386
Effect of a zinc injection on finishing performance and carcass characteristics of Limousin steers
The objective was to evaluate the effects of zinc injection at start of finishing on growth performance and carcass characteristics of steers, in experiments completed over two years. In experiment 1, Limousin steers (487.4 ± 45.5 kg, SD) blocked by initial BW (3 to 4 steers per pen), were assigned to one of two treatments: injection of zinc disodium EDTA (n = 20 steers) or sterile saline (n = 19 steers) on d 0 of the finishing period. Blood samples were collected on days 0, 5, 28, and 84 for blood glucose and alkaline phosphatase (ALP) analysis. In experiment 2, Limousin steers (571.2 ± 32.4 kg) blocked by initial BW (2 to 4 steers per pen), were assigned to the same treatments as experiment 1 (n = 22 zinc steers and n = 23 saline steers). Steers received a concentrate-based finishing diet, supplemented with 30 mg zinc/kg DM (ZnSO4) for 84 (experiment 1) or 56 d (experiment 2) and on average the zinc injection provided 381 mg zinc/steer. Ultrasound and carcass data were collected from all steers in both experiments. Data for both experiments were analyzed using the MIXED procedure of SAS, with year, treatment and the interaction as fixed effects. Steer was the experimental unit, except for DMI and G:F, where pen was the experimental unit. Treatment × year was not different for any variable (P ≥ 0.43). Zinc or saline injection did not affect final BW (1472, 1451 ± 14.8 kg, for saline and zinc, respectively), ADG, DMI, or G: F (P ≥ 0.25; G :F = 0.145, 0.138 ± 0.0046, for saline and zinc, respectively). Blood glucose and ALP were not affected by treatment × day (P > 0.40) or treatment (P > 0.22), but day affected glucose and ALP (P < 0.0001), as blood glucose concentrations decreased throughout the finishing period. Blood ALP levels decreased from d 0 to d 5 (P < 0.0001) but concentrations increased on d 28 (P < 0.0001). Ultrasound determined body composition included intramuscular fat, ribeye area, and backfat were not affected by treatment (P ≥ 0.27). Carcass characteristics including HCW, backfat, ribeye area, KPH, marbling score, and yield grade were not affected by treatment (P ≥ 0.22). Overall, a single injection of zinc in addition to dietary zinc supplementation at start of finishing had no effect on heavy Limousin steer performance or carcass characteristics.
Keywords: carcass, growth, Limousin, zinc