The study was conducted to evaluate the efficacy of the antibiotic combinations, streptopenicillin (SP) and gentamicin, tylosin,

lincomycin and spectinomycin (GTLS) for the control of bacterial load and improvement of semen quality in Frieswal bulls (Holstein Fresian × Sahiwal). Staphylococcus, Proteus, Klebsiella, Bacillus, Actinomyces, E. coli were isolated from the frozen semen. The cultural sensitivity testing of the bacterial isolates showed that Gentamicin and Spectinomycin were most effective while penicillin was least effective against the isolated organisms. For the study, ejaculates from bulls (n = 6) were taken twice weekly for 3 weeks. Each ejaculate was divided into 3 aliquotes. Tris egg yolk citric acid buffer extender was used to dilute the semen samples. Streptopenicillin antibiotic combination was used in one aliquote while gentamicin, tylosin, lincomycin and spectinomycin were used in 2nd aliquote. In 3rd aliquote, no antibiotic was used and kept as untreated control. Semen straws were frozen from all three aliquots and semen quality parameters were analyzed as per standard procedures. Significantly better bacterial load control (p < 0.05) was observed in GTLS antibiotic combination added group as compared to SP group. Significantly (p < 0.05) higher post thaw sperm motility was recorded at 0 min, 30 min and 60 min after incubation at 37oC in GTLS treated group as compared to SP treated group. Percentage of hypoosmotic swelling test and acrosome integrity were found significantly (p <0.05) higher in GTLS antibiotic group as compared to SP group. As regards to live percentage of spermatozoa, both SP and GTLS group had significantly higher live sperm concentration as compared to non-antibiotic group while they did not differ significantly with each other. Sperm abnormalities of head, mid piece and tail did not differ significantlywithin all the three groups. The study concludes that gentamicin, tylosin, lincomycin and spectinomycin combination is better than streptopenicillin in controlling bacterial load and improving semen quality.

Highlights

• Gentamicin, tylosin, lincomycin and spectinomycin (GTLS) antibiotic combination was effective in controlling bacterial load of bull semen.
• GTLS antibiotic combination was shown to improve sperm motility, sperm membrane integrity, and acrosomal intactness following cryopreservation.