ABSTRACT
Semen was collected from six stud dogs to compare five extenders in the semen freezing process. Each ejaculate was divided in five parts and added to tris-fructose-citric acid, glicine, lactose, skim milk and tris-fructose-citrate extenders. The semen was diluted at 37ºC in extenders without glycerol, in the ratio 1:1 and cooled for 60 minutes to reach a 5ºC temperature. Then, extenders with glycerol in the ratio of 2:1 were added to give the final prefreezing concentration of 4 per cent of glycerol. The diluted semen with the cryoprotectant was maintained for a further 60 minutes in refrigeration to equilibrate the spermatozoa in the glycerol and packaged in 0.5 ml plastic straws. The straws were maintained for 30 minutes in vapor, plunged and stored in liquid nitrogen. Sperm morphology was evaluated before and after freezing, whereas progressive motility (per cent) and velocity of forward progression (0-5) were appraised in different periods of the freezing process. The extender tris-fructose-citric acid showed the best post thaw progressive motility and velocity of forward progression compared to the others extenders. Semen freezing increased major sperm morphological abnormalities, regardless of the extender