BACTERIOLOGY OF PRESERVED STALLION SEMEN AND ANTIBIOTICS IN SEMEN EXTENDERS

Three experiments were conducted to evaluate the effects of different antibiotics in a milk-glucose semen extender on motility of equine spe rm and elimination of bacteria following storage of extended semen in vitro. In Experiment 1, 7 antibiotics were compared: amikacin, gentami cin, streptomycin, potassium penicillin sodium penicillin, ticarcillin . and polymixin B. In Experiment 2, 3 antibiotic treatments were compa red: potassium penicillin G, amikacin, or a combination of potassium p enicillin G and amikacin. In Experiment 3, 3 antibiotic treatments wer e compared: potassium penicillin G-amikacin ceptiofur, and a combinati on of ticarcillin and clavulanic acid (Timentin). Control treatments ( antibiotic-free extender) were included in each experiment. Six motili ty variables were evaluated: percentage of motile sperm; percentage of progressively-motile sperm; percentage of rapidly-motile sperm; mean curvilinear velocity; mean average path velocity; and mean straight-li ne velocity. In Experiment 1, mean percentages of motile, progressivel y motile and rapidly motile sperm were lower (P < 0.05) in semen expos ed to polymixin B then in other treatments. Mean average-path velocity of sperm in extender containing polymixin B was lower (P < 0.05) than that of all other treatments, with exception of control or,ticarcilli n. Mean straight-line velocity of sperm in extender containing polymix in B was lower (P < 0.05) than that of all other treatments, with exce ption of control, streptomycin or ticarcillin. Semen samples containin g gentamicin, amikacin, streptomycin, or potassium penicillin were mor e effective (P < 0.05) at eliminating bacterial growth than those samp les containing polymixin B. Semen samples containing gentamicin were a lso more effective (P < 0.05) at eliminating bacterial growth than tho se samples containing ticarcillin or sodium penicillin. In Experiment 2, mean percentage of rapidly-motile sperm, and mean curvilinear, aver age-path, and straight-line velocities were greater (P < 0.05) for pot assium penicillin-amikacin than values for all other treatments. In 2 of 3 stallions, an effect of treatment on percentage of motile sperm w as detected (P < 0.05). For one stallion, mean motility of potassium p enicillin-amikacin was greater (P < 0.05) than that of all other treat ment groups. For another stallion, mean motility of the control was lo wer CP < 0.05) than that of the other treatments. Following storage, p otassium penicillin (16/18 [89%]) or potassium penicillin-amikacin (17 /19 [94%]) were more effective (P < 0.05) at controlling aerobic and a naerobic bacterial isolates in semen specimens than was amikacin (10/1 8 [56%]). In Experiment 3, a difference among treatment groups for mot ility variables was not detected (P > 0.05). No bacterial growth was r ecovered in antibiotic-treated semen, with exception of Micrococcus sp . (2 colonies) which were isolated from one semen specimen treated wit h ceptiofur. (C) 1998 by Elsevier Science Inc.