Influence of sugars and osmoregulators on motility and viability of cooled and frozen-thawed ram semen

The aim of the study was to determine the effect of sugars and osmoregulators on the viability of frozen-thawed ram semen in a Tris-based diluent. Two experiments were conducted to evaluate the effect of sugars (fructose, glucose, sucrose and raffinose) and two osmoregulators (hypotaurine and taurine) on the viability of ram sperm. In experiment 1, each of the four sugars (fructose, glucose, sucrose and raffinose) was added (500 mg%) to the diluents. Semen was collected from 15 rams once a week using an artificial vagina, diluted, cooled slowly to 5°C over 2 h, frozen in the form of pellets, and plunged into liquid nitrogen. The frozen semen was thawed, and sperm viability was calculated 3 h after thawing. In experiment 2, two osmoregulators, hypotaurine (0.20 and 0.40 mg/ml) and taurine (2 and 4 mg/ml), were added to Tris-based raffinose diluent. Motility and viability rates were calculated. The results showed that motility was gradually significantly (P < 0.05) improved by using 500 mg% raffinose in the Tris-based diluents after dilution at 30°C and before freezing at 5°C. Post-thawing motility and viability rates were highest (P<0.05) when raffinose was used in Tris-based diluent for cryopreservation of ram semen. In vitro supplementation of the semen diluent with 4 mg/ml taurine had a beneficial effect on the motility and viability of ram spermatozoa after dilution at 30°C and before freezing at 5°C. The same trend was observed after freezing-thawing and 3 h post-thawing. In conclusion, 500 mg% raffinose was a more suitable sugar component for treatment of ram spermatozoa in Tris diluent than fructose or glucose, while 4 mg/ml of taurine in Tris-raffinose medium exerted a beneficial effect on the motility and viability of ram sperm at cooling and post-thawing.