Estimating diet nitrogen use efficiency from isotopes of tail hair in cattle

Cattle grazing tropical rangelands often have to depend on N-deficient pastures during prolonged dry seasons. Thus the ability of individual animals to best utilize the available diet N (i.e. N use efficiency; NUE) is likely directly related to performance. As tail hair grows amino acids are incorporated into hair proteins, and the relative abundance of the 15N and 14N isotopes (15Ntailhair) reflect a number of factors, including diet. Animals with higher NUE may have lower 15Ntailhair, apparently because of lower urinary N excretion (Cantalapiedra-Hijar et al. 2015). Estimation of NUE from tail hair has obvious advantages for practical on-farm sampling. This study evaluated whether NUE was related to 15Ntailhair in Bos indicus cattle typical of northern Australia.