EFFECT OF EXOGENOUS PROGESTERONE ON LUTEINIZING-HORMONE SECRETION IN DOMESTIC TURKEY HENS AT DIFFERENT REPRODUCTIVE STATES

To determine effects of progesterone (P4) treatment on luteinizing hor mone (LH) secretion in turkey hens, two trials were conducted. Trial 1 was to determine changes in LH, P4, and testosterone (T) during photo stimulation. Photosensitive turkey hens were maintained under short da ys (SD) of 6 h light and 18 h dark. At the beginning of Trial 1, blood samples were taken daily for 4 days, then one-half of the hens were s witched to long days (LD) of 14 h light and 10 h dark, and daily blood samples were continued until 5 days after eggs were laid by all the h ens switched to LD. Concentrations of LH, PI, and T increased signific antly 1 day after switching hens from SD to LD, but the increase in P4 was initially low with a further increase occurring by 3 days prior t o first eggs. In Trial 2, turkey hens were injected with exogenous P4 to determine if P4 is an initiator of the preovulatory surge of LH. P4 or vehicle were injected im in hens at three different reproductive s tates: (1) while hens were maintained under SD, (2) on the 5th day aft er hens were switched from SD to LD, and (3) after hens were laying fo r 1 week. The hens were serially bled at 10-min intervals for 8 h to m onitor changes in LH and P4. After 2 h of serial bleeding, P4 or vehic le was injected and bleeding was continued for an additional 6 h. Afte r P4 injection, its concentration increased rapidly from a base level of 0.25-1.20 ng/ml to a postinjection high level of 4.42-6.10 ng/ml wi thin 20 min. The high level of P4 was then maintained throughout the r emaining 6 h. No increases of LH secretion were observed after P4 or v ehicle injection in hens at either State 1 or State 2. Small increases of LH secretion were detected about 2 h after P4 injection in hens at State 3, but these increases were not significantly above vehicle-inj ected controls. Thus, there was no positive feedback effect of P4 inje ction on LH secretion in this trial. These results suggest that P4 mig ht not induce LH secretion in immature or mature turkey hens and might not be the factor which induces the preovulatory surge of LH in layin g turkey hens. Nonsteroidal factors of ovarian origin might be involve d in regulating the preovulatory surge of LH in turkey hens. (C) 1998 Academic Press.