This study was designed to compare the effect of traditional antibiotics streptomycinÁpenicillin (SP) with neomycinÁpenicillin (NP), polymyxinÁpenicillin (PP), and colistinÁpenicillin (CP) in extender against the postthaw quality and bacterial count of buffalo (Bubalus bubalis) bull spermatozoa. Qualifying semen ejaculates (n 018) from three Nili-Ravi buffalo bulls were splits into five aliquots and diluted (50 )10 (6 spermatozoa/ml; 378C) in extender containing SP, NP, PP, CP, or without antibiotics (control). The diluted semen was cooled to 48C in 2 hours and equilibrated for 4 hours. Cooled semen was filled in 0.5 ml French straws at 48C, kept over liquid nitrogen vapors (5 cm) for 10 minutes and then plunged in the liquid nitrogen for storage. For the assessment of post-thaw semen quality (motility, plasma membrane integrity (PMI), sperm viability) and total aerobic bacterial count (TABC), thawing was performed at 378C for 30 seconds. Sperm motility, PMI, sperm viability, and TABC remained similar (P!0.05) in all experimental extenders containing SP, NP, PP, CP, and extender without antibiotics. It is suggested that neomycin, polymyxin, or colistin in combination with penicillin did not deteriorate semen quality and may be suggested to replace streptomycin in traditional antibiotic combination for cryopreservation of Nilli-Ravi buffalo bull spermatozoa.

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