THE EFFECT OF COLD EXPOSURE ON PLASMA LIPIDS OF THE NEW‐BORN AND ADULT OX

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Abstract
The plasma total free fatty acid (FFA) concentration of ten calves at birth was low, averaging 4·3 mg/100 ml. Five of these animals were exposed to an environment of +25°C immediately after birth, and their plasma FFA concentration increased significantly by 7·5 mg/100 ml. (P 〈 0·05) after the first hour of life. The other five animals were exposed to an environment of +5°C, and they also had a significant increase in plasma FFA concentration after the first hour of life, averaging 25·6 mg/100 ml. (P 〈 0·001). The increase in the group exposed to +5°C was significantly greater than the increase in the group exposed to +25°C (P 〈 0·001). No other plasma lipid fraction altered with change in environmental temperature.Five adult steers exposed to a thermoneutral environment (+15°C) had a mean plasma total FFA concentration of 10·7 mg/100 ml. at the end of 2 hr exposure. In a cold environment (−20°C) this was increased by 8·4 mg/100 ml. (P 〈 0·01) but no other plasma lipid fraction was altered.In one adult animal the adrenal glands were denervated and this had no effect on the increase of plasma FFA in the cold. The other 4 adults were injected with bethanidine, a sympathetic nerve blocking agent, and this reversed the change of plasma FFA concentration at −20°C and also reduced the increase in oxygen consumption which normally occurred at this environmental temperature.It is concluded from these experiments that the plasma FFA concentration of new‐born and adult oxen increases when they are exposed to a cold environment, and in the adult this increase is mediated through the sympathetic nervous system.

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