Plasma Progesterone, Luteinizing Hormone Concentrations, and Granulosa Cell Responsiveness in Heat-Stressed Hens ,

Abstract

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 ≈6 h prior to ovulation. Progesterone levels from HS hens were lower from 6 h [.07 ± .01 (SE) versus 1.66 ± .25 ng/mL; P = .008] to predicted ovulation (.06 ± .006 versus .70 ± .18 ng/mL; P = .07). Likewise, LH levels from HS hens were lower from 6 h (1.55 ± .16 versus 3.86 ± .34 ng/mL; P = .007) to predicted ovulation (1.63 ± .18 versus 2.50 ± .27 ng/mL; P = .01). Eggs from HS hens were more often laid early (< 24 h) than eggs from US hens (71.42 versus 13.33%, respectively, P = .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 = .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 = .001). In contrast, basal progesterone secretion by cells from HS hens was 40.25 ± 6.60 ng/mL (P = .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.