CASE STUDY: Effect of feeding rate and weaning age of dairy calves fed a conventional milk replacer during warm summer months

Feeding rate of a 21% CP, 21% fat milk replacer (MR) and weaning age of Holstein dairy calves (initially 42 ± 1.1 kg of BW) were examined during summer months (averaging 24°C). In previous cool-weather (< 10°C) trials, feeding more MR has reduced starter intake and not increased ADG. In trial 1, the MR was fed to provide 3 MR feeding rates (0.44 kg daily for 28 d; 0.55 kg daily for 28 d; 0.66 kg daily for 14 d followed by 0.44 kg daily for 14 d). In trial 2, the MR was fed at 2 rates (0.44 and 0.66 kg/d) and calves were weaned at 2 ages (28 and 42 d) to provide 4 treatments. Measurements were made in individual nursery pens (fed MR) until 56 d and within group pens (no MR) for 56 more days. In each trial, ADG and hip-width change increased (P < 0.05) with more MR fed, but there was no difference (P > 0.05) in postweaning performance. Starter intake did not differ (P > 0.05) among MR rates and was low compared with other trials in this laboratory, likely because of heat stress. Feeding 0.66 kg of DM supported more (P < 0.05) ADG in calves weaned at 42 d verses 28 d. Feeding 0.66 kg of DM from a 21% CP, 21% fat MR increased ADG by as much as 19% versus feeding 0.44 kg of the same MR. Therefore, feeding 0.66 kg of DM from MR can serve as a tool to overcome some of the ADG lost during heat stress in young dairy calves.