Abstract   

Ejaculates were collected from 18 Nili-Ravi buffalo bulls belonging to young (3-4 year), adult (6-8 year) and old (12-15 year) age groups during the low and the peak breeding seasons. These ejaculates were diluted with lactose-fructose-egg yolk glycerol extender, frozen and stored at -196°C at least for 24 hrs. Frozen- thawed ejaculates were used to inseminate 971 buffaloes with clinically normal reproductive tract. These buffaloes were examined for pregnancy through rectal palpation two months after insemination. The results showed that semen from young (42.81 ± 1.48%) and adult (45.14 ± 1.37%) bulls had higher (P<0.05) tertility rate than old (37.46 ± 1.75%) bulls. Similarly, semen samples collected during the peak breeding season showed higher (P<0.05) fertility (44.87 ± 1.01 %) than those collected during the low breeding season (38.73 ± 1.72%). Fertility of frozen-thawed semen was conelated positively with post-thaw motility (r = 0.40, P<0.05) and liveability (r = 0.44, P<0.Ol) of spermatozoa. Abnormal sperm heads (r = -0.52, P<0.Ol) and abnormal acrosomes (r = -0.41, P<0.05), and GOT (r = -0.45, P<0.01) and GPT (r = - 0.49, P<0.01) activities in frozen-thawed seminal plasma showed negative conelations with fertility.