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

This study explores the impact of lidocaine, a local anesthetic often used during routine castration in horses, on equine sperm physiology and characteristics of sperm found in the epididymis post-castration. Essentially, the researchers found that in concentrations higher than 100μg/ml, lidocaine reduced some sperm motility parameters, but did not significantly affect the sperm’s morphology or overall functioning following epididymal flush post-castration.

Research Methodology

The study was divided into two separate experiments.

• In the first experiment, sperm was collected from four stallions and mixed with varying concentrations of lidocaine (ranging from 1 μg/ml to 10,000 μg/ml). Morphology and membrane integrity were assessed at the outset and 48 hours later. The researchers also studied sperm motility parameters such as total motility (TM), progressive motility (PM), velocity of average path (VAP), velocity of a curved line (VCL), and linearity (LIN) at multiple time points over a 48-hour period.
• In the second experiment, 12 stallions were castrated under general anesthesia. One testicle was removed without using intra-testicular lidocaine, while the other was removed 10 minutes after injecting 10 ml of 2% lidocaine. The aim was to compare the characteristics of the epididymal spermatozoa under these two conditions.

Key Findings

In the first experiment, lidocaine concentrations of 1 μg/ml or 10 μg/ml showed no significant difference in sperm characteristics or motility compared to the control group. With much higher lidocaine concentrations (100-10,000 μg/ml), certain motility parameters like PM, VAP, VCL, and LIN decreased substantially, as did TM in concentrations of 1,000-10,000 μg/ml. However, the sperm morphology remained unchanged across all lidocaine concentrations. Membrane integrity was noticeably affected only at the highest concentration of 10,000 μg/ml lidocaine.

In the second experiment, the researchers found lidocaine present in the epididymal flush of stallions treated with the anesthetic. However, no significant differences were observed in any measured parameters between the control and lidocaine-treated testicles. This indicates that the administration of intra-testicular lidocaine at the time of castration did not noticeably affect sperm characteristics following epididymal flushing.

Research Significance

The results of this study provide important insights about the effects of lidocaine on equine spermatozoa, especially in a clinical, in-vitro setting. The findings suggest that while lidocaine can inhibit certain motility parameters of sperm at higher concentrations, it does not seem to significantly affect the functionality or morphology of the sperm, nor does it affect sperm characteristics following epididymal flushing post-castration. This implies that the use of lidocaine during castration does not have a detrimental effect on sperm recovered post-castration, which may have potential use in breeding programs.