الفهرس 
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Abstract
This study aimed to investigate the effect of adding different types and levels of cryoprotectants on sperm viability during different freezing processes of buffalo semen. Also, the effect of different types and levels of antioxidants on sperm motility and acrosome status in post-thawed semen was studied. Five sexually mature buffalo bulls aged 7-10 years were used for semen collection by means of an artificial vagina. Ejaculates were obtained from each buffalo bull twice/week for 10 weeks collection period (100 ejaculates). The main extender used for semen dilution was Egg Yolk-Citrate-Tris with different types (glycerol, GL; dimethyl sulfoxide, DMSO and ethylene glycol, EG) and levels (5, 7 and 10% for each) of cryoprotectants. Then, semen was frozen in liquid nitrogen (LN) and thawed at 37°C/30 sec. Percentage of progressive motility of spermatozoa was determined pre- and post-dilution, post- equilibration period for 4 or 6 h, post-thawing after 24 h freezing period. Also, Tris-egg-yolk-citrate extender containing 7% glycerol. Total of 10 extenders, 9 with 3 types and 3 levels of antioxidant, including catalase (250, 500 and 1000 IU), glutathione (GSH, 0.4, 0.8 and 1.2 mM) and ascorbic acid (AA, 0.5, 1.0 and 1.5 g/l) were compared to unsupplemented extender (control). Semen was extended with different types and levels of antioxidants, frozen in LN (-196oC) and thawed at 15oC/60 sec, 35oC/30 sec and 55oC/15 sec. Percentages of sperm motility and damage acrosome were determined in post-thawed semen. Conception rate was detected in 100 sexually mature buffalo cows (10 animals in each group) artificially inseminated with different types and levels of antioxidants. These results indicated beneficial effects on improving sperm motility when buffalo semen was extended in Tris-based extender containing 7% glycerol as a cryoprotectant agent. In addition, Tris-based extender containing catalase at a level of 1000 IU in frozen semen thawed at a rate of 55oC/15 sec showed the highest post-thawing motility and the best fertilizing capacity of buffalo spermatozoa. Supplementation of semen diluted with Tris-extender with natural antioxidant (ascorbic acid) a level of 0.5 g/l or 0.4 mM of GSH resulted in buffalo bull spermatozoa to maintain their fertilizing capacity at cooling temperature (5oC) for 72 hours.