34 The effect of dilution method of beagle dog semen on the survival rate of cryopreserved spermatozoa after thawing

Abstract

The successful cryopreservation of spermatozoa of the beagle dog for AI is essential for the establishment of the genetic banks of drug detection dogs. The beagle dog is widely used for drug testing and chosen for breeding by breeders. However, the use of cryopreserved beagle semen is limited by the lower number of offspring of dog species. In this study, 3 highly trained beagle dogs were chosen and their semen was cryopreserved for the next generation. The effects of dilution methods of beagle semen were tested using a direct dilution method at RT and a 2-step dilution method at 5°C. As a control group, the effects of a direct dilution method of semen on the percentage of motile sperm and progressive motility were analysed by computer-assisted semen analysis system (SAIS, Korea), and abnormality of spermatozoa was examined by Diff Quik staining. A total of 9 samples from 3 dogs were extended in 4% glycerol containing Tris-egg yolk diluents at approximately 22 to 25°C. The diluted semen was cooled to 5°C within 2 h. The packed 0.5-mL straws were placed 5 cm above the surface of LN for 10 min and then plunged in. A 2-step dilution method was conducted using the same procedures of freezing, but the first dilution was done with glycerol-free diluent. After cooling to 5°C within 2 h, the second diluent with 8% glycerol was added to the same volume of diluted semen at 5°C and stabilised for 1 h. After thawing for 45 s at 37°C, the semen from the 2-step dilution method showed the higher percentage of motile sperm (65.4 ± 6% v. 45.3 ± 8%; P < 0.05) and progressive motility (41.6 ± 5.3% v. 32.3 ± 3.7%; P < 0.05). However, the abnormalities between groups showed no differences. The results suggest that the optimal method for freezing beagle dog spermatozoa is a 2-step dilution process that consists of the first dilution at RT and the second dilution with glycerol at 5°C into diluted semen.