Influence of high ambient temperature on performance of reproductive sows

Two trials were conducted on pure Large White multiparous (Trial 1, n = 36) and primiparous (Trial 2, n = 24) sows exposed to an ambient temperature within the zone of thermal comfort (18 or 20 degrees C) or above the evaporative critical temperature (27 or 30 degrees C). During a 3-week lactation, all sows in Trial 1 and those maintained at 30 degrees C in Trial 2 were fed ad libitum whereas sows at 20 degrees C in Trial 2 were paired-fed with those at 30 degrees C. The same standard diet containing 17.2% crude protein, 0.84% lysine and 13.0 MJ DE/kg was used during lactation. Single blood samples were drawn from the jugular vein before the morning meal at day 107 of gestation, at days 13 and 20 post-partum (p.p.), at days 1 and 12 post-weaning in Trial 2. After weaning, sows were checked daily for oestrus in the presence of a mature boar. Daily feed intake was lower at 27 degrees C than at 18 degrees C from day 4 p.p. until weaning in Trial 1 (-28%) and very low in both groups of sows in Trial 2 (2.8 kg/day). Lactational loss of sow Liveweight did not differ between groups in Trial 1 whereas it was lower at 30 degrees C than at 20 degrees C in Trial 2 (1.32 vs. 1.80 kg/day, P < 0.001). Daily litter growth was lower in the warmer environment in both trials (Trial 1: 1.58 vs. 2.15 kg/day, Trial 2: 1.60 vs. 1.95 kg/day, P < 0.05). In Trial 2, plasma concentrations of thyroid hormones were lower at 30 degrees C than at 20 degrees C (T3: 0.51 vs. 0.61 ng/ml; T4: 22.5 vs. 28.5 ng/ml), those of free fatty acids and insulin-like growth factor-I did not differ between treatments and, glycemia was higher at 30 degrees C (P < 0.05). The weaning-to-oestrus interval was longer at 27 degrees C than at 18 degrees C in Trial 1 but did not differ between temperatures in Trial 2, being delayed in both environments. In conclusion, high ambient temperature reduces appetite, milk production and body reserve mobilization of sows in order to limit heat production. Reduction in feed intake plays probably a role in the delayed return-to-oestrus after weaning under elevated temperature. (C) 1997 Elsevier Science B.V.