Experiments on the nutrition of the dairy heifer: I. Protein requirements of yearling stock

The literature on the protein requirements of young dairy heifers has been discussed and the wide variations noted, both in quantities estimated for particular live-weight ranges and in the suggested trends of requirements with live weight. Short-term trials have been conducted in which the effect of variation in protein intake on rate of live-weight gain of dairy heifers of various ages was studied. The response to increments of protein in the ration was found to be curvilinear with a rapid decline in response above critical levels of intake. This level varied with the live weight of the animal, being 0·8 lb. crude protein at 300 lb. live weight and 1·0 lb. at 400 and 500 lb. when rations based on hay, decorticated ground-nut meal and flaked maize were fed. These levels are somewhat lower than estimates of protein requirements quoted in the literature, though the trend indicated in them agrees with some of the published data. No marked difference was observed between the values of decorticated ground-nut meal and white fish meal as protein supplements. Urea was inferior to decorticated ground-nut meal. The overall depressant effect of straw on rate of live-weight gain is demonstrated and discussed.