The inability of turkey spermatozoa to successfully survive the freezing/thawing process has been a major limitation to the use of frozen sperm doses in the turkey breeding industry and to the expansion of genetic re- sources to preserve the biodiversity of this bird.
The high sensitivity of turkey sperm to cryopreser- vation is thought to be a consequence of the bird’s metabolic profile of cell membrane lipids, such as its cholesterol/phospholipid ratios, influencing membrane fluidity [16], of the biochemical changes occurring dur- ing cryostorage [9] and of the low osmotic tolerance shown by the sperm cells of this species [10].
In chicken spermatozoa, surface carbohydrates are modified during cryopreservation, and the cryopro- tectant and freeze/thaw rates used seem to affect the extent of this modification [40]. Although this has not yet been the subject of investigation, this could also occur in turkey spermatozoa.
Despite the lowered life-span of turkey sperm de- tected in our post-thaw study, large differences in sperm cryosurvival were related to the different treat- ments tested. Thus, even a small change in the freezing/ thawing process was able to impact the success of cryopreservation.
Given that numerous factors may affect the success of the pellet cryopreservation process for turkey semen besides those identified here, future studies should ad-
dress such factors or their different combinations using a similar statistical model and PCA.
In conclusion, through PCA we were able to define a single target measure of the post-thaw quality of turkey semen. Although post-cryopreservation sperm quality was low relative to its starting quality, the method proposed was able to identify a combination of steps in the freezing/thawing process as the best treat- ment procedure among 192 procedures considered.
The high variation in post-thaw semen quality ob- served here determines a need for further efforts to better evaluate the factors and their interactions influ- encing the semen pellet cryopreservation procedure.
Although our findings are still far from fulfilling the requirements for the commercial use of frozen turkey semen, the post-thaw sperm quality achieved could be sufficient to create sperm banks for gene preservation programs, provided this quality is confirmed in vivo.
Acknowledgments