Abstract

Conversion of feed protein into milk protein is a basis of sustainable dairy production systems from both economic and environmental perspectives. This project addresses the need for rapid screening tools to support nutritional and breeding strategies to improve the efficiency of converting feed into milk protein. The approach is based on the phenomenon of N isotopic fractionation, whereby N sinks become relatively enriched or depleted in 15N, as a result of differential incorporation during various biochemical reactions. Macko et al. (1986) showed that N isotopic fractionation was related to the deamination and transamination of amino acids. Sick et al. (1997) conducted a feeding experiment with rats and found that plasma protein was enriched and plasma urea was depleted in 15N relative to the diet. Furthermore, Robbins et al

L, Cheng, RJ Dewhurst, J Larkin, F Buckley, C Thackaberry, AM Nicol, and GR Edwards

Proceedings of the New Zealand Society of Animal Production, Volume 70, Palmerston North, 65-66, 2010