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Abstract
It has been demonstrated that female birds allocate hormones to eggs to enhance offspring quality, but the hormone content of semen contributed by males has received less attention. We measured the concentrations of steroid hormones in seminal and blood plasma from White Leghorn roosters. Progesterone was the most abundant hormone in seminal plasma. To determine the effect of progesterone on fertility, we inseminated hens with semen supplemented with either a high physiological dose of progesterone or a control vehicle, and evaluated fertility using a perivitelline sperm penetration assay. Progesterone inhibited sperm penetration. We then explored how progesterone related to semen quality to pinpoint where progesterone exerts an effect. Progesterone concentrations in circulation and seminal plasma were inversely related to sperm mobility, indicating that males producing more progesterone have poorer quality sperm. These results suggest that steroid hormones exist in avian seminal plasma and may influence sperm performance.