The effect of early-weaning rations upon the efficiency of growth and carcass production with some observations on the development of forestomachs in calves

The live-weight gain, efficiency of food conversion, energy and nitrogen accretion as edible carcass, and the forestomach development were measured in three groups of calves fed for 10 weeks (days 19-89 of life) either a diet of 4-5 1 of milk daily, or a concentrate meal containing 4% sodium propionate ad libitum, or a concentrate meal ad libitum. All groups had access to lucerne chaff and water ad libitum. The mean live-weight gains of the three groups of calves were 47-5, 36'6 and 37-1 kg respectively even though their total energy and nitrogen intakes were not significantly different. The provision of dietary propionate did not improve the efficiency of food conversion or of energy or nitrogen accretion as the calves ate less of the meal containing propionate and more lucerne chaff. The differences in live-weight gain could be accounted for by the differences in carcass weight. Associated with the higher live-weight gain was a much higher efficiency of food utilization and of edible carcass energy and nitrogen accretion. The superior efficiency of the unweaned calves was concluded to be due to the liquid portion of the diet by-passing the rumeno-reticulum into the abomasum where the efficiency of utilization of highly digestible protein and carbohydrate is greater. The concentrate plus propionate fed calves ate less concentrate but more chaff and had a lower efficiency of food utilization and edible carcass energy accretion than the other weaned group of calves. The weight of rumeno-reticular tissues was greater in the weaned than in the unwearied calves, although the meal plus propionate group ate similar quantities of chaff to the unweaned group. In all groups, the degree of papillary development was related to the intake of concentrates plus roughage. The most appropriate manner to describe ruminal tissue weight is discussed