الفهرس 
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Abstract
Two experiments were carried out. The first experiment was carried out to investigate the effect of different types of cryoprotective agents (glycerol, dimethyl sulfoxide: DMSO, ethylene glycol: EG, acetamide: AC or lactamide: LA ) and their combinations during thawing- incubation at 37°C for 2 hours on post-thawing sperm motility, freezability and acrosomal damage of spermatozoa. Enzymatic activity aspartate-aminotransferase :AST, alanine- aminotransferase :ALT, acid phosphatase :ACP, alkaline phosphatase :ALP and lactic dehydrogenase :LDH in seminal plasma was also determined. The second experiment was carried out to study the effects of glycerol with DMSO (the best one of cryoprotectants in the first experiment) supplemented with different levels of Glutathione (0, 0.2 , 0.4 and 0.8 mM) on post-thawing sperm motility, freezability, acrosomal damage of spermatozoa, and enzymatic activity, during thawing-incubation at 37°C for up to 2 hours. The conception rates of the cows artificially inseminated with the thawed-frozen semen added eith 7% glycerol without glutathione, 7% glycerol with 0.4 mM glutathione( the best level ), 3.5% glycerol plus 3.5% DMSO without glutathione and 3.5% glycerol plus 3.5% DMSO with 0.4mM glutathione were assessed. The results showed that, the percentages of post- thawing sperm motility and freezability of spermatozoa added with 3.5% glycerol plus 3.5% DMSO were significantly (P<0.05) higher, while the percentage of acrosomal damage of spermatozoa was significantly (P<0.05) lower than other cryoprotective agents or their combinations . The thawed- frozen bull semen extended 3.5% glycerol plus 3.5% DMSO was significantly (P<0.05) lower the amounts of AST, ALT, ACP, ALP and LDH enzymes into the extracellular medium than other cryoprotective agents or their combinations ( Experiment 1 ). Supplementation of glutathione at levels of 0.2, 0.4 and 0.8 mM to the thawed-frozen bull semen significantly (P<0.05) higher the percentage of post-thawing sperm motility and freezability of spermatozoa, while significantly (P<0.05) lower the percentage of the acrosomal damage than free glutathione medium. The thawed- frozen bull semen extended with 3.5% glycerol plus 3.5% DMSO added with 0.2, 0.4 or 0.8 mM glutathione was significantly (P<0.05) lower, the amounts of AST, ALT, ACP, ALP and LDH enzymes into the extracellularr medium than free glutathione medium. The highest (P<0.05) conception rate (85.0%) was obtained for cows artificially inseminated with the thawed-frozen semen extended with 3.5% glycerol plus 3.5% DMSO supplemented with 0.4 mM of glutathione .