EFFECT OF LONG-TIME EXPOSURE TO DIFFERENT ENVIRONMENTAL TEMPERATURES ON HEAT-PRODUCTION OF GROWING PIGS

The objective of the experiments was to investigate the influence of t he duration of exposure to different environmental temperatures on the heat production (HP) of growing pigs. 5 trials were carried out with Landrace castrated male pigs at temperatures of 6, 12, 18, 24 and 30 d egrees C. Each trial lasted 9 weeks and four animals with an initial l ive weight (LW) of 47 +/- 2.5 kg were involved. The animals were house d individually. The diet contained 15 MJ ME/kg DM and 19% crude protei n. The feeding level was 2.9-times maintenance energy requirement. HP of the pigs kept at 6 and 12 degrees C was higher than in pigs kept at 18, 24 and 30 degrees C. Over the time of the experiment HP decreased in all cases, but the extent of the decrease was higher at 6 and 12 d egrees C (15 and 17%, respectively). The coefficients of a regression relating daily HP (all values adjusted to a ME intake of 1292 kJ/kg LW (0.75). d) to time (week) were: -21.5 (6 degrees C); -20.3 (12 degrees C); -4.2 (18 degrees C); -6.5 (24 degrees C); -5.3 (30 degrees C) kJ/ kg LW(0.75). d . week. It was concluded that over the time of the tria ls a reduction of the thermoregulatory part of the HP takes place. Inv estigations on the morphology of the body core after slaughter showed a marked increase of longer bristles of the pigs kept at 12 degrees C, than in pigs kept at 24 degrees C. The thickness of dorsal fat was al so higher. The results show that an important mechanism of acclimation to a cold environment in pigs is the increasing body insulation which leads to a reduction of energy losses for thermoregulatory responses.