An experiment was conducted to evaluate responses of feed-satiated and feed- restricted breeder hens to daily injection of progesterone (P4). A total of 64 Cobb 500 hens were fed either restricted or ad libitum from 27 to 38 wk of age. Fourteen laying hens from each group were selected to conduct P4 injection assay. Half of birds in each group (n = 7) were injected daily by 2.5 mg P4/kg BW and remaining birds were used as control. The P4 was injected subcutaneously, at the base of the neck daily (at 0900 h) for 21 d. Settable and abnormal eggs were recorded daily. Blood samples were taken just before initiation of injections, 10-d and 20-d after initiation of injection. Plasma samples were analyzed for glucose, cholesterol, triacylglycerol (TAG), P4, estradiol (E2), testosterone, T3 and T4 concentration. Settable egg production declined following P4 injection, whereas total egg production (including soft shell egg) remain at high levels in injected birds during the first week after initiation of P4 injection. Progesterone injection in feed-satiated and feed-restricted birds resulted in ovary regression; the ovary of these birds had no hierarchical follicle. Progesterone injection increased incidence of holding hard-shelled eggs in the uterus. Plasma E2 concentrations were affected both by feeding pattern and P4 injection. Progesterone injection depressed plasma E2concentration in both ad libitum and restricted fed hens. Hens with free access to feed had significantly lower plasma E2 levels compared to restricted fed hens. Our results revealed that whereas injection of P4 induced frequent ovulation early in the injection period in both feed- satiated and feed-restricted breeder hens; however this higher ovulation rate did not result in more settable egg production.
Key words: Progesterone, ad libitum, broiler breeder.
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