The effects of caffeine on the motility and viability of stallion spermatozoa at different temperature conditions.

The purpose of this study was to evaluate the dose- and time-dependent effect of caffeine treatment on the motility and viability of stallion spermatozoa at different temperatures. Six dose groups (A to F) were established with changing caffeine concentrations (from 0.625 to 10 mg/mL). The control samples were prepared by diluting the ejaculate only with physiological salt solution. The samples were examined after 0, 1, 2 and 3 h of incubation at 5 °C and 37 °C. The motility parameters were evaluated by Computer Assisted Semen Analyzer (CASA) system, and the viability was assessed by the mitochondrial toxicity test at the end of the incubation. A positive effect of the lowest tested caffeine concentration on the motility parameters was observed throughout the incubation period at 5 °C. At the end of the 3h incubation, the viability in every sample in these groups, treated with any caffeine concentration, showed lower values compared to the control. At the higher incubation temperature (37 °C), caffeine positively affected the motility in samples B (P < 0.05) and D, E, F (P < 0.001) after 3 h of incubation; however, the viability showed a slightly decreasing tendency. Our results suggest that caffeine, in an optimal concentration, may be used as a component of stallion semen extenders.