Composition of growth of Holstein calves fed milk replacer from birth to 105-kilogram body weight

Sixty calves were assigned to a comparative slaughter study to determine th e changes in composition of milk replacer-fed Holstein bull calves from bir th to 105-kg body weight (BW). Six calves were slaughtered on day of birth and served as a baseline for comparison of compositional changes. Fifty-fou r calves were assigned to one of three treatments (18 calves per treatment) . Calves were fed milk replacer containing 30% crude protein (CP) and 20% f at. Target growth rates for treatments 1, 2, and 3 were 500, 950, and 1400 g/d, respectively. Six calves from each treatment were slaughtered and anal yzed for energy, nitrogen, ether extract, and ash when they reached 65, 85 and 105 kg of BW. Actual daily gains from birth to slaughter were 560, 973, and 1100 g, and net deposition of CP and fat were 140 and 44, 204 and 154, and 247 and 161 g/d for treatments 1, 2, and 3, respectively. Results were used to develop equations to predict retained energy [retained energy = (e mpty BW0.223) X (empty BW gain(132))], and retained protein, [retained prot ein = (184 X empty BW gain (kilograms/d)) + (17.2 X (retained energy)/empty BW gain] where retained energy is in Mcal/d, retained protein is in g/d, a nd empty BW and gain are in kilograms. The composition of gain observed was compared to predictions from the 1989 Dairy NRC and 1996 Beef NRC equation s and demonstrated the equations do not represent the composition of gain i n calves of this weight.