part of the protein available to ruminants comes from microbial protein and dietary sources. In most feeding situations, microbial protein is the primary source of absorbed AA; however, when large amounts of rumen undegradable protein are fed to the animals, microbial protein may not be the primary source. Metabolizable protein is the true protein absorbed as amino acids by the intestine and supplied by microbial protein, endogenous protein and dietary protein that escapes degradation in the rumen. Normally, the concept of crude protein is used; however, this can incur in excess protein that, in addition to being expensive, can cause problems to the animal and the environment, thus the objective of this document is to present an extract of the methodology used by the NRC (2001) model to determine metabolizable protein requirements in dairy cattle. Within the steps, it is required to calculate the maintenance requirement that includes urinary endogenous nitrogen (N), scurf N, fecal metabolic N and endogenous N, and the requirement for milk production. To determine the metabolizable protein contribution of the ration, it is necessary to calculate the amount of total digestible nutrients (TDN) supplied in the ration. Despite the fact that many years have passed since the publication of the nutrient requirements of dairy cattle, and that there are computer programs that perform these calculations, it is intended to detail the way in which the calculations are carried out to make this information more accessible to potential users in Costa Rica and Latin America.