Ovulation synchronization and fixed-time artificial insemination in bison using washed frozen sperm

The objective of the study was to improve assisted reproductive technologies needed to establish and deploy a bison genome biobank. In Experiment 1, ovulation was synchronized with either estradiol + progesterone (n=16) or a high-dose of GnRH (n=17), and bison were inseminated with sperm washed using a density gradient centrifugation (DGC) procedure with trypsin before cryopreservation. No difference was found in ovulation rate (combined, 85%) or interval from ovulation-inducing treatment to ovulation (1.3±0.1 days) between groups, but pregnancy rates were unexpectedly low (3/28). In Experiment 2, the fertilizing capacity of DGC trypsin-washed versus unwashed sperm was tested by FTAI after synchronizing female bison using the GnRH protocol. Again, pregnancy rates were low (0/14 using DGC trypsin-washed sperm and 4/17 using unwashed sperm). In Experiment 3, the efficacy of two ovarian synchronization protocols was compared (high-dose GnRH vs hCG). Ovulation rates and synchrony were satisfactory and not different between groups (combined, 75% in 1.5±0.1 days). The DGC washing procedure without trypsin increased the proportion of sperm with normal morphology and decreased the proportion with DNA fragmentation (P