Effect of Weaning Age of Dairy Calves Fed a Conventional or More Optimum Milk Replacer Program

Comparisons of different weaning ages of calves fed high-protein, high-feeding-rate milk replacer (MR) programs have not been reported in the literature. Thus, the objectives of these trials were to compare the performance of calves fed either a conventional MR [0.454 kg of a 22% CP, 20% fat (as fed) MR powder daily; MR A] or a more optimum MR [0.681 kg of a 26% CP, 17% fat (as fed) MR powder daily; MR B] and weaning them at either 28 or 42 d. Trial 1 evaluated the weaning age of calves fed MR A or B. Trial 2 compared the weaning age of calves fed MR B. Holstein calves were fed an 18% CP starter and fresh water ad libitum throughout the 56-d trials. In trial 1, calves fed MR B had 50% greater ADG, consumed 24% more starter, were 13% more efficient, and had 68% more hip width change than calves fed MR A (P < 0.05). Calves weaned at 28 d consumed 36% more starter than calves weaned at d 42 (P < 0.05). In trial 2, calves weaned at 28 d consumed 25% more starter than calves weaned on d 42 (P < 0.05). Weaning age did not affect BW gain by 56 d in either trial. A meta-analysis of published data using MR B revealed that weaning age did not change ADG through d 56, but calves weaned at 28 d consumed more starter and had a lower feed efficiency than calves weaned at 42 d.