Abstract
In photostimulated red‐winged blackbirds (Agelaius phoeniceus) receiving intermittent injections of 10.0 μg of a potent GnRH analogue (GnRH‐A), the pituitary gland was not desensitized, the androgen response was not clearly impaired, and the diameter of the seminiferous tubules was not modified in GnRH‐A‐treated birds compared to saline‐injected redwings. However, the thickness of the germinal epithelium was significantly reduced in redwings receiving 10.0 μg of GnRH‐A every 4th day and every 7th day compared to the saline‐injected redwings. Surprisingly, the group receiving the maximum number of injections (treated every 2nd day) had a thickness of the germinal epithelium and a proportion of individuals with normal spermatogenesis similar to the saline‐injected group and other GnRH‐A‐treated groups. The proportion of redwings with disturbed spermatogenesis was significantly higher in groups receiving GnRH‐A every 4th day and every 7th day compared to saline‐injected redwings. Impairment of spermatogenesis in redwings treated with GnRH‐A at different frequencies occurred without pituitary desensitization and the clear failure of the androgen response, suggesting that factors affecting Sertoli cell and Leydig cell function are involved.