Changes in egg production rate induced by progesterone injection in broiler breeder hens

A polycystic ovarian follicle (PCOF) syndrome associated with high baseline concentrations of progesterone (P4) without preovulatory luteinizing hormone (LH) surges has been reported in turkey hens. The PCOF syndrome could be induced in turkey hens by injecting P4 (0.33 mg/kg per d) daily early in the reproductive period for 10 to 12 d and then waiting 3 wk for the syndrome to develop. It was hypothesized that an arrest in laying associated with the PCOF syndrome could be induced by daily injection of P4 in restricted-fed broiler breeder hens. Hens were divided into 5 treatment groups and were injected subcutaneously daily with P4 in canola oil at dosages of 0, 0.17, 0.33, 0.5, and 1.5 mg/kg per d for 13 d, at 14 wk of egg production when they were 41 wk of age. Blood samples were collected on d 7 and 13 immediately before P4 injection. Oviductal and ovarian morphologies were measured at necropsy 1 d after the last P4 injection. Egg production rate was reduced by injection of P4 at dosages < 0.17 mg/kg per d. At dosages of 0.5 and 1.5 mg/kg per d, ovarian hierarchical follicles had regressed. None of the broiler breeder hens had the PCOF syndrome at necropsy, but a high incidence of hens holding hard-shelled uterine eggs for several days was observed. Concentrations of LH decreased with P4 injection at > 0.17 mg/kg per d, and P4 concentrations were increased with P4 injection at > 0.5 mg/kg per d. Estradiol-17beta (E2) concentrations were decreased at all P4 dosages. It was concluded that egg production rate was reduced by daily injection of P4 at dosages > 0.17 mg/kg per d, and egg production ceased and ovarian follicles and the oviduct regressed at dosages > 0.50 mg/kg per d. The PCOF syndrome, however, was not induced in restricted-fed broiler breeder hens by P4 injection.