Effects of lidocaine on equine ejaculated sperm and epididymal sperm post-castration

In equids, it is common to inject lidocaine into the testicles at the time of routine castration to provide analgesia. The effects of lidocaine on equine sperm have not been evaluated in vitro or on epididymal sperm collected following castration. The aims of this study were to determine effects of clinically relevant doses of lidocaine on equine spermatozoa in vitro using freshly collected semen and to compare the characteristics of epididymal spermatozoa after routine castration with or without intra-testicular lidocaine administration. We hypothesized that increasing concentrations of lidocaine would decrease total motility (TM), progressive motility (PM), velocity of the average path (VAP), velocity of the curved line (VCL), linearity (LIN), normal morphology (M) and membrane integrity (MI). We also hypothesized that injection of intra-testicular lidocaine would decrease TM, PM, VAP, VCL, LIN, M, and MI following routine castration, epididymal flushing and cryopreservation. In experiment 1, sperm was collected from four stallions and mixed with lidocaine at concentrations of 1 μg/ml, 10 μg/ml, 100 μg/ml, 1,000 μg/ml and 10,000 μg/ml. M and MI were compared to the control sample at 0 and 48 h. Motility parameters were analyzed at 0, 2, 4, 6, 24, and 48 h. In experiment 2, 12 stallions were castrated under general anesthesia. One testicle was removed without the use of intra-testicular lidocaine and the other testicle was removed 10 min after injection of 10 ml of 2% lidocaine. Results: In experiment 1, fresh sperm showed no significant difference (p < 0.05) compared to control at either 1 μg/ml or 10 μg/ml concentrations of lidocaine. There were significant decreases in PM, VAP, VCL, and LIN at concentrations of 100μg/ml-10,000 μg/ml and for TM at lidocaine concentrations of 1,000-10,000 μg/ml compared to control. Morphology did not change at any lidocaine concentration. Membrane integrity decreased significantly at 10,000 μg/ml lidocaine. In the second experiment 1.03 ± 0.42 μg/ml lidocaine was detected in the epididymal flush of stallions treated with lidocaine. There were no significant differences in any measured parameters between the control and the lidocaine treated testicles. Intra-testicular lidocaine injection at the time of castration did not affect any measured parameters after epididymal flush. Lidocaine concentrations higher than 100 μg/ml in-vitro resulted in decreased motility parameters of the spermatozoa independent of exposure time.