Author
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Proudman, John |
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Submitted to: Journal Of Poultry Science
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 9/22/1997 Publication Date: N/A Citation: N/A Interpretive Summary: Prolactin (PRL), produced by the pituitary gland, causes incubation behavior and ovarian regression in turkey hens and decreases hatching-egg production. PRL secretion changes greatly during the reproductive cycle, such that plasma PRL concentrations vary up to 100-fold and are diagnostic of the reproductive state of the hen. Previous work has shown that plasma PRL levels vary with the light-dark cycle, and that PRL concentration increases dramatically as the hen ceases laying and begins incubating. This study was conducted to determine if nightime PRL levels may rise before daytime PRL levels in hens which are beginning to incubate, and thus provide an early identification of hens that are about to cease laying. Results showed that circulating PRL levels increased greatly with the onset of incubation behavior, but night and daytime PRL levels changed in parallel. Hens which laid eggs at a high rate had moderate PRL levels throughout egg production. PRL levels did not differ among laying hens with high or low nesting frequency. Plasma PRL levels declined to low levels in hens which ceased laying. The results demonstrate that daytime PRL measurements accurately reflect reproductive state, and that moderate PRL levels seem optimum for best egg production. These findings will be used by scientists to better understand how changing PRL levels may influence reproduction. Technical Abstract: Plasma prolactin (PRL) levels rise following long daily photostimulation, and increase dramatically at the onset of incubation behavior. Previous work has shown that a daily rhythm in PRL secretion may occur, with the lowest PRL levels found prior to lights out and the highest levels found prior to lights on. It has been suggested that an early event in the onset tof incubation behavior may be an increase in nocturnal PRL secretion. A retrospective study was conducted to contrast the morning and evening PRL secretion patterns at weekly intervals throughout the reproductive cycle in birds which exhibited: 1) incubation behavior; 2) high egg production and low nesting frequency for the last 16 wk of a 21-wk reproductive cycle; 3) high egg production while nesting frequently; or 4) photorefractoriness (defined by a cessation of egg production without incubation behavior). All hens showed an increase in PRL levels following photostimulation. Over r50% of the hens studied had significantly higher PRL levels at the end of the scotophase than at the end of the photophase. Circulating PRL levels increased greatly with the onset of incubation behavior, but morning and evening PRL levels changed in parallel. Good layers had moderate PRL levels throughout egg production, but PRL levels did not differ among laying hens with high or low nesting frequency. Plasma PRL levels declined to low levels in photorefractory hens. These results show that daytime PRL measurements accurately reflect reproductive state, and that moderate PRL levels seem optimum for best egg production. |
