Artificial insemination with seminal plasma improves the reproductive performance of frozen-thawed boar epididymal spermatozoa.

Frozen-thawed epididymal spermatozoa have good fertilization capability in vitro; however, their artificial insemination conception rate is less than half of that of frozen-thawed ejaculated spermatozoa. Because the addition of seminal plasma to the thawing solution enhances the in vivo fertilizing ability of frozen-thawed ejaculated spermatozoa, we hypothesized that the reproductive performance of frozen-thawed epididymal spermatozoa could also be improved by the inclusion of seminal plasma. When frozenthawed epididymal spermatozoa were incubated for up to 6 hours, the motility of the sperm significantly decreased in a time-dependent manner. The acrosomal membrane was damaged in the majority of frozen-thawed epididymal spermatozoa. The addition of seminal plasma to the thawing solution significantly decreased the percentage of sperm with abnormal acrosomes and increased their total motility in a dose-dependent manner. Furthermore, the addition of seminal plasma reduced the abundance of a 15-kDa tyrosinephosphorylated protein in frozen-thawed sperm, and the maximum effect was observed at 15% (vol/vol) seminal plasma. When cryopreserved epididymal spermatozoa from 3 different boars were thawed with a 15% (vol/vol) seminal plasma-containing solution, the conception rate and mean litter size obtained by artificial insemination were significantly increased as compared with those in the control without seminal plasma. From these results, we concluded that the addition of seminal plasma to the thawing solution is a key step in obtaining an optimal number of piglets by artificial insemination using frozen-thawed boar epididymal spermatozoa.