The addition of ticarcillin-clavulanic acid to INRA 96 extender for stallion semen cooling.

Reasons for performing study: A commonly used commercial extender (i.e. INRA 96) contains antimicrobials that may have limited effectiveness. Therefore, addition of ticarcillin-clavulanic acid to this extender is a widespread procedure in the equine breeding industry in the United States. However, such practice has not been critically evaluated.

Objectives: To evaluate the addition of ticarcillin-clavulanic acid to INRA 96 and different extender and antimicrobial storage conditions on sperm function and antimicrobial effectiveness.

Methods: Gel-free semen (42 ejaculates from 14 mature Quarter Horse stallions) was extended with INRA 96 and stored for 24 h in an Equitainer II. The effects of added ticarcillin-clavulanic acid and different extender storage procedures on sperm motion characteristics (by computer-assisted analysis), sperm membrane integrity (by fluorescence-based measurement) and suppression of bacterial growth (by aerobic and anaerobic culture methods) were evaluated using analysis-of-variance and Chi-square statistical methods. The P value for significance was set at < 0.05.

Results: Freezing and thawing of modified or unmodified extender prior to use for stallion semen resulted in reduced sperm quality post cooling for 24 h, as evidenced by a significant reduction in sperm motility (i.e. total and progressive) and sperm membrane integrity. Addition of ticarcillin-clavulanic acid to extender resulted in higher sperm velocity when the reconstituted antimicrobial was subjected to cooled storage, as compared with frozen storage, prior to use. Only 28 of 42 ejaculates (67%) yielded presence of bacteria in neat semen but addition of ticarcillin-clavulanic acid to INRA 96 was not different than INRA 96 alone for inhibiting growth of bacteria (98 vs. 94%, respectively).

Conclusions: Addition of ticarcillin-clavulanic acid (1 mg/ml) to INRA 96 did not adversely affect sperm quality in extended semen after cooled storage. Extender freezing and thawing prior to use had detrimental effects on sperm quality.

Potential relevance: These data suggest that INRA 96 should not be frozen and thawed prior to use. Addition of ticarcillin-clavulanic acid to INRA 96 did not impair sperm quality. All extender treatments effectively controlled the bacterial growth compared with neat semen.