Detecting sperm on the perivitelline membrane of incubated turkey eggs andits implications for research on fertility problems in endangered species

A method whereby sperm nuclei on the perivitelline membrane are stained and counted under a photomicroscope has been used extensively in the poultry i ndustry to show a correlation between egg infertility and low numbers of sp ermatozoa near the site of fertilisation. It has been suggested that this m ethod could also be potentially useful for assessing infertility problems i n endangered species. For poultry, the staining technique is normally appli ed to fresh (i.e. unincubated) eggs, but conservation managers normally col lect eggs for examination only after they have been incubated for several d ays and then assessed (by candling) to lack a developing embryo. Whether sp erm would persist on the perivitelline membrane of infertile eggs incubated over several days is not known. In relation to our research on egg inferti lity in the endangered takahe (Porphyrio hochstetteri), we examined the abo ve problem by comparing sperm counts on the membrane of fresh versus incuba ted infertile eggs from artificially inseminated domestic turkey (Meleagris gallopavo). We were able to detect sperm in most infertile eggs that had n ot 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 cau se the sperm on the membrane to degrade. The inherent fragility of avian sp erm nuclei may limit the usefulness of this technique for assessing inferti lity in takahe and other species where failed (non-developing) eggs are not removed from the nest until after a short period of incubation.