242 EFFECTS OF TWO COMMERCIAL BOVINE SEMEN EXTENDERS FOR SHORT-TERM STORAGE ON MOTILITY PATTERN OF CHILLED BISON SEMEN

Abstract

Difficulties of adequate cryopreservation of bison semen has limited the success of artificial insemination and in-vitro embryo production in bison. We evaluated the effects of short-term cooling on motility of bison sperm using two commercial semen extenders (Triladyl® and Andromed®; Minitube, Ingersoll, ON, Canada). Semen was collected by electroejaculation of mature wood bison (n = 3) and plains bison (n = 3) twice a week for 2 wk. Upon collection, the ejaculate was divided into 3 equal aliquots, which were then diluted 1:2 (vol/vol) in Triladyl or Andromed, or were not extended (n = 24 samples per treatment). Samples were maintained at 37°C until transfer to the laboratory (≤2 h). One millilitre of each sample was then placed into a test tube (15 mL, BD Falcon, BD Biosciences, San Jose, CA, USA) and were kept in water bath set at 5°C inside a walk-in refrigerator (4°C). Characteristics of sperm motility were evaluated before cooling (Day 0) and every 24 h after cooling for 5 days using a computer-assisted semen analyzer. Total motility (TM), progressive motility (PM), velocity curved line (VCL), velocity average path (VAP), and velocity straight line (VSL) were compared among treatments by ANOVA for repeated-measures. Values are expressed as mean ± SEM. After collection, the PM of the raw semen and semen extended in Triladyl or Andromed were not significantly different (63.1 ± 4.4%, 63.3 ± 3.1%, and 56.9 ± 4.5%, respectively). Cooling semen for a period of 24 h resulted in a decrease (P < 0.05) in PM in all 3 groups (4.4 ± 2.0%, 22.7 ± 2.9%, and 28.7 ± 4.3%, respectively). The PM of semen extended in Tryladyl or Andromed was greater than that of raw semen on Day 1 (P < 0.05). Semen extended in Triladyl and Andromed maintained PM on Day 2 (24.7 ± 3.3% and 21.8 ± 3.8%, respectively), but PM declined progressively to 1.1 ± 0.6% and 6.3 ± 2.1% by Day 5. A similar pattern was observed for the TM. The VCL, VAP, and VSL parameters for semen extended with Triladyl and Andromed decreased gradually between Day 0 and Day 5 (P < 0.05). From Day 1 to 4 after cooling, these velocity parameters were not significantly different between semen extended with Triladyl or Andromed; however, they were greater than those of raw semen (P < 0.05). All sperm velocity parameters for the raw semen declined by more than 60% between Days 0 and 2 (P < 0.05). On Day 0, VCL for semen extended with Andromed (152.2 ± 4.3) was greater than that of semen extended with Triladyl and raw semen (P < 0.05; 122.5 ± 7.0 and 122.4 ± 6.6, respectively). The VCL then decreased to 98.9 ± 12.9, 100.5 ± 10.8, and 18.6 ± 6.8 in Andromed, Triladyl and raw groups respectively on Day 2 (P < 0.05), followed by a further decline to 51.8 ± 14.3, 19.9 ± 10.0, and 9.0 ± 5.0, respectively, observed on Day 5. In conclusion, both Triladyl and Andromed improved characteristics of sperm motility of chilled bison semen. Despite an initial decrease within the first 24 h, bison sperm extended with Triladyl or Andromed maintained an acceptable degree of motility for up to 2 days after chilling to 5°C.