Preincubation with green tea polyphenol extract is beneficial for attenuating sperm injury caused by freezing‐thawing in swine

Polyphenols ( PFs ) extracted from green tea, known to be potent anti‐oxidants, have been reported to be effective in increasing the motility and viability of mammalian sperm, preserved in a liquid form. Therefore, we tested whether PFs might also be effective for maintaining the integrity of frozen‐thawed boar spermatozoa. Ejaculates, collected from Clawn miniature pigs, were diluted in a semen extender containing various amounts of PFs (0, 0.01, 0.05, 0.1 and 0.2% w/v) and then stored at 15°C overnight. The semen samples were processed, using the straw freezing procedure, and then frozen in liquid nitrogen. After rapid thawing at 40°C, the spermatozoa were subjected to several assays to evaluate semen quality. Spermatozoa frozen in a medium containing 0.01% w/v PFs exhibited significantly ( P  < 0.05) higher degrees of post‐thawed viability and acrosomal integrity than those stored in the absence of PFs . However, no change in the mitochondrial activity was noted between the two groups. The inclusion of 0.01% PFs in the semen extender was significantly ( P  < 0.05) effective in increasing both the rates of monospermic oocyte formation and of blastocyst formation. These findings indicate that preincubation with the semen extender, containing 0.01% PFs prior to freezing, exerts a protective effect on boar sperm by preventing injuries associated with freezing‐thawing.