Interaction of early metabolizable protein supplementation and virginiamycin on feedlot growth-performance and carcass characteristics of calf-fed Holstein steers
Abstract One hundred sixty-eight Holstein steer calves (133.4 ±7.9 kg) were used to evaluate the influence of virginiamycin (VM) supplementation on cattle growth performance and liver abscess incidence, and the effect of feeding 100% vs 87% of metabolizable protein (MP) requirements during the initial 112 d on growth performance, efficiency of energy utilization, and carcass characteristics. Steers were balanced by weight and assigned to 28 pens (6 steers/pen). During the initial 112-d feeding period, dietary treatments consisted of two levels of metabolizable protein (100 vs 87% of expected requirements during the initial 112 d feeding period; NASEM, 2000) supplemented with or without 22.5 mg/kg virginiamycin (Phibro Animal Health, Teaneck, NJ 07666) in a 2×2 factorial arrangement. There were no VM × MP supplementation interactions (P ≥ 0.14) on any of the parameters measured in both experiments. Calf-fed Holstein steers supplemented VM increased (P ≤ 0.03) overall ADG, G:F, observed/expected NE values for maintenance and gain, and final body weight (BW). Cattle fed VM also increased (P ≤ 0.04) carcass weight, dressing percent, and longissimus muscle area. However, there was no effect (P ≥ 0.22) of VM supplementation on any other carcass characteristics. Calf-fed Holstein steers fed 100% MP requirements during the initial 112 d feeding period had greater (P ≤ 0.02) ADG, G:F, observed/expected NE values for maintenance and gain, and live BW compared to steers fed 87% of the expected metabolizable protein requirements. However, there was no effect (P ≥ 0.17) of MP supply during the initial 112-d period on overall (342 d) growth performance measurements. The incidence of liver abscesses was low (averaging 7.7%) and not affected by dietary treatments. We conclude that independently of MP supplies, supplemental VM enhances overall growth performance and efficiency of energy utilization of calf-fed Holstein steers.