Acetate Metabolism in the Ruminant.

Biochemists have long recognized the central role of acetate in the energy metabolism of most forms of life. But whereas for most organisms the supply of acetate, or rather its active form, acetyl coenzyme A, is almost entirely endogenous, ruminant animals have a large exogenous supply of acetate, which is produced in the rumen by microbial fermentation of ingested foodstuffs. In the ruminant, acetate, along with the other short chain fatty acids, particularly propionate and butyrate, provides the chief source of energy for the animal. Tolerance tests (l-3) have shown that the ruminant can metabolize the imposed load of large amounts of acetate. Previous isotope studies (4-7) indicate that the body pool of acetate turns over very rapidly and that the turnover rate, or acetate flux, when expressed as calories, represents a considerable proportion of the total energy requirement of the animal. As part of a continuing study of energy metabolism in ruminants we have used W-acetate to study the size and rate of metabolism of the acetate pool in fed sheep. To understand more fully the role of acetate in the energetics of the whole animal, we have examined the metabolism of both the methyl and the carboxyl carbons, and also the metabolism of acetate infused into a rumen vein as opposed to a jugular vein.