Quantitative aspects of sperm:egg interaction in chickens and turkeys

Spermatozoa embedded in the outer perivitelline layer and points of hydrolysis (holes) produced by spermatozoa in the inner perivitelline layer of chicken and turkey eggs were found to be evenly distributed and linearly correlated (r = 0.80 for both species) throughout the layers from most regions of the egg, except from those directly over the germinal disc, in which there were more holes. In turkey eggs there appeared to be relatively fewer perivitelline spermatozoa, since many had degenerated beyond recognition. In eggs from both species, there were approximately 25 times more holes mm-2 in the inner perivitelline layer from over the germinal disc region than that from other regions of the egg. The relationship between these two frequencies could also be described as linear (r = 0.81 for chicken and 0.78 for turkey eggs), although there was some evidence for a saturation effect for holes over the germinal disc. The fertile status of eggs was shown to be a function of all of the above parameters. Eggs from both species had a 50% probability of being fertile when around 3 spermatozoa penetrated the inner perivitelline layer over the germinal disc and showed maximum fertility when more than 6 spermatozoa penetrated this region. Spermatozoa in the outer perivitelline layer and holes in the inner perivitelline layer from regions other than over the germinal disc could also be used to predict fertility, although with less certainty. Since the number of spermatozoa interacting with the egg reflects the numbers of those stored in the uterovaginal sperm storage tubules, the relationships derived in this work should be useful for understanding how fertility in chickens and turkeys is a function of oviducal sperm storage and transport.