Abstract
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 B12 injections. Forty-five primi- and multiparous cows at 60d 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 60d 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) 75mg/d of supplemental dietary Co from Co glucoheptonate (HCoGH), and (5) CON diet plus weekly 10mg i.m. of vitamin B12 injections (IB12). Cows remained on their respective treatment until 150d 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 B12 injections did not influence plasma or liver measures of energy metabolism. Injections of vitamin B12 increased plasma, liver, and milk vitamin B12 contents. Dietary Co addition did not affect plasma vitamin B12 concentrations; however, it did increase milk vitamin B12 concentrations throughout lactation and liver vitamin B12 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 B12 status on lactation performance. Overall, Co supplementation (inorganic and organic) or vitamin B12 injections improved measures of vitamin B12 status, but not lactation performance compared with CON possibly due to Co being above requirements in the CON diet.
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