Relation between stallion sperm binding to homologous hemizonae and fertility

The hemizona assay (HZA) has been developed as a diagnostic test to predict the fertilisation potential of human spermatozoa. The aim of this study was to develop an HZA for stallion spermatozoa and to investigate a possible relationship between fertility and the outcome of the HZA in this species. Equine oocytes were obtained from ovaries collected at a slaughterhouse and by transvaginal, ultrasound-guided follicle aspiration. They were then denuded from cumulus cells and stored in salt solution at 4 degrees C until use. On the day of the experiments the oocytes were bisected, thus providing 2 equal matching hemizonae from each oocyte. Semen samples from Dutch Warmblood stallions with known fertility data were used to assess the number of spermatozoa bound to the outer side of the hemizona after incubation in vitro. Sperm binding to matching hemizonae of a particular stallion was similar and confirmed the feasibility of using the HZA for the horse. Sperm hemizona binding capacity of 10 pairs of stallions was compared by incubating 1 hemizona with the semen of a stallion and the matching hemizona with the semen of another stallion from the same stud farm. Five matching pairs of hemizonae were used for each pair of stallions. There was a significant relationship between the mean number of spermatozoa bound to matching hemizonae and the fertility indices of stallions from each stud farm (P < 0.0001). It is concluded that HZA can be used as a valuable parameter in stallion semen analysis.