Three experiments have been carried out to investigate the mechanism by which glycerol reduces the fertilizing capacity of boar spermatozoa during storage, and any relationship between this effect and the relatively poor conception rates obtained with deep-frozen boar semen.
The loss of fertilizing capacity in the presence of glycerol was shown to be temperature-dependent, Fertilizing capacity was significantly reduced after 6 hr of incubation at 20°C in the presence of 5 or 10% glycerol, although there was no detectable change in motility or morphology of the spermatozoa. By contrast, there was no effect on fertilizing ability after storage for 6 hr at 5°C or for 30 min at 20°C in the presence of these concentrations of glycerol. Removal of the seminal plasma and a large proportion of the free cytoplasmic droplets did not prevent the reduction in fertilizing capacity. When semen was frozen and thawed, attempts to minimize the exposure of spermatozoa to glycerol did not lead to fertilization when the thawed semen was inseminated through the cervix. It is suggested that at ambient temperature glycerol causes damage to boar spermatozoa which is exacerbated by the stress of freezing and thawing.