Spermatozoa quality of cryopreserved canine semen. II - Effect of cooling procedures

A study on cooling and equilibration procedures was performed in canine semen for evaluating the effects on in vitro characteristics of cryopreserved spermatozoa. Semen from three stud dogs was collected weekly during five weeks for the experiment protocol. The cooling systems were accomplished in a programmable cells freezer or in a polystyrene foam container. The evaluations employed were sperm motility and forward progression, and plasmatic membrane and acrosome integrity using the hypo-osmotic swelling test (HOS-T) and phase contrast microscopy, respectively, and semen longevity, using the thermo-resistance test. The comparative analysis of the cooling systems has showed that there was no difference (P>0.05) between programmable freezer and the polystyrene container, immediately after cooling and equilibration times. Although after freezing and thawing the results of forward progression, HOS-T and acrosome integrity were equal for both cooling systems, best results for the motility and thermo resistance tests (P<0.05) were observed in the polystyrene container. The cooling rate in this system was of approximately -0.45<degrees>C/min and for the programmable freezer was of -0.55 degreesC/min. The temperature fall was not constant in the polystyrene container and dropped faster in the beginning of the cooling time. It seems that this cooling rate as the polystyrene container favored the maintenance of spermatozoa energy sources. The tests results for both procedures were in agreement to the standard values for the freezing semen in dogs.