Cryo-damage of Canine Semen and Its Minimization: Present Scenario

Introduction Although dog was the first species to be used for Artificial Insemination (AI) and become pregnant by Spallanzani in 1780, very little work has been done on preservation of dog semen to exploit the full genetic potential of pedigree males. Frozen semen is now inseminated routinely in cattle, sheep and goats and much research has been carried out with regard to the optimum conditions for its use in these species. In many countries there has been limited use of frozen dog semen, owing mainly to the poorer fertility when compared with fresh or chilled semen and also, to some extent, owing to the regulations controlling the use of artificial insemination. The use of frozen semen has, therefore, been limited to inter-continental transfer of genetic material and long-term storage of spermatozoa. Although there have been many reports of the successful freezing and thawing of dog semen, the majority of workers have adopted methodology designed for other species, and investigations have merely comprised comparisons between diluents (Foote, 1964; Andersen, 1972; Davies, 1982; Yubi, 1984). Thorough investigations have been attempted in only a limited number of studies (Olar, 1984; Smith, 1984) and these have limitations in that the end point has rarely been fertility in any suitable number of bitches. Conception rates with frozen-thawed dog semen have generally been poor when compared with those of other species. It has been reported that frozen-thawed spermatozoa did not exhibit the vigorous motility of freshly ejaculated spermatozoa and that consequently their survival within the female tract and their fertilizing ability are likely to be reduced. This may be related to the poor penetration of oocytes by frozen-thawed (compared with fresh) dog spermatozoa (Froman et al. 1984). The problem is not entirely the result of poor semen quality after thawing, but also of the difficulty of identifying the optimal time for insemination of the bitch. Cryopreservation of canine semen like that of other animal species is used for artificial insemination and for storage of semen samples from valuable dog breeds (Ivanova et al., 1992). The cryopreservation of dog semen is becoming increasingly popular since it allows for the transporting of genetic materials both within and between countries. Since the first birth of line offspring from frozen dog semen (Seager, 1969), dog breeders world-wide have put increasing pressure on the scientific world to be part of the progress in reproduction biotechnology (Farstad, 1996). And when developing new techniques for cryopreservation of spermatozoa, the goal is to minimize the damage caused to spermatozoa by the process in order to recover a maximum number of viable spermatozoa. The cryopreservation process results in reduced fertility compared with fresh semen. It has been shown that this arises from a combination of both loss of sperm viability and an impairment of function in the population of survivors. This situation needs to be borne in mind when strategies to improve the results are contemplated. We need to consider not only the cryopreservation protocol to optimize the number of survivors, but also the functional ability of the surviving population.