Effects of different semen extenders on sperm motility and pregnancy rates in donkeys

Semen quality is highly associated with the success of artificial insemination (AI). The characteristics of semen preserved at room temperature will be influenced by various factors. The semen extender provides sufficient energy for sperm, maintains pH and osmotic pressure stability, inhibits the reproduction of microorganisms and thus prolongs the survival time of sperm. We investigated effects of extender type on semen motility and pregnancy rates in donkeys. Five Yangyuan jacks and 1000 Yangyuan jennies were included in the study. Semen was collected by artificial vagina and filtered to remove impurities. The sperm motility (i.e., total and progressive) and concentration were determined by computer-assisted sperm analysis. Biggers, Whitter and Whittingham (BWW), Brackett and Oliphant medium (BO), Human Tubal Fluid (HTF) and Beltsville Thawing Solution (BTS), were semen extenders from other animal species, CAU-A and CAU-B were diluents independently developed by our laboratory. Firstly, the semen was diluted with CAU-B in a ratio of 1:2 (v/v, sperm: CAU-B). After mixing, the semen was centrifuged at 1500rpm for 10 min. The precipitation was retained and added to each tube. Then, the prewarmed extenders were slowly added along the tube wall and mixed by gentle shaking. After cooling to 17°C, diluted semen was placed in an incubator, mixed every 8h, and the sperm motility was analyzed. Meanwhile, we used transrectal palpation andB-mode ultrasound to determine ovarian activity of jennies. Upon detection of a 30-35 mm follicle, jennies were treated with the GnRH analogue deslorelin (GnRH-D) and inseminated with fresh semen diluted appropriately. The pregnancy rate of jennies was evaluated 20 days after ovulation. Statistical analysis was performed by ANOVA. Values are given as mean ± standard error. When diluted semen was stored at 17°C, the motility decreased with the increase of storage time extender. After 16h, sperm in BWW, BTS, BO and HTF extender were all dead. After 48h storage, the motility of sperm in CAU-A (mean 36.14 ± 6.12%) was lower (p < 0.05) than that in CAU-B (53.87 ± 16.25%). Pregnancy rates after insemination with semen diluted in CAU-A, CAU-B, BWW and BO were 30.53%, 34.77%, 29.37% and 30.96%, respectively, and there was no significant difference among groups (p>0.05). However, the pregnancy rate of semen diluted by CAU-B, which contains raffinose and fructose was slightly higher than that of the other groups. In conclusion, the results show that extension of donkey semen in CAU-B extender resulted in a slightly although not significantly improved pregnancy rate. This suggests that the semen extender is important for both, sperm viability and fertilization. This finding may be of significance for breeding and reproduction of donkeys and other equid species.