EVALUATION OF RELATIVE FERTILITY OF CRYOPRESERVED GOAT SPERM

This study was designed to compare differences in the in vivo fertilit y of cryopreserved goat semen assessed by heterospermic insemination w ith differences in in vitro analyses. Five groups of does were insemin ated with mixed frozen-thawed semen from different pairs of bucks. The percentage of offspring sired by each buck in the pair was compared w ith the relative ability of spermatozoa from that frozen-thawed ejacul ate to penetrate zona-free hamster ova, relative post-thaw acrosomal i ntegrity, ability to undergo an acrosome reaction during in vitro capa citation, and assessments of sperm motility. In 4 of the 5 different i nsemination pairs, the ratio of offspring born was other than 1:1. Acr osomal integrity, ability of spermatozoa to undergo an acrosome reacti on, and parameters of sperm motility were not correlated with differen ces in relative fertility in this experiment using ejaculates from fer tile bucks. The ability of spermatozoa to fuse with the oocyte plasma membrane was highly correlated with relative in vivo fertility (R(2) = 0.78, P = 0.04). This suggests that fusion with the oocyte plasma mem brane is an event in the fertilization process in which significant va riation exists among fertile bucks. Assessment of ability of spermatoz oa to fuse with zona-free hamster ova may contribute to analysis of po st-thaw fertility of frozen-thawed buck semen.