Dietary protein levels and blood composition of dairy cattle

Abstract

The protein requirements of farm animals cannot be considered in isolation from their energy requirements and studies on changes in blood composition due to changes in protein intake must be made with defined and preferably constant energy intake. Two experiments have been carried out in which groups of permanently housed cattle have been fed individually different levels of dietary protein while all were receiving the energy intakes recommended by the Agricultural Research Council (ARC, 1965).In the first experiment the basic diet consisted of 6.8 kg hay and 1.8 kg concentrates of either 15.1 per cent digestible crude protein (DCP, high protein) or 6.8 per cent DCP (low protein), fed at 0.4 kg/kg milk produced. The peak milk yield was 13.5 kg/day and at peak yield, the daily metabolizable energy (ME) intake was 130 MJ in both groups. This experiment has been fully reported by Manston, Russel, Dew and Payne (1975).