Development of an optimal protocol to induce capacitation of boar spermatozoa in vitro

In 1951, Colin Russell Austin and Min Chueh Chang identified "capacitation", a special process involving ejaculated spermatozoa in the female reproductive tract. Capacitation is a phenomenon that occurs in vivo, but almost all knowledge of capacitation has been obtained from in vitro studies. Therefore, numerous trials have been performed to establish in vitro capacitation methods for various studies on reproduction. Although a series of studies have been conducted to develop an optimal protocol for inducing capacitation, most have focused on identifying the appropriate chemical compounds to induce the capacitation of boar spermatozoa in vitro. Therefore, the purpose of this study was to identify the optimal incubation time for inducing capacitation in vitro. Duroc semen was incubated for various periods (60, 90, and 120 min) to induce capacitation. Sperm function (sperm motility, motion kinematic parameters, and capacitation status) was evaluated. The results showed that total sperm motility, rapid sperm motility, progressive sperm motility, curvilinear velocity, and average path velocity significantly decreased in a time-dependent manner. However, the capacitation status did not show any significant changes. Taken together, these results indicate that an incubation time of more than 60 min suppresses sperm motility and motion kinematic parameters. Therefore, we suggest that 60 min may be the best incubation time to induce capacitation without negative effects on sperm motility and motion kinematics in boar spermatozoa in vitro.