Effect of local anesthetic (lidocaine) on the quality of semen collected from the testicles of castrated stallions (15-32)


Jenny Boye, DVM, DACT (Resident)
Bruce Christensen, DVM, MS, DACT (Mentor)

Sperm from castrated horses can be saved if the testicles and epididymides (ducts that help to store sperm) are processed after they are removed from the stallion. During this procedure, the sperm is frozen and stored for future insemination. Castration surgery can be performed with or without the local pain medicine injected into the testicles when the horse is under general anesthesia. Lidocaine is the most commonly used drug for local pain relief during castration. The standard dose typically used in a routine castration is 10mls of Lidocaine 2% in each testicle.

If the sperm is to be harvested, however, the castration is often performed without lidocaine due to concern that the local pain medicine may affect the sperm quality. There is, however, no published evidence that shows any effect of lidocaine on equine sperm quality, fertility, or demonstrates actual contact between the lidocaine and the sperm. The project sought to determine the effect of lidocaine exposure on sperm quality, determine if there are measurable amounts of lidocaine in the sperm, when the lidocaine is injected into the testicles, and determine what the amount is; and determine if castration with lidocaine affects quality of sperm saved from the epididymis after castration, freezing and thawing.


During the in-vitro study, there was no significant difference for any of the measured motility parameters for lidocaine concentrations at low concentrations (1-10 μg/ml) compared with the lidocaine-free control sample. There were significant decreases in motility parameters in samples with high and very high lidocaine concentrations (100 μg/ml - 10,000 μg/ml) compared to the lidocaine-free control sample. Morphology was not affected by lidocaine at any concentration and membrane permeability was only affected at the highest concentration of lidocaine (10,000 μg/ml).

After castration, an average concentration of 1.027 ± 0.422 μg /ml lidocaine was detected in the epididymal flush of stallions treated with lidocaine during surgery. There was no effect on sperm quality parameters in sperm obtained from testicles with the use of lidocaine compared with the ones without the lidocaine during castration.

Based on these results, it should be considered safe to castrate a stallion with local anesthesia injected into the testicle before castration if an epididymal flush is intended post-castration. This would allow veterinarians to perform castrations with lower levels of pain as well as reducing the need for higher amounts of general anesthetic and pain medication post-surgery.