Evaluation of Bull Semen Quality and Sperm DNA Integrity during Cryopreservation with Different Cryoprotectants

The fertility rate in dairy cattle with cryopreserved semen significantly depends on the reduction of the toxic effects on the sperms induced during cryopreservation. DNA integrity in sperm is vital for the precise transmission of genetic information and therefore the production of high yielders and maintenance of good health in future generations. The reliable and consistent assessment of sperm motility can be succeeded by Computer Assisted Semen Analyzer (CASA). Ten ejaculates were collected from Frisian bulls kept at Centre of excellence for bovine genetics (CEBG) Renala Khurd District Okara. The deleterious effects of three cryoprotectants glycerol, dimethylsulfoxide (DMSO) and ethylene glycol as a constituent of tris-egg yolk-citrate extender were compared on diluted post thawed cryopreserved Frisian bull semen. The quality of semen in terms of viability/motility/progressive velocity was determined with computerized external real image optical system (CEROS) and sperm DNA fragmentation was quantified with comet assay using single cell gel electrophoresis (SCGE) technique. Glycerol was the least followed by DMSO and ethylene glycol was the most toxic cryoprotectant both for semen quality and sperm DNA fragmentation. The present study suggests that sperm DNA fragmentation is an associated feature of semen cryopreservation resulting into cell death (non-motile sperms) and glycerol as a cryoprotectant constituent of tris-egg yolk citrate extender offers a better protection for storage of cryopreserved Frisian bull semen in liquid nitrogen.