Acetate metabolism in the mammary gland of the lactating ewe

Acetate metabolism in the mammary gland of lactating ewes was studied by continuous infusion of radioisotopic [U-14C]sodium acetate and measurement of mammary gland arteriovenous difference and blood flow. Entry rate of acetate into the whole body averaged 75 +/- 7 mumol min-1 kg-1 liveweight and 22.1 +/- 2.7% of total CO2 production was derived from acetate. Acetate was both utilized and produced by the mammary gland. Acetate uptake was related linearly (r2 = 0.94) to arterial concentration and gross utilization of acetate accounted for 16.2 +/- 2.6% of whole-body entry rate. Endogenous acetate production by the mammary gland increased linearly (r2 = 0.90) as milk yield rose, and accounted for 25.6 +/- 2.7% of the gross mammary utilization of acetate. The proportion of mammary CO2 derived from acetate (22.5 +/- 3.9%) was similar to that of the whole body. The uptake of acetate, 3-hydroxybutyrate, esterified fatty acids and plasma free fatty acids accounted for about 25, 13, 60 and 4% of milk fatty acid carbon respectively, after correction for the oxidation of acetate, but not of the other substrates. Metabolism of acetate in the mammary glands of lactating ewes appears quantitatively more important than that in cows, but similar to that in goats.