The effects of acute cold exposure and feeding on volatile fatty acid metabolism in the hind leg of the young ox

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Abstract
1. Young steers were fed either 20 or 4 h before exposure to a thermoneutral or a moderately cold environment. Measurements were made of total oxygen consumption (total VO2), respiratory quotient (RQ) and hind-leg blood flow (leg Q) and oxygen uptake (leg VO2). The arteriovenous difference in plasma concentrations of individual volatile fatty acids (VFA) across the leg was also measured. Net exchange and fractional uptake of VFA by the leg were calculated from these results.2. Cold exposure doubled total VO2, significantly decreased the RQ and caused 3-fold and 10-fold increases in leg Q and leg VO2 respectively in both 4 h- and 20 h-fed steers. Arterial plasma concentrations of total VFA (which was more than 95 % acetate) and net leg uptake of VFA also significantly increased in both groups. Cold had no effect on the fractional uptake of VFA by the leg.3. Feeding shortly before the experiment caused a significant increase in total VO2 in thermoneutrality only, and in RQ, arterial plasma VFA and net VFA uptake by the leg in both environments. There was a significant decrease in the fractional uptake of VFA by the leg.4. Calculations suggest that although circulating acetate could, in theory, supply over 60 % of the energy required by the hind leg in the resting, fed animal, less than 30 % of the increased requirement of the shivering leg could be supplied by acetate during acute cold exposure, even shortly after feeding.