Heat Production and Respiratory Quotient Changes with Food Intake in Swine

ABSTRACT PIGS (25 to 57 days old and fasted for 15 hr) were individually exposed to air temperatures of 15, 25 and 35 °C. After monitoring baseline data, each pig was either fed or sham fed and data collection was continued until dynamic responses to feed intake ceased. Data collection included rectal and eight skin surface temperatures, oxygen consumption, carbon dioxide production, respiratory evaporative water loss and respiratory frequency. Following feed intake at 35 °C (mild heat stress) heat production was increased approximately 30 percent above baseline values between 15 and 120 min post-feeding. At 15 °C (cold stress) and 25 °C (mild cold stress) rapid initial increases in heat production were observed following both feed-ing and sham feeding. These increases rapidly de-clined to prefeeding levels within 45 min and were attributed to the increased metabolism required for body temperature regulation. At all air temperatures increases in the respiratory quotient began approximately 25 min post-feeding and reached a plateau at a new higher level between 45 and 80 min post-feeding and then declined to prefeeding levels. Follow-ing feed intake at all ambient temperatures, rectal temperature increased 0.25 to 0.5 °C above prefeed-ing levels. Rectal temperatures remained elevated at these higher levels throughout the durations of these tests; however, all other measured thermoregulatory parameters returned to their prefeeding, baseline values.