Abstract

A method whereby sperm nuclei on the perivitelline membrane are stained and counted under a photomicroscope has been used extensively in the poultry industry to show a correlation between egg infertility and low numbers of spermatozoa near the site of fertilisation. It has been suggested that this method could also be potentially useful for assessing infertility problems in endangered species. For poultry, the staining technique is normally applied to fresh (i.e. unincubated) eggs, but conservation managers normally collect eggs for examination only after they have been incubated for several days and then assessed (by candling) to lack a developing embryo. Whether sperm would persist on the perivitelline membrane of infertile eggs incubated over several days is not known. In relation to our research on egg infertility in the endangered takahe (Porphyrio hochstetteri), we examined the above problem by comparing sperm counts on the membrane of fresh versus incubated infertile eggs from artificially inseminated domestic turkey (Meleagris gallopavo). We were able to detect sperm in most infertile eggs that had not been incubated, but no sperm at all were detected in infertile eggs that were incubated for seven days, suggesting that warming of the eggs may cause the sperm on the membrane to degrade. The inherent fragility of avian sperm nuclei may limit the usefulness of this technique for assessing infertility in takahe and other species where failed (non-developing) eggs are not removed from the nest until after a short period of incubation.