Upper Critical Temperature of Iberian Pigs.

The effect of ambient temperature on various physiological parameters were obtained to determine the upper critical temperature (UCT) in Iberian pigs. After an adaptation period at 28 °C, eight barrows (99 kg) were individually moved to two respirometry chambers and fed ad libitum (standard diet). The heat production (HP) and respiratory quotient (RQ) were measured over 24 h and some physiological parameters were measured every two days at 24, 26, 28, 30 and 32 °C. No differences ( > 0.05) were found in the heart rate (HR; 97.7 beats/min) and rectal temperature (RT; 39.7 °C) between ambient temperatures. Breathing rate (BR) and skin temperature (ST) increased (272 and 2.4%, respectively; < 0.05) along with the temperature; whereas voluntary feed intake (VFI), retained energy (RE) and respiratory quotient (RQ) decreased (40.3, 65.8 and 10.5%, respectively; < 0.001). Overall, HP slightly decreased (19.2%; < 0.01) when the temperature increased. The reduction in RE when the temperature increased was related more to the decrease in VFI rather than to the concomitant reduction in HP. The UCT can be established at 28 for BR, 30 for VFI and RE, and 32 °C for ST, HP and RQ. Overall, the UCT was stablished at 28-30 °C, indicating the good adaptation of Iberian pigs to heat.