Abstract
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 hardshelled eggs in the uterus. Plasma E2 concentrations were affected both by feeding pattern and P4 injection. Progesterone injection depressed plasma E2 concentration 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.
Highlights
Progesterone is the major hormone secreted by granulosa cells of large mature hierarchical follicles (F1) in birds
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; this higher ovulation rate did not result in more settable egg production
Feed satiated hens have been shown to have more large yellow follicles than their restricted fed counterparts, so the objective of this study was to evaluate the effects of injection of a high dose of P4 to simulate the essential P4 surge required for establishment of LH surge in feedsatiated and feed-restricted broiler breeder hens during post peak production period on egg production, ovulation rate and ovarian morphology
Summary
Progesterone is the major hormone secreted by granulosa cells of large mature hierarchical follicles (F1) in birds. The progesterone production by F1 follicle peaks 6 to 8 h prior to ovulation (Johnson and van rinhoven, 1980) and triggers gonadotropin-releasing hormone (GnRH) release by the hypothalamus. This in turn is followed by an increase in LH and FSH release from the anterior pituitary. Single injection of an acute dose of P4 in laying hens during the preovulatory open period has been shown to have positive effect on inducing a preovulatory LH surge and ovulation (Wilson and Sharp, 1975, 1976; Johnson et al, 1985)
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