Adaptations to ambient temperature in growing pigs

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Abstract
Pigs were weaned at 8–10 days of age and littermate pairs were raised in individual cages at ambient temperatures of 25°C or 35°C to 8 weeks of age. Pigs reared at the higher temperature had longer extremities and less hair than controls even though body weights were similar. On exposure to an ambient temperature of 45°C, the animals reared in the cooler environment increased rectal temperature twice as quickly as their littermates. When the scrotum was heated locally to 42°C animals reared in the warmer environment began to pant at a lower ambient temperature than the controls. Heating the hypothalamus by means of an implanted thermode at an ambient temperature of 35°C was accompanied by an increase in respiratory frequency in pigs reared at 25°C. The pigs reared at 35°C already had a slightly elevated rate of breathing and heating the hypothalamus caused no change. The rate of blood flow in the tail was higher in pigs reared at 25°C than those kept at 35°C when measured at ambient temperatures between 20°C and 35°C. When the hypothalamus was cooled the slope of the line relating blood flow to the temperature of the thermode was similar in both groups. The critical temperature as determined from measurements of oxygen consumption was higher in the pigs reared at 35°C than in controls. But the effect of cooling the hypothalamus on metabolism was similar in both groups. There was no difference between the two groups in the rate of cutaneous water loss.