The effectiveness of gentamicin or polymyxin B for the control of bacterial growth in equine semen stored at 20 degrees C or 5 degrees C for up to forty-eight hours.

The research paper evaluates the efficiency of two antibiotics, gentamicin and polymyxin B, in controlling bacterial growth in horse semen stored at two different temperatures for up to forty-eight hours.

Objective of the Study

• The study was conducted to assess the effectiveness of gentamicin and polymyxin B in preventing bacterial growth when added to a semen extender in horse semen samples stored at 20°C or 5°C for up to 48 hours.

Methodology

• The researchers used semen samples from three stallions.
• Each ejaculate was subjected to six different treatments – semen+extender (SE); SE+gentamicin (100 micrograms/mL); SE+polymyxin B (1000 units/mL) and the same treatments added with Pseudomonas aeruginosa bacteria.
• The semen samples were then retained at the chosen temperatures (20°C or 5°C), and samples were taken for bacteriological analysis after 2, 8, 24, and 48 hours.

Outcomes

• After two hours of preservation at both temperatures, all SE aliquots showed the presence of nonspecific bacteria. The bacterial count did not vary in samples stored at 5 degrees C, but increased 3-4 times in those stored at 20 degrees C after 48 hours.
• In comparison, the samples treated with either antibiotic showed very low numbers of nonspecific bacteria after 2 and 8 hours at both temperatures.
• This number remained stable up to 48 hours at 5°C, whereas an increased bacterial count was observed at 24 and 48 hours at 20°C.
• The researchers noted a decrease in the number of P. aeruginosa cells between 24 and 48 hours in SE aliquots at 5°C. The presence of the two antibiotics appeared to inhibit the growth of P. aeruginosa rapidly.
• At 20°C, an increase in P. aeruginosa growth was observed between 8 and 24 hours in the SE aliquots, but the presence of the antibiotics seemed to halt the bacterium’s growth almost entirely.

Conclusion

• The results suggest that gentamicin and polymyxin B are effective antibiotics for controlling bacterial growth in horse semen stored at 20°C and 5°C. The results indicate that these antibiotics can maintain the quality of stored horse semen for artificial insemination purposes by suppressing unwanted bacterial growth, specifically P. aeruginosa.