Effect of factor B on vitamin B12 status and propionate metabolism in sheep.

Growing lambs fed diets containing two concentrations of Co (basal and basal plus 1 ppm) were injected with Factor B (cobinamide) or saline during an 8-wk trial conducted to determine the effects of Factor B on liver B12 levels and on propionate metabolism. At the end of the trial, lambs given Factor B had lower (P less than .05) liver vitamin B12 concentrations and higher (P less than .05) Factor B concentrations than controls fed the high Co diet. The high Co diet did not enhance liver B12 levels in the lambs treated with Factor B. Feed intake and body weight gain were not significantly affected by treatment. Plasma propionate increased (P less than .05) with time on experiment, and concentrations during the final period were negatively correlated (r = -.45; P less than .05) with liver B12 levels. When the lambs were loaded with propionate, a similar correlation (r = -.59; P less than .05) was observed between log plasma level at t = 20 and liver B12 levels. Liver B12 levels (.2 to 1.1 micrograms/g) were all within what is usually considered a normal range. . No significant relationship between plasma propionate and liver Factor B levels were observed.