Production within the rumen and removal from the blood-stream of volatile fatty acids in sheep given a diet deficient in cobalt

1. The production and metabolism of volatile fatty acids were studied in sheep offered a cobalt-deficient diet.

2. The molar proportions of acetic (60%), propionic (26%) and butyric (14%) acids in the rumen fluids of sheep given the Co-deficient diet, but whose stores of vitamin B12were adequate, were similar before and after administration of an oral supplement of Co.

3. In pair-fed sheep, one member of which was vitamin B12-deficient and the other (control) treated with vitamin B12parenterally, the concentrations after feeding of both total and individual volatile fatty acids in the blood tended to be higher in deficient than in control sheep.

4. Following injection of the respective salts of individual volatile fatty acids into the blood-stream, formate clearance was apparently not affected, whereas that of acetate was slightly, and that of propionate very significantly, delayed in vitamin B12-deficient sheep compared with pair-fed control animals.

5. Acetate metabolism was retarded in the presence of propionate; the effect was greater in deficient than in pair-fed control sheep.

6. The hypothesis is advanced that it is the failure to metabolize propionate at the normal rate that leads to the progressive loss of appetite in vitamin B12-deficient sheep.