Crude Protein for Diets Fed to Weaned Dairy Calves

The concentration (as-fed basis) and source of protein in a diet for 4- to 12-wk-old weaned Holstein calves was evaluated. In Exp. 1, trial 1, 96 calves (8 wk old) were fed 1 of 4 diets containing 16% CP with soybean meal, 16% CP with soybean meal and modified expeller extracted soy protein, 18% CP with soybean meal, or 18% CP with soybean meal and modified expeller extracted soy protein, each blended with 5% hay in a 4-wk trial. There were no differences in performance because of CP concentration or source. In Exp. 1, trial 2, 96 calves (8 wk old) were fed either a 13.5, 15.0, 16.5, or 18.0% CP diet blended with 5% hay in a 4-wk trial. Calf ADG was maximized at 15% CP, whereas feed efficiency was maximized at 16.5% CP. In Exp. 2, 96 calves (4 wk old) were fed 1 of 2 diets arranged as 3 treatments in a 4-wk trial. The treatments were A) feeding a 16% CP diet for 4 wk, B) feeding an 18% CP diet for 2 wk followed by feeding a 16% diet for 2 wk, or C) feeding an 18% diet for 4 wk. No roughage was fed. Calf ADG tended to increase (4%) from treatments A through C. Diets for weaned calves should be 18% CP (63 g CP/Mcal ME) up to 8 wk old. Diets for calves from 8 to 12 wk old should be 15 to 16% CP (52 to 56 g CP/Mcal ME).