Effect of high temperature and feeding level on energy utilization in piglets

The effect of temperature (23 or 33 degreesC) and feeding level on componen ts of energy balance was studied in seven groups of individually reared Pie train x (Landrace x Large White) littermate piglets. Within each litter, on e pig was reared at 23 degreesC and given a predefined feeding level close to ad libitum (23AL pigs), one was reared at 33 degreesC and also fed close to ad libitum (33AL), and one was reared at 23 degreesC and pair-fed to th e 33AL pig (23PF). Piglets of one litter were acclimated during 2 to 4 wk t o their experimental temperature in temperature-controlled rooms before bei ng transferred tone per week) to a respiration chamber for measurement of n itrogen and energy balances. The average initial BW was 22.4 kg. The data o n O-2 consumption, CO2 production, and physical activity were collected ove r seven consecutive days and used to calculate total heat production (HPtot and its components: fasting heat production (FHP), heat production due to physical activity (HPact), and thermic effect of feed (TEF). A preliminary trial was conducted in which heat production was measured in three piglets according to a Latin square design at 23, 25, and 27 degreesC. Total heat p roduction was, but activity-free heat production was not, affected by tempe rature, and no firm conclusions could be drawn as to whether 23 degreesC wa s within the thermoneutral zone of fed piglets. In Trial 2, the combination of increased temperature and reduced feed intake resulted in a 20% lesser heat production in 33AL than in 23AL pigs. This was due to a reduction in b oth TEF (-39%) and FHP (0.642 vs 0.808 MJ(.)d(-1.)kg BW-0.60). Despite the shorter duration of standing activity, HPact was slightly higher at 33 degr eesC, probably due to hyperventilation at this temperature. With similar fe eding levels (23PF vs 33AL), HPtot and activity-free heat production were l ess at 33 degreesC and energy retention as protein (+6%) and fat (+31%) was increased. Because HPact was similar for both treatments, the greater ener gy retention for 33AL seemed to be due to a greater utilization of feed ene rgy or to a reduced maintenance requirement (i.e., reduced FHP). However, t he type of stress imposed on 23PF and 33AL pigs was different and may have affected energy metabolism. The results suggest that the reduction in heat production of piglets at high ambient temperatures is caused by a reduction in voluntary feed intake and differences in energetic efficiency. The mech anisms for the lesser efficiency at 23 degreesC compared to 33 degreesC (at the same level of feed intake) remain unclear.