White Leghorn hens were artificially inseminated twice weekly with undiluted semen or semen diluted (1:3) in Tris buffer, pH 6.8 or saline solution (9 g NaCl/l); with or without pre-insemination douching of the vagina with a solution of ampicillin. 2. Pre-insemination douching reduced the bacterial load of the vagina, resulting in an improvement in fertility and hatchability, with a proportionate reduction in the embryonic mortality. 3. The fertilising and hatching abilities of saline-diluted semen were comparable with those of undiluted semen. 4. Dilution of semen with Tris buffer significantly reduced fertility, but not hatchability.
