Cobalt supplementation, alone or in combination with vitamin B and selenium: Effects on lamb performance and mineral status.

The effects of supplementing lambs with Co, either alone or in combination with vitamin B and Se, were evaluated over the period from weaning to selection for slaughter. Two hundred and five recently weaned (at 14 wk [SD 0.44] of age), spring-born lambs of various crossbred genotypes were stratified, within genotype, by BW and gender and allocated to 3 groups, which were then allocated at random to one of the following treatments: no supplement (Control), a supplement containing Co only (Co-only), or a supplement containing Co, vitamin B, and Se (VitMin). The concentration of Co in the Co-only supplement was 2.1 mg/mL (as cobalt sulfate); the VitMin supplement contained Co (10 mg/mL, as cobalt acetate), vitamin B (200 μg/mL), and Se (0.25 mg/mL, as sodium selenite). Lambs on the Co-only and VitMin treatments received, every 14 d, 10 and 2.1 mL, respectively, of oral drench. Lambs were managed in a rotational-grazing system from 12 July (swards predominantly ) and selected for slaughter, on the basis of BW, after 45, 73, or 115 d; all remaining lambs were slaughtered on d 157. Supplementation, with Co-only or VitMin, increased BW at slaughter ( < 0.01), ADG ( < 0.001), carcass weight ( < 0.001), dressing percentage ( < 0.001), carcass fat score ( < 0.05), and the proportion selected for slaughter by d 73 ( < 0.05) and 115 ( < 0.01). Relative to the Control, the benefit to ADG from supplementation increased as the season advanced. Therefore, supplementation did not alter ( = 0.82) ADG between d 1 and 45 but increased ADG over the intervals d 45 to 73 ( < 0.01), d 73 to 115 ( < 0.001), and d 115 to 157 ( < 0.001). There was no difference ( > 0.05) between the Co-only and the VitMin treatments for ADG, carcass weight, fat score, or dressing percentage. Supplementation with Co increased liver Co concentration ( < 0.001), and lambs supplemented with VitMin had greater liver Co concentration than lambs supplemented with Co-only ( < 0.05); the concentrations were 0.18, 0.85, and 1.18 μmol/L for the Control, Co-only, and VitMin treatments, respectively. Treatment had no effect ( = 0.65) on the concentration of Se in kidney tissue. It is concluded that supplementation with Co increased lamb performance after weaning, that response to supplementation increased as the grazing season progressed, and that no extra benefit in performance resulted from augmenting supplementary Co with B and Se.