Vocal responses of piglets to castration: identifying procedural sources of pain

The aims of this study were to identify which aspects of castration are painful to piglets, and to determine if less painful methods are available. Previous work has shown that piglets produce more high frequency calls (>1kHz) when castrated than when handled identically but not castrated, or when castrated using a local anesthetic. In Experiment 1, we used 90 piglets to assess the vocal responses to different components of the castration procedure: restraint, washing the ano-genital region, scrotal incision, and pulling/severing of the spermatic cords. Compared to sham-operated animals (which were restrained and washed but not castrated) incision of the scrotum produced much more high-frequency calling than restraint alone at the same stage of the procedure. Pulling and severing the spermatic cords evoked the greatest amount of calling, significantly more than the incision, regardless of the order in which the incision and pull/sever were performed (P<0.001). In Experiment 2 (49 piglets), we found no difference in calling between two methods routinely used to sever the spermatic cord: cutting the cord with a scalpel versus tearing the cord by pulling on the testicle. These findings suggest that the pulling and severing of the spermatic cords are the most painful components of castration, yet altering the method of severing resulted in no change in call rate. Rather than focusing on pain control, welfare problems associated with castration may be better reduced by using non-surgical approaches, or by eliminating the need for castration in the first place.