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

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.

Determination of volatile fatty acids in plasma after ethanolic extraction

1. A new rapid micro-method for measuring plasma volatile fatty acids is described. The volatile fatty acids are extracted from plasma with ethanol in the presence of a known quantity of internal standard (sodium isobutyrate). After evaporation of the ethanolic solution of the sodium salts, the residue is dissolved in a dilute solution of orthophosphoric acid to permit analysis by g.l.c. 2. A technique of g.l.c. analysis is described which permits the separation of all the volatile fatty acids from the other plasma constituents at temperatures below 100 degrees C in 5 min. 3. Steam-distillation techniques are unsatisfactory when the acetic acid concentrations in the plasma are below 0.2mm. Heating of a number of plasma constituents in acid conditions gives rise to acetic acid. 4. The binding of volatile fatty acids to plasma proteins was studied; this binding is negligible for acetic acid, but increases with the length of the fatty acid carbon chain. 5. The limits of use of the method and the physiological implications are discussed.

Diurnal patterns of plasma insulin, growth hormone, corticosteroid and metabolite concentrations in fed and fasted sheep

To determine the effects of feeding on plasma concentrations of insulin and growth hormone (GH) in sheep during the full 24 h of the normal feeding cycle, two experiments have been conducted on a group of 18 crossbred wethers.

Early changes in plasma insulin and growth hormone levels after feeding in lambs and adult sheep

When lambs 1-3 months of age ingested 250 or 500 m1 of milk by sucking vigorously from a teat, there was a rapid increase in their plasma insulin concentration to a maximum 5 min after starting to suck. At the same time plasma growth hormone (GH) levels declined rapidly. Changes of comparable magnitude were also seen when lambs drank milk diluted with water or vigorously ate chopped lucerne hay, when adult wether sheep ate dry feed rapidly, and when an adult wether fitted with an oesophageal fistula was 'sham-fed'. The changes were not seen when sheep, although offered food, did not eat. These responses were not closely related to changes in plasma glucose or ",-amino nitrogen concentrations and they evidently involve reflex nervous mechanisms.

Effects of feeding a zero- or high-roughage diet to cattle upon adipose tissue lipogenesis

Hereford steer calves were fed whole shelled corn or corn silage diets to determine the effect of dietary roughage level on lipogenic enzymes of adipose tissue. In Trial 1, perirenal and subcutaneous adipose tissue were taken post-mortem from 32 steers who had been fed either diet ad libitum for at least 175 days and weighed 450 kg live. In Trial 2, for which a changeover design was used, six cattle were fed both diets so that energy intake was calculated to be equal for each. Perirenal adipose tissue was taken in the second trial by biopsy when the steers weighed 200 kg live. In Trial 1, compared to high-roughage, the zero-roughage diet elicited from a two- to fourfold increase (P < 0.05) in activity of pentose phosphate pathway dehydrogenases of adipose tissue. This dietary effect was not observed in Trial 2. In both trials, acetyl-CoA synthetase activity and fatty acid synthesizing capacity from acetate of adipose tissue were unaffected by diet. Carcasses from animals fed the zero-roughage diet in Trial 1 contained 6% more separable fat (P < 0.05) than carcasses from animals fed the high-roughage diet. The mean of both trials for plasma acetate from animals fed the zero-roughage diet was 0.61 μmol/ml, which was less (P < 0.05) than 0.95 μmol/ml, which was the comparable value determined from animals fed the high-roughage diet. Plasma propionate was increased (P < 0.05) by feeding the zero-roughage diet in both trials but accounted for less than 20% of volatile fatty acids in all samples examined.