الفهرس 
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Abstract
The present study was carried out by using frozen semen of cow bulls and buffalo bulls. The frozen semen was produced either locally or imported from France. The locally produced frozen semen was processed at Abbasia Frozen Semen Centre for Buffaloes and Beni-Suef Frozen Semen Centre for Cattle (General Orgnization for Veterinary Services). The frozen semen processed from a total number of 22 buffalo bulls and 23 cow bulls (local 9 Holstein-Friesian and 2 Brown-Swiss as well as imported 12 French breeds 6 Trantase and 6 Abandance). Statistical analysis of the obtained data revealed the following: 1)A highly significant increase in percentage of post-thawing motility (PTM) of bull spermatozoa (41.11 ± 0.81%) in comparison with that of buffalo spermatozoa (35.89 ± 1.05%); it seemed to vary significantly between Brown-Swiss (44.64 + 1.85%), Friesian (37.59 ± 0.67%) and French (44.17 ± 1.30%) breeds; the percentage of PTM of bull and buffalo bull spermatozoa differed significantly between the different age groups as it was superior at 5 — 10 years old buffalo bulls (40.42 ± 2.64%) and at 10 — 15 years old bull (42.50 ± 1.68%); the percentage of PTM of spermatozoa fluctuated between the duration of storage of the frozen semen as it was superior for bull semen stored for two years (44.29 + 1.95%) and for buffalo semen stored for three years in liquid nitrogen (38.21 ± 2.60%). 2)The percentage of live spermatozoa (PLS) was always higher than the percentage of PTM of spermatozoa, similar trend appeared for both percentages in all occasions. Thus, effects of species, breed, age of the bull and the duration of storage of the frozen semen on PLS might be expected. 3) Storage of the frozen semen has no significant effect on the percentage of intact acrosome (PIA) of spermatozoa between cow bulls (79.15 ± 0.35%) and buffalo bulls (79.45 ± 0.40%); the difference was not significant between Brown Swiss (79.21 ± 0.71%), Friesian (79.15 ± 0.58%) and French (79.08 ± 0.40%) breeds; the PIA of bull and buffalo bull spermatozoa was found to decrease non-significantly by advancing the age of the bull. The PIA of buffalo frozen spermatozoa showed a significant increase in semen stored for one year while the cow bull frozen spermatozoa showed a non-significant difference in PIA of spermatozoa between the different storage periods of the frozen semen. 4) There was a significant reaction to the hypo-osmotic swelling test (HOST) in buffalo frozen spermatozoa (23.02 ± 0.72%) more than that in cow bull frozen spermatozoa (17.81 ± 0.71%); the reaction to HOST was not significantly different between Brown-Swiss, Friesian and French breeds; also, age of the bull did not induce any significant reaction to the HOST of spermatozoa of cow bulls and buffalo bulls up to 10 — 15 years of age. The reaction of buffalo frozen spermatozoa to HOST decreased significantly in spermatozoa stored for one year compared to other storage periods of the frozen semen while in cow bull frozen spermatozoa the reaction to HOST was non significant between the different storage periods of the frozen semen. 5)The semen quality test (SQT) appeared significantly higher with buffalo frozen semen (2.11 ± 0.14) than that with cow bull frozen semen (1.29 ± 0.03). The semen quality test showed a non significant difference between the different breeds. Afluctuant results were noticed in the SQT between the different ages of buffalo bulls. A highly significant increase in SQT for cow bulls aged 10-15 years when compared to other ages. The SQT for cow and buffalo bulls frozen semen revealed a highly significant increase in semen stored for two and three years in comparison with that stored for one year. 6)The conception rate appeared significantly greater with cow bull frozen semen (65.75 ± 0.59%) than that with buffalo frozen semen (62.04 ± 0.62%). The French frozen semen showed a highly significant increase in the conception rate in comparison with the Brown-Swiss and Friesian frozen semen, it seemed to be nearly comparable for the different age groups. The duration of the storage of the frozen semen has no appreciable influence on the conception rate of buffalo bulls while the conception rate showed a highly significant increase for cow bull frozen semen stored for three years. from the present study it can be concluded the following: 1) The storage efficiency of the frozen semen can be assessed by estimating the hypoosmotic swelling test and semen quality test for buffalo bulls and the percentage of the post-thawing motility of spermatozoa for cow bulls. 2)Storage of the French frozen semen seemed much better than that of other breeds at least under circumstances of the present study. 3)The storage efficiency of the frozen semen seemed more fluctuant between the different ages of bulls and buffalo bulls, in the mean time, the age of the buffalo bulls used in the production of the frozen semen might not exceed 10 years may be extended to 15 years with regard to cow bulls to obtain a high quality frozen semen and high fertility. 4)The change in efficiency of the stored frozen semen in relation to the duration of storage seemed to be more related to the changes in the processing, storage and handling techniques of the frozen semen more than the duration of the storage itself.