Inclusion of supplemental antibiotics (amikacin – penicillin) in a commercial extender for stallion semen: Effects on sperm quality, bacterial growth, and fertility following cooled storage.

The research study investigates the effectiveness of including additional antibiotics in a commercial semen extender for horses, and how it impacts sperm quality, bacterial growth, and chances of fertility after cool storage.

Research Context and Methodology

• The authors of this study set out to measure the effectiveness of adding amikacin sulfate and potassium penicillin G (AP) to a commercial semen extender, INRA-96®, that already contains specific original antibiotic components. The main purpose of this supplementation is to reduce bacterial contamination that can affect sperm quality and fertility.
• The research was divided into three major experiments. Experiment 1 was focused on comparing two sources of amikacin with another antibiotic combination and a no-supplemental antibiotics control group. The goal was to consider impacts on sperm quality and commensal bacterial growth.
• Experiment 2 examined the effects of increasing doses of amikacin sulfate and potassium penicillin G on sperm quality and bacterial growth. Specifically, five different doses (AP-1000, 2000, 3000, 4000 or 5000 μg-IU/mL) were evaluated at two different time periods: 30 minutes after exposure and 24 hours after cool storage.
• The final experiment, Experiment 3, was a breeding trial to determine the impact of high-dose AP supplementation on the pregnancy rates of mares bred with cool-store semen.

Findings and Conclusion

• This study found that the addition of amikacin and potassium penicillin to INRA-96® did not have a significant effect on sperm quality, regardless of concentration or the time period evaluated. In Experiment 1, no differences were detected in sperm quality among the different treatments 30 minutes after exposure or after 24 hours of cool storage.
• Despite the preservation of sperm quality, the researchers observed a significant decrease in commensal bacterial growth in the mixtures containing the antibiotics additional to the original formulation.
• In Experiment 2, it was seen that high doses of the antibiotics caused a slight reduction in sperm motility and viability in the early stages, but this difference did not persist after 24 hours of cool storage.
• The addition of a high dose of AP did not result in a statistically significant increase in pregnancy rates in Experiment 3, but there was a noticeable decrease in bacterial growth in semen samples contaminated with Pseudomonas aeruginosa, and Klebsiella pneumoniae when compared to the original extender that lacked additional antibiotics supplementation.
• Generally, the results indicated that supplementing the commercial semen extender (INRA-96®) with amikacin and penicillin effectively controlled commensal bacterial growth without affecting sperm quality. A higher dose of the antibiotics could be safely added to improve the antibacterial activity against commensal and potentially pathogenic bacteria, while preserving sperm quality and fertility rates during the cold storage of semen.
• Based on these results, the authors recommend the use of the common dose of 1000 μg/mL – 1000 IU/mL as a precautionary measure when contamination of ejaculates with normal bacteria is evident. A high dose (5000 μg/mL – 5000 IU/mL) could be used as a control method for potentially pathogenic bacteria.