9Paterson J E. Macpherson A. A comparison of serum VitaminB12 and serum methylmlonic acid diagnostic measures of cobalt status in cattle. The Veterinary Record,1990, (7) :329 -332.
10Hurley W. L, et al. Recent developments is the roles of vitamins and minerals in reproduction. J DairySci , 1989 ,72 (2 -3) :784-804.
