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 48 HOURS

Semen from three stallions was used to evaluate the effectiveness of t wo antibiotics added to semen extender for samples stored at 20-degree s-C or 5-degrees-C for up to 48 hours. Each ejaculate was divided into six different treatments: semen + extender (SE); SE + gentamicin (100 mug/mL); SE + polymyxin B (1000 units/mL); and each of the above trea tments inoculated with Pseudomonas aeruginosa ATCC 27853. Sampling of diluted semen for bacteriological analysis was performed after 2, 8, 2 4 and 48 hours of preservation at either temperatures. The presence of nonspecific bacteria was noted after two hours in all SE aliquots. Th e number of bacteria did not change in samples stored at 5-degrees-C, while in samples preserved at 20-degrees-C, it increased by three to f our times after 48 hours. In semen aliquots treated with either of the antibiotics, the number of nonspecific bacteria was very low after tw o and eight hours at both temperatures. This number remained stable up to 48 hours at 5-degrees-C, while an increase was noted at 24 and 48 hours at 20-degrees-C. At 5-degrees-C, the number of P. aeruginosa cel ls tended to decrease between 24 and 48 hours in SE aliquots. The pres ence of gentamicin or polymyxin B appeared to rapidly inhibit growth o f P. aeruginosa. At 20-degrees-C, growth of P. aeruginosa increased be tween 8 and 24 hours in SE, while the presence of antibiotics almost c ompletely inhibited the growth of the bacterium. In conclusion, gentam icin and polymyxin B appeared effective for the control of P. aerugino sa at either temperature, but nonspecific bacteria increased after 24 and 48 hours at 20-degrees-C.