The effect of protein content on the response of lactating cows to level of concentrate feeding

Abstract

SUMMARY: Seventy-two lactating dairy cows were used in a 4x 3 factorial experiment to assess the effects of the protein content of concentrates on the response to concentrate feeding level. Concentrates containing 12,18 and 24% crude protein in the dry matter were given at each of four levels of feeding: 0·25, 0·36, 0·47 and 0·58 kg/kg milk for a 7-week experimental period. Milk yield, milk energy output, liveweight change and the percentage solids-not-fat and protein in the milk were significantly affected by both the level of concentrate feeding and the protein content of the concentrate. Response curves for the effect of level of concentrate feeding on milk output and liveweight change were computed for each of the three protein levels, and although there was no significant interaction between these two main factors the benefit from increased protein in the concentrate was shown to depend partly on the level of feeding at which the concentrate was used. At low feeding levels the response to an increase in protein content of the concentrate tended to be smaller than that obtained at high feeding levels. At no stage was there any marked response to protein content in the concentrate above 18%. The response curves have been used to demonstrate the interchangeability of level of concentrate feeding and protein content of the concentrate as means of supporting a given level of milk production.