Influence of catalase and pre-freezing equilibration on post-thaw semen quality and conception rate in ewes laparoscopically inseminated

Abstract

The aim of this study was to investigate the effects of catalase and pre-freezing equilibration during ram sperm cryopreservation on motility and membrane and acrosomal integrity of frozen-thawed semen, as well as conception rate following laparoscopic timed-insemination. Semen was collected from four mature Dorper rams, pooled and diluted in Tris egg-yolk extender basic solution (CON), or this solution supplemented with catalase (CAT; 20 U/100 × 106 sperm). Extended semen was packaged in 0.25 ml mini straws (25 × 106 sperm/straw), chilled (to 5°C), and then either frozen immediately (CON and CAT) or maintained at 5°C for 12 h of pre-freezing equilibration (CON12 and CAT12). Immediately after thawing and at 1 h after incubation at 37°C, kinematic parameters (CASA), plasma membrane integrity (PI-FITC), and acrosomal status (FITC-PNA) of sperm were assessed. There were no significant differences among the four groups on sperm traits evaluated immediately post-thaw. However, after 1 h of incubation, total motility (46.7 and 25.0%) and plasma membrane integrity (38.7 and 25.7%) were higher (P < 0.05) in CAT12 than CON. When these two treatments were used for laparoscopic timed artificial insemination of ewes (with synchronized ovulation), conception rate was similar for CAT12 and CON (32.8%, n = 61 vs. 27.3%, n = 55). In conclusion, the combination of catalase and pre-freezing equilibration resulted in significantly improved quality of post-thawed ram semen without affecting conception rate in fixed-time laparoscopically intrauterine inseminated ewes.