The effects of antibiotic type and extender storage method on sperm quality and antibacterial effectiveness in fresh and cooled-stored stallion semen.
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Two experiments were conducted to evaluate the effects of antibiotic-containing extender of on sperm quality and control of bacterial growth. In Experiment 1, ejaculates were diluted in extender containing no antibiotics, potassium penicillin G-amikacin disulfate (PEN-AMIK), ticarcillin disodium-potassium clavulanate (TICAR-CLAV), piperacillin sodium/tazobactam sodium (PIP-TAZ), or meropenem (MERO). In freshly extended semen, only slight differences were detected among some antibiotic treatments for total sperm motility, curvilinear velocity, and viable acrosome-intact sperm (P<0.05). In cool-stored semen, slight differences were also detected among certain antibiotic treatments for curvilinear velocity and chromatin integrity (P<0.05). In Experiment 2, ejaculates were diluted in extender and subjected to no bacterial spiking, or inoculated with lower or higher doses of K.pneumoniae or P.aeruginosa. Following cooled storage of semen, colony forming units/ml (CFU/mL) were less in PEN-AMIK (706244) and MERO (15761076) treatment groups than in TICAR-CLAV (46781388) or PIP-TAZ (81083198) treatment groups (P<0.05). The CFU/mL were lower in all antibiotic-containing treatment groups than the control group (184784374; P<0.05). The percentage of culture plates containing no bacterial growth in unspiked semen was greater in PEN-AMIK (75%) than PIP-TAZ (15%) or TICAR-CLAV (20%; P<0.05). The percentages of culture plates containing no bacterial growth in semen spiked with a lower doses of K.pneumoniae or P.aeruginosa were higher in PEN-AMIK (70% and 50%, respectively) then in all other treatment groups (0-40% and 0-15% for K.pneumonia and P.aeruginosa, respectively; P<0.05); however, complete control of bacterial load was only modest even with PEN-AMIK. In both experiments, freezing and thawing extender prior to use did not have any appreciable detrimental effect on sperm quality or antibiotic efficacy. In summary, all antibiotics tested had minimal effects on measures of sperm quality in fresh or cool-stored semen extenders; however, PEN-AMIK, followed by MERO, yielded the best results in terms of antimicrobial efficacy. None of the antibiotic types controlled bacterial growth, in comparison with the antibiotic-free control group, when extended semen was spiked with a high concentration of Pseudomonas aeruginosa. Cooled storage of extended semen reduced bacterial growth in comparison with freshly extended semen.