Effect of vitamin B12 status on performance of the lactating ewe and gluconeogenesis from propionate

Ewes fed a diet containing .06 ppm cobalt prior to and after parturition were used to examine effects of hydroxycobalamin supplementation upon production of milk. Four ewes were assigned to each of three treatments after hand milking at 3 wk postpartum. At 7 wk postpartum, B12 concentrations in liver were enhanced in the group receiving intramuscular injections of 200 micrograms on alternate days (750 ng/g wet liver) relative to low groups that received 20 and 0 micrograms on alternate days (190 and 200 ng/g wet liver). Following 1 wk of treatment, B12-enhanced ewes had greater daily intake of feed and increased live weight. Vitamin B12 status was without significant effect on production of milk, total solids, fat, and solids-not-fat at 4, 5, and 6-wk milkings; however, production of milk protein was increased for B12-enhanced ewes. After lactations were terminated and feed intakes standardized, slices of liver obtained from B12-enhanced ewes incorporated 2-carbon 14-labeled propionate into glucose at rates greater than did slices from low B12 ewes. Subclinical changes affecting production may occur in lactating sheep when B12 status is at the lower end of what usually is considered the normal range.