Comparison of Two Semen Extenders for Cryopreservation of Bighorn Sheep (Ovis canadensis canadensis) Epididymal Sperm

There is a growing amount of interest in the ability to preserve genetics of wildlife and endangered species, such as bighorn sheep (BH). Cauda epididymal sperm preservation is commonly used to salvage genetics from dead or terminally sick males. We have used the technique successfully with a commercial ovine extender1 but this product is no longer available. The objective of this study was to compare the post-thaw quality of BH epididymal sperm using two semen extenders. Post-thaw evaluation included progressive motility, membrane integrity (using the hypoosmotic swelling test (HOST)) and acrosome integrity (using Spermac® stain).
Five bighorn rams aged 1-3 years were castrated using a closed technique. Anesthesia was achieved with an IM injection of Telazol® 5 mL (50 mg tiletamine and 50 mg zolazepam, Zoetis, Flrham Park, NJ) reconstituted with 250 mg (2.5 mL) xylazine and 2.5 mL sterile water and dosed at 4.4 mg/kg Telazol® and 2.2 mg/kg xylazine. The duration of anesthesia was approximately 30 minutes after which tolazoline was administered as a reversal agent. Epididymides were dissected from the testes within three hours of castration, and spermatozoa collected by the float-up technique.1 Left and right epididymides were randomly assigned to be frozen in either the commercial bovine extender Triladyl® (Minitube of America, Verona, WI) or INRA96® (IMV Technology, St Paul, MN) with added 20% egg yolk and 5% glycerol. Two yearling rams were removed from the study because of poor initial semen quality. Recovered sperm was further diluted to a concentration of 200 million/mL and frozen as previously described.1 Straws were thawed at 37°C for 30 seconds prior to evaluation in triplicate. Results of postthaw quality are shown in the table below.  […]