Influência de sistemas de refrigeração sobre a qualidade do sêmen ovino criopreservado em palhetas

Different types of cooling systems of ram semen were evaluated by the measurement and comparison of cooling rates and their effects on the post-thawing quality.  Motility, vigor, morphology damages, viability and acrosomal status were tested at the end of 90 minutes of cooling and post-thawing. Regarding post-thawed semen, the same parameters were used, in addition to the assessment of the integrity of the plasmatic membrane, and the resistance test by the incubation of semen at +37oC for 4 hours. Semen refrigeration was carried out in a domestic refrigerator and in a horizontal refrigerator. To control the temperature drop of semen in both equipments, the slats were disposed between plastic bags containing water at +32oC, constituting four combinations of cooling procedures: RS (refrigerator without bag), RC (refrigerator with bag), BS (horizontal refrigerator without bag) and BC (horizontal refrigerator with bag), resulting in four cooling rates: -1.4oC/min, -0.4oC/min, -2.9°C/min and -0.45oC/min, for RS, RC, BS and BC, respectively. At the end of the cooling period, BS treatment showed the lowest percentage of sperm motility (P<0.05), the lowest mean of live spermatozoa with intact acrosome, and the highest mean of dead spermatozoa with intact acrosome (P<0.05).  As for morphological defects, BS treatment had the highest mean whereas the systems RC and BC resulted in the lowest means. There was no significant difference among treatments in relation to frozen-thawed semen at the end of the resistant test. It was concluded that the different cooling rates affected ram semen at the end of cooling stage but not at post-thawing. KEYWORDS: Cooling protocols, cryopreservation, ovine, semen.