Effect of high temperature on feeding behaviour and heat production in group-housed young pigs.

To assess the acclimation of pigs to heat stress, the effects of high (33 degrees C) or thermoneutral (23 degrees C) constant temperatures on feeding behaviour and components of energy balance were studied in group-housed young pigs. Three groups of five pigs were used at each temperature. After 1 week of adaptation, voluntary feed intake (VFI) and heat production (HP) were recorded for thirteen consecutive days. Animals were fed ad libitum. Fasting HP was measured on the last day. Average initial body weights (BW) were 21.4 and 20.9 kg at 23 and 33 degrees C respectively. Feeding behaviour was measured individually and rate of feed intake and characteristics of feeding behaviour were calculated. The O(2) consumption, CO(2) production and physical activity of the group were used to calculate total HP (HP(tot)) and its components, i.e. fasting HP (HP(fas)), HP due to physical activity (HP(act)) and thermic effect of feed (TEF). The BW gain and VFI were reduced by 37 and 30 % respectively at 33 degrees C. The decrease in VFI corresponded to reduced consumption time (-34 %) and size of the meals (-32 %). Feeding behaviour was mostly diurnal (66 % of the VFI), and the rate of feed intake (28 g/min) was not affected by temperature. Daily HP(tot), HP(fas) and TEF, expressed per kg metabolic weight (BW(0.60)), were significantly decreased at 33 degrees C by 22, 18 and 35 % respectively, whereas HP(act) was not affected; TEF expressed per g feed was not affected (2 kJ/g). The decrease in HP(tot) at 33 degrees C was caused by a reduction in TEF and HP(fas) (kJ/d per/kg BW(0.60)), which are both related to reduction in VFI.