Local Anesthesia in Piglets Undergoing Castration—A Comparative Study to Investigate the Analgesic Effects of Four Local Anesthetics Based on Defensive Behavior and Side Effects

SIMPLE SUMMARY: More than 80 million male piglets are castrated every year within the first week of life mostly without pain relief in the EU. Castration is performed to prevent boar taint, to minimize aggressive and sexual behavior associated with intact males and to gain a constant quality of meat. It is an important animal welfare issue to eliminate pain caused by castration. Local anesthesia, meaning the sole injection of a local anesthetic into the testicles and in the surrounding tissue of conscious piglets, prior to castration is a currently discussed method in Germany. Thus, it was the aim of the present study to investigate the effect of four local anesthetics (procaine, lidocaine, bupivacaine and mepivacaine) on pain relief during surgical castration in conscious piglets. To assess pain, defensive behavior of piglets undergoing injection and castration was evaluated. In addition, attention was paid to possible side effects. Considering healing, bleeding and weight gain no negative impacts were observed, but impairments of locomotor activity occurred. The results indicate that lidocaine and mepivacaine are able to achieve significant pain relief during the castration procedure, whereas procaine and bupivacaine only during the severing of the spermatic cord. ABSTRACT: The aim of the present study was to investigate the effect of four local anesthetics on pain relief during surgical castration under standardized conditions in conscious piglets. Therefore, 71 male piglets (three to seven days) were distributed into control groups (handling, castration without anesthesia or analgesia) and local anesthetic trial groups (procaine, lidocaine, bupivacaine, mepivacaine). Then, 20 min prior to castration, animals of the treatment groups, except piglets in the handling group, received an injection of a local anesthetic or sodium chloride of 0.5 mL intratesticularly and 0.5 mL subscrotally. During injection and castration, defensive behavior was evaluated. Locomotor activity, as well as postoperative bleeding, wound healing and average daily weight gain were assessed to detect side effects. The injection caused increased defensive movements, significantly in the bupivacaine group. Lidocaine and mepivacaine significantly reduced defensive movements during castration, and procaine and bupivacaine only during severing of the spermatic cord. Impairments of locomotor activity were found in piglets injected with lidocaine, bupivacaine or sodium chloride. Considering healing, bleeding and weight gain, no negative impacts were observed. In conclusion, lidocaine and mepivacaine were able to achieve significant pain relief during the castration procedure, whereas procaine and bupivacaine only during the severing of the spermatic cord. Moreover, the injection of bupivacaine seemed to be painful itself.