The xenogenous capacitation response of fresh, cooled/extended and frozen/thawed equine semen as determined by a chlortetracycline stain

Twenty-three crossbred ewes were utilized during 1995, to investigate the possibility of xenogenous capacitation, using stallion spermatozoa. Ewes were grouped according to endocrine status as anestrus (n = 12) or estrus (n = 11) and were surgically inseminated with either fresh (FR), cooled/extended (FCE) or frozen/thawed (FZ) spermatozoal samples. The capacitation response of spermatozoa recovered from oviductal flushing 4 - 6 hours post-insemination, was assessed using a chlortetracycline (CTC) fluorescent probe.

Data were recorded as percentages of spermatozoa exhibiting CTC staining patterns characteristic of capacitated (PCAP), unreacted (PUR) and acrosome reacted (PAR) sperm. Mean PCAP was not significantly different in estrous ewes despite an increasing trend. Mean PUR and PAR were also not different.

Differences in capacitated, acrosome reacted and unreacted spermatozoa in inseminated and recovered samples (CAPDIF, ARDIF and URDIF, respectively) were analyzed. CAPDIF was significantly different between treatment groups (p < 0.01). CAPDIF was also significantly greater for the estrus versus anestrus group (p < 0.05).

Total number of spermatozoa recovered (RTOTAL) was recorded. More spermatozoa were recovered from estrus ewes, however significance was not established. Mean number of spermatozoa recovered was 37.9 ± 35.9 per ewe. Treatment significantly affected RTOTAL in estrus animals (p = 0.01). FR samples had the highest recovery.

Results suggest that xenogenous capacitation of stallion semen may occur in the reproductive tract of the ewe. Implications of these results are discussed in regards to their application of xenogenous gamete intrafallopian transfer (X-GIFT) as a treatment option for certain infertility problems in the mare.