beta-Hydroxybutyrate and acetate metabolism of the perfused bovine udder.

It was established by Shaw and Knodt (I) that the normal lactating udder (in situ) of the cow utilizes almost 2 mg. of phydroxybutyric acid per 100 ml. of blood traversing the udder; it was calculated that this was sufficient to account for the short chain fatty acids of milk fat or for about 40 per cent of the oxygen consumption of the secreting gland if it were oxidized for energy purposes. Later work on ketotic cows (2) and perfused udders (3) showed that the utilization of this substrate by the lactating udder is greatly increased when the arterial levels are high. However, the ultimate fate of this substance within the mammary gland tissue remained uncertain. The importance of the lower aliphatic acids in ruminant metabolism has come to be recognized as a result of current interest in the metabolic activities of rumen microorganisms. In ruminants, acetate, propionate and butyrate are primary products of carbohydrate digestion and very little glucose, as such, is absorbed from the gut. The diurnal variations in the arterial levels of acetate are appreciable and the utilization of acetate by the udder is dependent on the arterial levels (4). Acetate is primarily incorporated by the perfused lactating ruminant udder into the volatile fatty acids characteristic of the ruminant milk fat (5). Butyrate, when injected intravenously, is incorporated to a lesser extent into milk fat, and participates in a net synthesis of carbohydrate in the ruminant (6, 7). This is a report on the incorporation of carboxyl-labeled phydroxybutyrate into milk components by a perfused udder, and on the effect of acetate on the utilization of fi-hydroxybutyrate by the perfused udder. A summary of some of the results of this study has been rep0rted.l