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Chronic prenatal heat stress alters growth, carcass composition, and physiological response of growing pigs subjected to postnatal heat stress.

Postnatal heat stress (HS) effects on pig physiology and performance are widely studied but prenatal HS studies, albeit increasing, are still limited. The objective of this study was to evaluate chronic prenatal HS effects in growing pigs raised in postnatal thermoneutral (TN) or in HS environment. For prenatal environment (PE), mixed-parity pregnant sows were exposed to either TN (PTN; cyclic 18 to 24°C; n = 12) or HS (PHS; cyclic 28 to 34°C; n = 12) conditions from d 9 to 109 of gestation. Two female offspring per sow were selected at 10 weeks of age and allotted to one of two postnatal growing environments (GE):GTN (cyclic 18 to 24°C; n = 24) and GHS (cyclic 28 to 34°C; n = 24). From 75 to 140 d of age, GTN pigs remained in GTN conditions, while GHS pigs were in GTN conditions from 75 to 81 d of age and in GHS conditions from 82 to 140 d of age. Regardless of PE, postnatal HS increased rectal and skin temperatures (+0.30 and +1.61 °C on average, respectively; P < 0.01), and decreased ADFI (-332 g/d; P < 0.01), resulting in lower ADG and final BW (-127 g/d and -7.9 kg, respectively; P < 0.01). The GHS pigs exhibited thicker backfat (P < 0.01), lower carcass loin percentage (P < 0.01), increased plasma creatinine levels (P < 0.01), and decreased plasma glucose, nonesterified fatty acids, T3, and T4 levels (P < 0.05). Prenatal HS increased feed intake in an age-dependent manner (+10 g•kg BW-0.60•d-1 for PHS pigs in the last 2 weeks of the trial; P = 0.02) but did not influence BW gain (P > 0.10). Prenatal HS decreased plasma levels of superoxide dismutase on d 3 of GHS (trend at P = 0.08) and of T4 on d 49 (P < 0.01) but did not affect T3 on d 3 nor 49 (P > 0.10). Prenatal HS increased rectal and skin temperatures, and decreased temperature gradient between rectal and skin temperatures in GTN pigs (+0.10°C, +0.33 and -0.22°C, respectively; P < 0.05) but not in GHS pigs (P > 0.10). There were also PE×GE interactions found with lower BW (P = 0.06) and higher backfat (P < 0.01) and perirenal adiposity (P < 0.05) for GHS-PHS pigs than the other groups. Overall, increased body temperature, and altered thyroid functions and physiological stress responses suggest decreased heat tolerance and dissipation ability of pigs submitted to a whole-gestation chronic prenatal HS. Postnatal HS decreased growth performance, increased carcass adiposity, and affected metabolic traits and thyroid functions especially in pigs previously submitted to prenatal HS.