Cobalt Requirements of Growing and Finishing Cattle Based on Performance, Vitamin B12 Status and Metabolite Concentrations.

Abstract

Experiments were conducted to determine cobalt requirements for growing and finishing beef cattle, compare the relative bioavailability of different cobalt sources, and evaluate the effects of cobalt on ruminal fermentation. During experiments 1 and 2 steers were fed corn-cottonseed hull-soybean meal-based growing diets, followed by high concentrate finishing diets (diets contained approximately 0.05 mg Co/kg). Dietary treatments for experiment 1 consisted of 0, 0.05, 0.10 and 1.0 mg of supplemental Co/kg DM from CoCO3 or 0.05 and 0.10 mg of supplemental Co/kg DM from Co propionate (CoPr). Treatments were similar for experiment 2 with the exception that the Co supplemented at 1.0 mg/kg was as CoPr instead of CoCO3. Performance was not affected by cobalt source or supplementation during the growing phase of either study. However, cobalt supplementation to the finishing diet increased feed intake, average daily gain, plasma and liver vitamin B12, and plasma glucose, and decreased plasma methylmalonic acid. Supplemental cobalt increased ruminal propionate proportions during the finishing phase, and steers supplemented with CoPr had higher ruminal propionate relative to those supplemented with CoCO3 during the growing phase.

During the third study the effects of supplementing cobalt to corn or barley-based finishing diets were evaluated in steers. Supplemental cobalt increased intake, gain, and vitamin B12 and folate status of finishing steers. Steers fed barley gained less, had lower ruminal, plasma, and liver vitamin B12, lower plasma and liver folate, and lower plasma glucose relative to those fed corn-based diets.

In the final study, in vitro fermentation characteristics of ruminal microbes fed corn-based diets supplemented with cobalt were evaluated. Within three days, cobalt supplementation resulted in a substantial increase in microbial vitamin B12 production. In addition, ruminal succinate concentrations of the unsupplemented control cultures increased sharply suggesting that the vitamin B12-dependent enzymatic conversion of succinate to propionate had been affected. Based on performance, vitamin B12 status, and metabolite concentrations, 0.15 mg/kg of total dietary cobalt is required for finishing steers.