The effect of cryopreservation on goat semen characteristics related to sperm freezability.

Seminal quality parameters were used to evaluate the effect of freeze-thawing procedure on goat sperm characteristics, and to relate possible changes in sperm parameters to cryopreservation success. Semen samples (n=110) were frozen with TRIS and milk-based extenders and thawed. Sperm quality parameters (motility, morphology and acrosome) were compared between fresh and frozen-thawed samples. Sperm freezability was judged by classifying the semen samples as "suitable" or "not suitable" according to the sperm quality parameters assessed before and after thawing. Fertility data was obtained after cervical insemination with frozen semen doses. The ejaculates were grouped into two categories according to their fertility results. In experiment 1, significant differences were found between semen extenders (P<0.001), bucks (P<0.05) and ejaculates within the same male (P<0.05) in terms of sperm quality. There was no seasonal effect (P>0.05) on the majority of the sperm parameters assessed after thawing. Moreover, significant differences (P<0.001) in semen parameters assessed in fresh semen and frozen-thawed samples were found between groups. The effect of the freeze-thawing procedure on sperm quality parameters was also different (P<0.05) between extenders within the same group. The number of sperm quality parameters that had changed after cryopreservation was lower in "suitable" semen samples before and after thawing. In experiment 2, no differences (P>0.05) in semen parameters assessed in fresh semen and frozen-thawed samples were found between groups. The effect of freezing and thawing on sperm quality parameters were different (P<0.05) between extenders within the same group. Only mean beat cross frequency (BCF) values were significantly higher (P<0.05) in TRIS diluted samples that led to successful pregnancies after artificial insemination. In conclusion, CASA-derived motility parameters, together with traditional semen assessment methods, give valuable information on sperm quality before and after freezing. Therefore, the identification of ejaculates as "good" or "bad" based on fresh and post-thaw semen parameters studied in the present experiment were good indicators of goat semen freezability, although the fertilizing capacity of frozen-thawed goat spermatozoa are not revealed by this quality study.