Influence of dietary cobalt source and concentration on performance, vitamin B12 status, and ruminal and plasma metabolites in growing and finishing steers.

Abstract

Sixty Angus steers, averaging 274 kg, were used to evaluate the effects of Co source and concentration on performance, vitamin B12 status, and metabolic characteristics of steers. Treatments consisted of 0 (control, analyzed 0.04 mg Co/kg), 0.05, 0.10, and 1.0 mg of supplemental Co/kg of DM from CoCO3 or 0.05 and 0.10 mg of supplemental Co/kg of DM from Co propionate. Steers were individually fed a growing diet for 56 d followed by a high-concentrate finishing diet. Performance was not affected by Co supplementation during the growing phase. During the finishing phase, ADFI (DM basis) and ADG were higher (P < 0.05) for the entire finishing phase, and gain:feed was higher (P < 0.10) over the first 56 d for Co-supplemented steers. Steers supplemented with 0.10 mg Co/kg as Co propionate had higher (P < 0.05) ruminal propionate and lower (P < 0.05) acetate molar proportions than steers receiving 0.10 Co/kg as CoCO3 during the growing phase. Supplemental Co increased (P < 0.10) molar proportion of propionate during the finishing phase. Plasma vitamin B12 was higher (P < 0.05) in Co-supplemented steers by d 56 of the growing phase and remained higher (P < 0.10) throughout the study. Control steers had higher (P < 0.05) plasma methylmalonic acid on d 56 of the growing phase and on d 28, 56, and 112 of the finishing phase than steers receiving supplemental Co. Steers supplemented with Co had higher plasma glucose at d 56 (P < 0.01), 84 (P < 0.10), and 112 (P < 0.01) of the finishing phase. Steers supplemented with 0.10 mg Co/kg as Co propionate had higher plasma glucose than those receiving 0.10 mg Co/kg as CoCO3 at d 28 of the growing phase (P < 0.05) and d 28 of the finishing phase (P < 0.10). Final body weight and hot carcass weight were lower (P < 0.10) in steers receiving the control diet, whereas other carcass characteristics were not affected by dietary Co. Average daily gain and feed efficiency for the entire finishing phase did not differ among Co-supplemented steers. However, increasing supplemental Co above 0.05 mg/kg DM (total diet Co = 0.09 mg/kg) resulted in increased (P < 0.01) plasma (linear) and liver (quadratic) vitamin B12 concentrations and decreased (quadratic, P < 0.10) plasma methylmalonic acid concentrations toward the end of the finishing phase. These results suggest that finishing steers require approximately 0.15 mg Co/kg of DM. Vitamin B12 status was not affected by Co source; however, the two Co sources seemed to affect certain metabolites differently.