Plasma progesterone, luteinizing hormone concentrations, and granulosa cell responsiveness in heat-stressed hens

Plasma progesterone and luteinizing hormone (LH) profiles were obtained during the first ovulatory cycle of heat-stressed (HS, 35 C; n = 24) and unstressed (US, 17 to 27 C; n = 24) hens using 30-min sampling intervals beginning approximately 6 h prior to ovulation. Progesterone levels from HS hens were lower from 6 h .07 +/- 0.1 (SE) versus 1.66 +/- 0.25 ng/mL; P = 0.008 to predicted ovulation (.06 +/-.006 versus 0.70 +/- 0.18 ng/mL; P = 0.07). Likewise, LH levels from hens were lower from 6 h (1.55 +/- 16 versus 3.86 +/- 0.34 ng/mL; P =.007) to predicted ovulation (1.63 +/- 0.18 versus 2.50 +/- 0.27 ng/mL; P = 0.01). Eggs from HS hens were more often laid early (< 24 h) than eggs from US hens (71.42 versus 13.33%, respectively; P = 0.01), but US hens more often laid eggs of a normal oviposition interval length (24 to 26 h) compared with HS hens (73.34 versus 14.29%; P =.0005). The percentage of delayed eggs (> 26 h) was not different (US, 14.29 versus HS, 13.37%; P = 0.75) between the two treatment groups. Basal production of progesterone by dispersed granulosa cells from US hens was 97.62 +/- 16.01 ng/mL. Challenge by LH increased this to 417.50 +/- 53.38 ng/mL (P = 0.001). In contrast, basal progesterone secretion by cells from HS hens was 40.25 +/- 6.60 ng/mL (P = 0.0001) and LH challenge failed to increase progesterone production. The results indicate possible direct HS effects on ovarian tissue, perhaps in addition to other indirect effects, as a contributing factor to the decline in egg production.