The Amino Acid Content of Rumen Microbes, Feed, Milk and Tissue after Multiple Hydrolysis Times and Implications for the CNCPS

Abstract

The amino acid (AA) profile and content of the feeds and microbes in the supply side of the Cornell Net Carbohydrate and Protein System, along with the requirements for milk and tissue are important as we move away from crude protein and metabolizable protein and start to balance diets on an AA basis. During the reconstruction of the CNCPS (Higgs, 2014) into version 7, the model was developed on a nitrogen (N) basis and each AA was described as a function of its N content, thus eliminating any numerator and denominator in the calculations of content or flow. Although total non-ammonia N flow was predicted with high precision and accuracy, there was a bias in the prediction of several AA that could not be explained by any conditions we were aware of. Thus, a series of studies were conducted to understand the source of the bias. The AA profile and content of feeds and microbes was re-described using both a standard hydrolysis of 21 hr and a long-term hydrolysis method, 168 hr, as described by Darragh and Moughan (2005), Rutherfurd (2009). The long-term hydrolysis resulted in greater recoveries of certain AA and destruction of others however, when the two methods were used together, the outcome was greater AA recoveries and an improvement in the bias of AA predictions in the CNCPS v7. This will be described in detail and context in the manuscript and talk.