Detection of the effects of ingested caffeine on fertility of cocks by homospermic and heterospermic insemination.

Cocks were fed diets containing 0, 0.025, 0.05, 0.075 or 0.1% caffeine during a 14-day treatment period. The number of spermatozoa produced by cocks fed 0.075 or 0.1% caffeine declined sharply at 12 days after onset of treatment. Hens were inseminated with a constant number of spermatozoa from individual cocks. The fertility of cocks fed 0.05, 0.075 or 0.1% caffeine declined during the 17-day post-treatment period and then returned to pretreatment levels. Cocks whose offspring were distinguishable were paired and relative fertility was assessed in a heterospermic test. One cock in each pair was fed 0.05% caffeine during the treatment period. Hens were inseminated with semen mixed within pairs. The proportion of chicks sired by cocks fed caffeine decreased during treatment and remined at that level until 17 days after treatment, when it increased to pretreatment levels. The percentage of total eggs hatched declined concomitantly with the reduction in the proportions of chicks sired by treated cocks. These results indicate that the effect of low levels of a toxin could be detected by reduced numbers of eggs hatched after heterospermic insemination with semen of normal appearance.