Effects of cobalt supplementation and vitamin B12 injections on lactation performance and metabolism of Holstein dairy cows

The objective of this study was to determine lactation performance and metabolism of primiparous and multiparous dairy cows fed different levels and sources (inorganic and organic) of Co or given weekly vitamin B(12) injections. Forty-five primi- and multiparous cows at 60 d prepartum were blocked by expected calving date, and randomly assigned to 1 of 5 treatments in a randomized complete block design with treatments starting at 60 d prepartum. The 5 treatments were (1) no supplemental dietary Co (control, CON), (2) 25mg/d of supplemental dietary Co from Co carbonate (CoCarb), (3) 25mg/d of supplemental dietary Co from Co glucoheptonate (LCoGH), (4) 75 mg/d of supplemental dietary Co from Co glucoheptonate (HCoGH), and (5) CON diet plus weekly 10mg i.m. of vitamin B(12) injections (IB12). Cows remained on their respective treatment until 150 d after calving. Cobalt concentrations (mg/kg of dry matter) in the lactating diets were 1.0, 1.9, 2.3, and 5.1 for CON/IB12, CoCarb, LCoGH, and HCoGH, respectively. Dry matter intake, body weight, and body condition score were not affected by treatment. The LCoGH treatment tended to have greater milk yield than CoCarb, and CON had similar milk yields to the mean of LCoGH and HCoGH. Cobalt supplementation or the use of vitamin B(12) injections did not influence plasma or liver measures of energy metabolism. Injections of vitamin B(12) increased plasma, liver, and milk vitamin B(12) contents. Dietary Co addition did not affect plasma vitamin B(12) concentrations; however, it did increase milk vitamin B(12) concentrations throughout lactation and liver vitamin B(12) at calving with no effect of source or level of Co. Folate status of cows in the study was low and possibly limited the effect of improved vitamin B(12) status on lactation performance. Overall, Co supplementation (inorganic and organic) or vitamin B(12) injections improved measures of vitamin B(12) status, but not lactation performance compared with CON possibly due to Co being above requirements in the CON diet.