D. D. Varner

Developments in stallion semen evaluation

The conventional approach to evaluation of stallion semen dates back several decades, and includes evaluation of spermatozoal concentration, semen volume, spermatozoon morphological characteristics, and spermatozoal motility patterns initially and following in-vitro storage. While an analysis performed in this manner does have predictive value, incorporation of some more newly developed techniques may improve the predictive value of the examination. This communication addresses some newer tests that can be applied today for evaluation of semen, as well some tests that may be available in the coming years.

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 sperm and elimination of bacteria following storage of extended semen in vitro. In Experiment 1, 7 antibiotics were compared: amikacin, gentamicin, streptomycin, potassium penicillin, sodium penicillin, ticarcillin, and polymixin B. In Experiment 2, 3 antibiotic treatments were compared: potassium penicillin G, amikacin, or a combination of potassium penicillin G and amikacin. In Experiment 3, 3 antibiotic treatments were compared: potassium penicillin G-amikacin, ceptiofur, and a combination of ticarcillin and clavulanic acid (Timentin). Control treatments (antibiotic-free extender) were included in each experiment. Six motility 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-line velocity. In Experiment 1, mean percentages of motile, progressively motile and rapidly motile sperm were lower (P < 0.05) in semen exposed 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 ticarcillin. Mean straight-line velocity of sperm in extender containing polymixin B was lower (P < 0.05) than that of all other treatments, with exception of control, streptomycin or ticarcillin. Semen samples containing gentamicin, amikacin, streptomycin, or potassium penicillin were more effective (P < 0.05) at eliminating bacterial growth than those samples containing polymixin B. Semen samples containing gentamicin were also more effective (P < 0.05) at eliminating bacterial growth than those samples containing ticarcillin or sodium penicillin. In Experiment 2, mean percentage of rapidly-motile sperm, and mean curvilinear, average-path, and straight-line velocities were greater (P < 0.05) for potassium penicillin-amikacin than values for all other treatments. In 2 of 3 stallions, an effect of treatment on percentage of motile sperm was detected (P < 0.05). For one stallion, mean motility of potassium penicillin-amikacin was greater (P < 0.05) than that of all other treatment groups. For another stallion, mean motility of the control was lower (P < 0.05) than that of the other treatments. Following storage, potassium penicillin (16/18 [89%]) or potassium penicillin-amikacin (17/19 [94%]) were more effective (P < 0.05) at controlling aerobic and anaerobic bacterial isolates in semen specimens than was amikacin (10/18 [56%]). In Experiment 3, a difference among treatment groups for motility variables was not detected (P < 0.05). No bacterial growth was recovered in antibiotic-treated semen, with exception of Micrococcus sp. (2 colonies) which were isolated from one semen specimen treated with ceptiofur.

Techniques for evaluating selected reproductive disorders of stallions

Numerous techniques may be used for evaluation of the different reproductive disorders of the stallion. Approaches may vary from real-time ultrasonography and biopsy for evaluating testicular tumors to use of special assays for evaluating sperm or plasma for presence of antisperm antibodies. This communication addresses techniques used to evaluate five relatively uncommon, but perplexing, disorders of breeding stallions: (1) seminal vesiculitis, (2) hemospermia associated with idiopathic urethral defects, (3) acrosomal dysfunction, (4) abnormal spermatozoal chromatin, and (5) azoospermia.