ENDOCRINE CHANGES IN SOWS EXPOSED TO ELEVATED AMBIENT-TEMPERATURE DURING LACTATION

Seven sows were placed into one of two environmental chambers at 22 C, 5 d prior to farrowing. On day 9 of lactation, one chamber was changed to 30 C (n = 4) and the other remained at 22 C (n = 3). On days 24 and 25, blood samples were collected every 15 min for 9 hr and 7 hr, respectively. On day 24, thyrotropin releasing hormone (TRH) and gonadotropin releasing hormone (GnRH) were injected iv at hour 8. On day 25 naloxone (NAL) was administered iv at hour 4 followed 2 hr later by iv injection of TRH and GnRH. Milk yield and litter weights were similar but backfat thickness (BF) was greater in 22 C sows (P < .05) compared to 30 C sows. Luteinizing hormone (LH) pulse frequency was greater (P < .003) and LH pulse amplitude was less (P < .03) in 22 C sows. LH concentrations after GnRH were similar on day 24 but on day 25, LH concentrations after GnRH were greater (P < .05) for 30 C sows. Prolactin (PRL) concentrations were similar on days 24 and 25 for both groups. However, PRL response to TRH was greater (P < .05) on both days 24 and 25 in 30 C sows. Growth hormone (GH) concentrations, and the GH response to TRH, were greater (P < .0001) in 30 C sows. Cortisol concentrations, and the response to NAL, were less (P < .03) in 30 C sows. NAL failed to alter LH secretion but decreased (P < .05) PRL secretion in both groups of sows. However, GH response to NAL was greater (P < .05) in 30 C sows. Therefore, sows exposed to elevated ambient temperature during lactation exhibited altered endocrine function.