Bioavailability of zinc hydroxychloride relative to zinc sulfate in growing cattle fed a corn-cottonseed hull-based diet

A study was conducted to evaluate the bioavailability of zinc hydroxychloride (ZnOHCl) relative to Zn sulfate (ZnSO4) in growing steers. Sixteen Angus and Simmental steers (371 kg average initial weight) were fed a corn-cottonseed hull-based diet without supplemental Zn for 14 d. At the end of the 14-d depletion phase steers were randomly assigned within a breed to treatments consisting of supplemental Zn at 25 mg/kg DM from either ZnSO4 or ZnOHCl. Seven days after the initiation of Zn supplementation a 5-d total collection of feces and urine was conducted. Jugular blood samples were obtained on d 0 (prior to initiation of Zn treatments) and on d 40 of the study for plasma Zn determination. Dry matter intake, Zn intake and urinary Zn excretion were not affected (P > 0.10) during the metabolism phase. Apparent absorption and retention of Zn were greater (P < 0.01) in steers supplemented with ZnOHCl than in those supplemented with Zn SO4. Plasma Zn concentrations were similar across treatments on d 0 of the study. On d 40 of the study plasma Zn concentrations were higher (P < 0.05) in steers supplemented with Zn OHCl compared to those fed ZnSO4. Results of this study indicated that ZnOHCl is a more bioavailable source of Zn than ZnSO4 for growing cattle when supplemented to a diet with relatively low Zn bioavailability.