Does Injection Site or Time From Injection of Local Anaesthetic To Castration Reduce Castration Pain? By Dr. Brad DeWolf from South West Ontario Veterinary Services

Surgical castration of piglets continues to be “under the microscope” with respect to animal welfare. Some countries such as Denmark allow surgical castration when a local anaesthetic such as procaine is used as a local anaesthetic. These Danish researchers reported the results of a study that looked at the efficacy and side effects of various volumes of procaine that could be injected into the testicle. This same group of researchers wanted to further investigate the effectiveness of two very specific local anaesthetic injection locations. Intra-funicular and intra-testicular injection of procaine were compared. Intrafunicular injection involves an injection into the spermatic cord or “ funiculus spermaticus” . This is the tubular structure containing vas deferens, arteries, veins and nerves that descend to the testes. It is easier to target the testes for injection but the researchers wanted to know if an injection directly into the spermatic cord would provide improved local anaesthesia for surgical castration. The researchers also wanted to study the impact of various strategies of waiting time between injection and castration. The four time intervals between anaesthetic injection and castration were 2.5, 5, 10, and 30 min. The study involved 597 3 to 4 day old male piglets. The treatments included surgical castration without anesthesia , local anesthesia followed by castration involving all combinations of injection method and interval. As a control they also did “sham handling” separated by the same four intervals. Responses of piglets to drug injection, castration and sham handling were evaluated based on quantification of intra-procedural vocalizations, leg movements and saliva cortisol concentration in samples taken before and after treatments.

The researchers found the following:

  • No differences were found between intrafunicular (spermatic cord) and the simpler intratesticular injection method.
  • Intervals of 2.5 or 30 min led to stronger piglet responses than the other intervals of 5 and 10 minutes.
  • Treatments involving injecting the local anesthetic as well as castration led to significantly stronger responses than sham handling alone. ( No surprise there.)
  • All treatments including sham handling (no injection or castration) led to a significant increase in saliva cortisol with no differences between anesthesia treatments and controls.

Take Home Messages

  • The researchers concluded that castration 5 to 10 min after intra-testicular injection of procaine seems to be the preferred timing.
  • Saliva cortisol was not a very useful tool for parsing out the welfare differences between the various local anaesthetic techniques. This confirms a similar finding in previous research.
  • The researchers further suggested that the overall benefits of injectable local anaesthetic for castration were arguable. Castration with local anaesthesia offers some reduction of pain but does  not eliminate the pain associated with either injection or castration.

Ref: Mathilde Coutant , Jens Malmkvist , Marianne Kaiser , Leslie Foldager , Mette S Herskin  Piglets’ acute responses to local anesthetic injection and surgical castration: Effects of the injection method and interval between injection and castration  Front Vet Sci . 2022 Sep 29;9:1009858. doi: 10.3389/fvets.2022.1009858. eCollection 2022.