Some metabolic aspects of vitamin B 12 deficiency in sheep.

I. Studies were made with pair-fed vitamin Blz-deficient and vitamin B12-treated or cobalt-treated ewes fed a Co-deficient diet in cages. Measurements were made of body-weight changes and some observations were made of energy and nitrogen metabolism. The effects of oral Co on energy and nitrogen metabolism were examined in sheep fed the Co-deficient diet, but not yet deficient of vitamin B,, in the tissues. 2. The rate of loss of body-weight of vitamin B,,-deficient sheep was significantly faster ( P < 0.01) than that of pair-fed sheep given 50 pg vitamin Blz/d by injection. 3. In a limited number of observations of pair-fed sheep no significant differences were found in retention of combustible energy from the diet, but excretion of faecal nitrogen was higher in deficient animals than in animals receiving vitamin Blz or Co. 4. There was no significant effect of supplementary Co on energy metabolism, nitrogen metabolism, production of methane or digestibility of fodder in sheep that were not deficient of vitamin BIZ.