The Use of Ceftiofur Sodium in the Extension and Cooled Storage of Equine Semen: Its Effects on Motion Characteristics, pH, Osmolality, and Bacterial Growth

During semen collection in the stallion, contamination of the ejaculate occurs secondarily to the normal microflora present on the external genitalia. These bacteria and their metabolites can negatively affect spermatozoal motility and viability during cooled storage. Therefore, the addition of antibiotics to the semen extender is warranted to reduce bacterial load and prevent further growth. Naxcel?? (ceftiofur sodium, Pfizer Inc., New York, NY) is a third generation cephalosporin antibiotic with high antibacterial activity and a broad resistance to ??-lactamases. The purpose of the current study was to evaluate varying levels of ceftiofur sodium added to a skim milk-glucose based semen extender in comparison to control (antibiotic-free extender) and other commonly utilized antibiotics on spermatozoal motion characteristics, semen osmolality and pH, and bacterial growth during cooled storage for 48 hours. Semen was collected and pH measurement, osmolality measurement, and aerobic culture were undertaken for each ejaculate (total of thirteen from three stallions). Each ejaculate was then divided and extended in a skim milk-glucose based semen extender (Har-VetTM Semen Extender, Har-VetTM, Spring Valley, WI) without antibiotic (control) or with one of seven different antibiotic groups: ceftiofur sodium at 250??g/ml (CEFT250); ceftiofur sodium at 500??g/ml (CEFT500); ceftiofur sodium at 1,000??g/ml (CEFT1000); ceftiofur sodium at 2,500??g/ml (CEFT2500); combination of amikacin sulfate and potassium penicillin G at 1,000??g/ml and 1,000IU/ml, respectively (AMKPCN); gentamicin sulfate at 1,000??g/ml (GENT); and ticarcillin disodium at 1,000??g/ml (TICAR). Extended semen was cooled and stored in a semen-transport container (EquitainerTM, Hamilton Research Inc, South Hamilton, MA) at approximately 5??C. Motility measures using computer-assisted semen analysis, pH measurements, and osmolality measurements were performed at 0, 24, and 48 hours after collection. Aerobic culture was performed for the eight extended groups after 24 and 48 hours of storage. Motion characteristics measured included: total motility (MOT), progressive motility (PM), curvilinear distance (DCL), average path distance (DAP), straight line distance (DSL), curvilinear velocity (VCL), average path velocity (VAP), straight line velocity (VSL), linearity (LIN), straightness (STR), wobble (WOB), beat cross frequency (BCF), and amplitude of lateral head displacement (ALH). Ceftiofur sodium had a dose-dependent effect on DCL, VCL, and ALH, with higher concentrations (1,000??g/ml and 2,500??g/ml) yielding increased values in comparison to controls (F test, P<0.05; post-test comparison, P<0.0071). There was also a significant effect of extender on STR (F test, P<0.05) with higher concentrations of ceftiofur sodium tending to decrease values in comparison to controls (P<0.028). The changes in motion characteristics are consistent with a trend toward spermatozoal hyperactivation. Stepwise, multiple regression analysis revealed pH was the strongest indicator for the increased motion characteristics, but it was only a minor predictor. There was no significant effect of extender noted for MOT, PM, DAP, DSL, VAP, VSL, LIN, WOB, and BCF. There was an effect of time on MOT and PM with parameters decreasing significantly over time (F test, P<0.05). Time also had an effect on DAP, DSL, VAP, VSL, LIN, STR, and WOB (F test, P<0.05) with most values decreased significantly after 48 hours of storage. There was a significant effect of extender group on pH (F test, P