Differential responses to dietary cobalt in finishing steers fed corn-versus barley-based diets

An experiment was conducted to determine the effects of dietary Co concentration on performance, carcass traits, and plasma, liver, and ruminal metabolites of steers fed corn- or barley-based diets. Sixty steers, initially averaging 316 kg, were stratified by BW and assigned randomly to treatments in a 2 x 3 factorial arrangement, with factors being a corn- or barley-based diet and supplemental Co added at 0, 0.05, or 0.15 mg/kg of DM. Control corn-and barley-based diets analyzed 0.04 and 0.02 mg of Co/kg of DM, respectively. Steers were fed individually using electronic Ca-lan gate feeders. Cobalt supplementation increased (P < 0.05) DMI and ADG over the total study. From d 85 to finish, Co supplementation increased (P < 0.05) ADG by steers fed corn- but not barley-based diets. The G:F was increased (P < 0.05) by Co supplementation during the first 84 d but not over the entire finishing period. Average daily gain and G:F were greater (P < 0.05) for corn- vs. barley-fed steers. Supplemental Co increased vitamin B-12 in plasma and liver (P < 0.05), and plasma vitamin B-12 was greater (P < 0.05) in steers fed corn- vs. barley-based diets. Cobalt supplementation increased (P < 0.05) ruminal fluid vitamin B-12 on d 84 in steers fed corn- but not barley-based diets. Folate was greater in plasma (P < 0.01) and liver (P < 0.05) of steers fed Co-supplemented diets. Increasing supplemental Co from 0.05 to 0.15 mg of Co/kg of DM increased (P < 0.05) liver folate in steers fed barley- but not corn-based diets. Supplemental Co decreased (P < 0.01) plasma methylmalonic acid concentration in steers. Increasing supplemental Co from 0.05 to 0.15 mg/kg of DM decreased plasma and ruminal succinate concentrations, and steers fed barley-based diets had greater (P < 0.05) plasma and ruminal succinate relative to those fed corn-based diets. Addition of supplemental Co to the basal diets increased (P < 0.01) plasma glucose concentrations of steers, and steers fed corn-based diets had greater plasma glucose than those fed barley-based diets. Steers supplemented with Co had greater ruminal propionate (P < 0.01) and lesser (P < 0.05) ruminal acetate and butyrate proportions than controls. Supplemental Co increased dressing percent (P < 0.10) and HCW (P < 0.01) at slaughter. These results indicate that feeding steers corn- or barley-based diets deficient in Co adversely affects performance and vitamin B-12 status.