DOES FEED RESTRICTION MIMIC THE EFFECTS OF INCREASED AMBIENT-TEMPERATURE IN LACTATING SOWS

We evaluated the effects of high ambient temperature and feed restrict ion in primiparous lactating sows. Females were exposed to either a co nstant thermoneutral (20 degrees C) or hot environment (30 degrees C). Lactating sows at 30 degrees C were given free access to feed (30AL; n = 12), and sows at 20 degrees C were restricted according to the fee d intake recorded at 30 degrees C (20RF; n = 6) or were given free acc ess to feed (20AL; n = 6). Jugular vein catheters were surgically inse rted at 100 +/- 1 d postcoitum. During lactation, 30AL sows exhibited higher rectal temperatures (P < .05) than 20AL and 20RF sows. Feed int ake was reduced by 43% for 30AL compared with 20AL sows. Daily body we ight loss was lower (P < .05) in the 30AL than in the 20RF group, and mean litter daily gain over the whole lactation was 18% lower in 30AL than in 20AL, sows (P < .05) and was intermediate in 20RF females. Pla sma concentrations of thyroid hormones (triiodothyronine [T-3] and thy roxine [T-4]) were lower at 30 degrees C than at 20 degrees C at d 4 p ostpartum and d 8 after weaning for T-4 (P < .001) and at d 4 postpart um (P < .001) and at d I and d 8 after weaning for T-3 (P < .01) but w ere not influenced by feed restriction at 20 degrees C. Mean concentra tions of cortisol measured on d 4 and 19 postpartum and on d 1 after w eaning were lower in the 30AL than in the 20AL group (P < .05), and ne ither was different from that in 20RF sows. Ambient temperature and fe ed intake had no influence on prolactin concentrations on d 19 postpar tum and d 1 after weaning. In the 30AL group, concentrations of T-3, c ortisol, and prolactin measured at d 19 postpartum were positively cor related with the litter gain observed during the 2nd and 3rd wk of lac tation (P < .05). The return to estrus was slightly delayed in 20RF co mpared with 20AL sows (P < .05) and was quite variable in the 30AL gro up. These results demonstrate that high ambient temperature has negati ve consequences on litter growth and return to estrus and induces plas ma hormonal variations, that cannot be fully mimicked by feed restrict ion in primiparous sows.