Ovary

Progesterone Injection and Egg Production in Turkey Hens

Abstract
An arrest in laying associated with a poly-ovarian follicle (POF) or polycystic-ovarian follicle (PCOF) syndrome has been reported in turkey hens photostimulated at an early age with a constant light photoperiod. Hens expressing the POF or PCOF syndrome had stopped laying for several weeks (wk), but the ovary contained an increased number of mature size and larger follicles (POF hens), which were cystic (PCOF) in some of the hens. Hens with the POF and PCOF syndromes had plasma progesterone (P₄) concentrations that were relatively high and without surges. We hypothesized high plasma P₄ concentrations may block ovulatory surges of LH but not block the growth or maintenance of hierarchical follicles leading to development of the POF or PCOF syndrome in turkey hens. In the first 6 studies, hens were photostimulated with either a 14 hour (hr) light (L) 10 hr dark (D) (14L:10D) or a 24L:0D photoperiod and after laying for 1 to 38 wk, then injected daily for up to 14 days (d) with P₄ (up to 1.50 mg kg^-1 d^-1), and necropsied. At all ages, oviposition rate was reduced at a P₄ dosage of 0.17 mg kg^-1 d^-1. But with dosages of 0.33 mg kg^-1 d^-1 or greater ovipositions stopped in most hens within about 2 d. For hens laying for less than 15 wk, oviductal weight and number of hierarchical follicles of P₄ injected hens were not different from control vehicle injected hens, but the number of mature, cystic, and atretic follicles were increased. For hens laying for 38 wk when treated with P₄, oviductal weight and number of hierarchical follicles decreased, but number of atretic follicles increased. There was no photoperiod effect on egg production, oviductal weight, or follicle number and none of the hens developed the POF or PCOF syndrome in these experimants. Two additional experiments were conducted with hens early in the reproductive period that had been photostimulated with 14L10D or 24L:0D and injected with P₄ (0.33 mg P4 kg^-1 d^-1) for 10 or 12 d but not necropsied until 3 wk after the last injection. Most of the hens photostimulated with the 24L:0D photoperiod and injected with P₄, and a few of the hens photostimulated with 14L:10D and injected with P₄ had developed the PCOF syndrome when necropsied. The hens with the PCOF syndrome had high levels of P₄ when necropsied. From these studies we concluded that the PCOF syndrome can be induced early in the reproduction period by photostimulating turkey hens with a 24L:0D photoperiod, injecting them for 10 to 12 d with P₄ at a dosage of 0.33 mg kg^-1 d^-1, and then waiting 3 wk for the PCOF syndrome to develop.

Key words: Ovary • Pituitary • Luteinizing hormone • Ovulation • Progesterone