Cryopreservation has been reported to damage approximately 40e50% of viable sperm in bull semen.
The present study was undertaken to assess the cryo-effectiveness of glycerol (GLY), ethylene glycol (EG),
dimethyl sulfoxide (DMSO) and propylene glycol (PND) as cryoprotectant during the cryopreservation of
Nguni bull semen. Semen was collected from 18 Nguni bulls and evaluated macroscopically and
microscopically for sperm parameters. Thereafter, the semen samples were diluted with egg-yolk citrate
extender supplemented with either 12% GLY or DMSO or EG or PND cryoprotectant. Semen samples were
loaded into straws and placed into a controlled rate programmable freezer and stored in a liquid nitrogen
tank. Following semen thawing, artificial insemination (AI) was done on synchronized Nguni cows. The
in vitro fertilization (IVF) was conducted on cow's oocytes to test the fertilizing ability. Data was analyzed
with the aid of ANOVA. A significant difference (p < 0.05) was recorded between fresh total sperm
motility rate (94.7 ± 2.6%) and frozen-thawed sperm total motility rate with GLY (77.8 ± 11.0%), EG
(20.4 ± 10.1%), DMSO (15.7 ± 11.9%) and PND (11.2 ± 11.3%). Interestingly, a positive correlation between
total sperm motility and pregnancy rate (r ¼ 0.42) was recorded. However, a negative correlation of
Nguni sperm parameters with IVF (r ¼ 0.53) was obtained. The freezing-thawing process did reduce the
Nguni sperm total sperm motility percentage.