Effect of micronutrient source on mineral status and performance of steers fed low or high sulfur diets

Abstract Text: The objective was to determine effects of hydroxy (HYD) or inorganic (ING) trace minerals within low or high S diets on mineral status and performance of beef steers. Forty-eight Angus-crossbred steers were blocked by BW (316 ± 2.8 kg) and assigned to a 2 x 2 factorial with low (0.25%; LS) and high S (0.53%; HS; additional S as CaSO₄). Trace minerals (TM) were supplemented as 10 mg Cu, 30 mg Zn, and 20 mg Mn/kg DM from ING (sulfates) or HYD (IntelliBond; Micronutrients USA LLC, Indianapolis, IN). Growing period (GP, 84 d) diets were corn-silage based and finishing period (FP, 78 d) diets were corn-based with 12% hay. Steers (6 per pen) were fed via GrowSafe bunks and experimental unit was steer (n = 12 per treatment). Plasma and liver mineral concentrations were determined at trial initiation and end of GP and FP. Data were analyzed as a 2 x 2 factorial using SAS; initial plasma and liver mineral concentrations were covariates in analysis. High S decreased (P < 0.01) end of GP and FP liver Cu concentrations, while tending (P ≤ 0.1) to decrease plasma Cu at these times. At end of GP HS decreased (P = 0.04) plasma Zn concentrations and tended to decrease (P = 0.1) liver Zn concentrations. Final liver Cu concentrations were greater in ING steers than HYD (P < 0.01). Liver Mn concentrations displayed S x TM effects (P = 0.05) at the end of GP and FP, where LS-HYD had greater Mn concentrations than HS-HYD, HS-ING, and LS-ING at end of GP; however, HS-HYD final Mn concentrations tended to be greater than LS-HYD and LS-ING tended to be greater than HS-ING and LS-HYD. Growing period ADG and G:F displayed TM x S effects (P ≤ 0.06) where LS-HYD had better efficiency and gain than LS-ING and HS-ING. Overall, HS-HYD was less efficient than HS-ING (P = 0.02) and LS-HYD (P = 0.06). Overall DMI, ADG, final BW, HCW, and marbling scores were not different (P ≥ 0.12) due to treatment; however, steers consuming ING had larger REA (P = 0.02) than those fed HYD, and HS decreased (P = 0.03) backfat and yield grade compared to LS.  In this study HS decreased markers of Cu and Zn status, and differential effects of ING vs HYD minerals were noted, though all steers maintained adequate status.

Keywords: beef, sulfur, trace mineral