Effects of energy and protein allowances in the diets of prepubertal heifers on growth and milk production.

Sixty-one Italian Friesian heifers between 100 and 300 kg of body weight (BW) were fed one of four diets. Heifers that were fed the diet with low energy and low protein received 90% of the amounts of total digestible nutrients (TDN) and crude protein (CP) recommended by the National Research Council for large breed dairy heifers growing at a rate of 0.7 kg/d. Ninety and 110% of recommended amounts of TDN and CP, respectively, were supplied to heifers fed the diet containing low energy and high protein. The diet with high energy and low protein provided 110 and 90% of recommended amounts of TDN and CP, respectively, and heifers fed high energy and high protein received 110% of the recommended amounts of both TDN and CP. When heifers reached 300 kg of BW, all were fed an identical diet. Heifers were bred at approximately 370 kg of BW. The increase of either TDN or CP improved average daily gain (608.1 g/d for heifers fed the low energy and low protein diet; 658.9 g/d for heifers fed the low energy and high protein diet; 794.4 g/d for heifers fed the high energy and low protein diet; and 847.6 g/d for heifers fed the high energy and high protein diet). Milk production through 36 wk of the first lactation was not influenced by the increased TDN or CP in the diet (22.7 kg/d for heifers fed low energy and low protein, 22.2 kg/d for heifers fed low energy and high protein diet, 20.2 kg/d for heifers fed the high energy and low protein diet, and 21.8 kg/d for heifers fed high energy and high protein diet). Results showed that Italian Friesian heifers can tolerate an average daily gain of approximately 800 g from 100 to 300 kg of BW without any detrimental effect on future milk production.