Acetate metabolism in lactating sheep.

1. The metabolism of acetate, glucose and D(-)-3-hydroxybutyrate was studied in lactating and non-lactating sheep in vivo. Special consideration was given to the utilization by hind-limb muscle in both groups of sheep and the uptake of nutrients by the lactating mammary gland was also measured. 2. The entry of acetate into the circulation (mmol/h per kg body-weight) was similar in all experimental animals at a given arterial concentration of acetate. However, normal lactation was associated with a reduced extraction of acetate by muscle and the 'spared' acetate was comparable with that removed by the udder. Feeding lactating ewes a 700 g concentrate/kg ration tended to prevent this redistribution of acetate utilization. 3. The muscles of non-lactating ewes utilized sufficient glucose, when corrected for lactate release, to account for 57% of the oxygen utilization by muscle. In lactation this fell to 32% largely because of an increased lactate production. D(-)-3-Hydroxybutyrate utilization by muscle accounted for 16-17% of the O2 consumed by the muscle in non-lactating and lactating sheep. 4. Lactating mammary gland metabolism in sheep was similar to published values for dairy cows and goats. Thus the extraction (%) of glucose, O2, acetate and D(-)-3-hydroxybutyrate was 25, 28, 62 and 53 respectively. Blood flow was 529 ml/min per kg udder and the ratio, blood flow: milk flow was 475. glucose used by the udder relative to the whole animal utilization rate may be less in sheep than in cows and goats, but the comparable proportion for acetate is as large or larger than in these species.