Effects of environmental temperature on food intake in growing pigs.

l. The food intake of forty-seven young growing pigs has been measured during exposure to cold, thermoneutral and warm ambient temperatures. In some experiments the pigs were allowed to feed from an open bowl and in others they performed an operant response to obtain food. 2. When the pigs were housed at a thermoneutral temperature and transferred once a day to a high or low temperature before feeding, food intake was not affected. When the same pigs had to make an operant response for food they ate less in the hot environment. 3. Pigs kept at 20°C and fed once a day by operant conditioning at 5, 20 or 35°C ate less at 35°C than at 2O”C, but there was no difference in intake between 5 and 20°C. If pigs were exposed for 2 or 4 hr to 5, 20 or 35°C before they were fed, then food intake in the cold environment increased, but the decrease in food intake in the hot environment was less apparent. 4. Measurement of food intake over 24 hr periods at various temperatures revealed a circadian rhythm with maximum intake diurnally. Changing the ambient temperature from thermoneutral to warm was accompanied by a transitory decrease in food intake; changing from thermoneutral to cold was accompanied by a sustained rise in intake.