Effect of thawing regimens on the morphofunctional state of canine spermatozoa

The effect of 2 thawing regimens (37 degrees C for 8 sec and 55 degrees C for 5 sec) was followed up on semen parameters related to the viability of canine spermatozoa. The ejaculates were frozen in the form of pellets on dry ice in the following cryoprotective extenders: TRIS-fructose (TF), TRIS-glucose (TG), and sucrose-lactose (SL). For the 3 extenders, significant differences were found in the percentage of motile spermatozoa and their survival rate up to 300 min in favor of the 55 degrees C vs the 37 degrees C thawing regimens. Structural changes such as swelling, breakage and absence of acrosomes were observed in the samples frozen in the 3 cryoprotective extenders. A considerably lower percentage of spermatozoa with damaged acrosomes was recorded at 55 degrees C in comparison with that found at 37 degrees C (P < 0.05 for TG, TF and SL). Enzymocytochemical analysis was made of NADH-tetrazolium reductase activity in thawed spermatozoa. Cells showing moderate and strong intensity of the cytochemical reaction were found after both regimens of thawing. The percentage of spermatozoa manifesting strong intensity of the reaction was comparatively higher after thawing at 55 degrees C (31.8 +/- 2.06) than at 37 degrees C (23.7 +/- 1.41; P < 0.01). The thawing regimens were the factors that exerted influence on the morphofunctional state of frozen canine spermatozoa, irrespective of the cryoprotective extenders used, in the present study. Thus the optimal preservation of sperm viability was achieved by thawing at 55 degrees C for 5 sec.