Towards Objective Assessment of Analgesia for Surgical Castration, By Dr. Brad DeWolf from South West Ontario Veterinary Services,

Regulation with respect to piglet castration in Europe has gradually increased over the last decade. The marketing of entire males or the use of immunocastration have offered an alternative to surgical castration. Some countries have been slow to adopt any of these new technologies and many deadlines for change have come and gone with some countries showing little change in production practices. In some countries where surgical castration is still the main method for controlling boar taint there has been an adoption of requirements for increased use of analgesics. As of Jan. 1 2021 , Germany has moved beyond just analgesia and now requires the use of general anaesthesia for surgical castration. In Canada, although we have adopted the use of analgesics for castration it could be argued  that analgesia means less pain but not no pain.

As the discussion continues as to what is right for the pig continues it will become increasingly important to have reliable and repeatable methods for objectively quantifying levels of pain in piglets during and after surgical castration. These University of Minnesota researchers wanted to study the assessment of acute pain in piglets during castration by using  behavioral indicators. Piglets (n=88) were randomly allocated to one of two treatments: surgical castration and sham-castration. Within 24 hours after birth, identical castration procedures were followed for both treatment groups, except sham piglets were not castrated. Struggle behavior (curl ups, leg kicks, and body flailing) and vocalization (duration and peak frequency) were analyzed during the castration procedure.

The researchers found the following:

  • Castrated piglets kicked more frequently than sham piglets (28.8 vs. 21.3 kicks/min, SE = 0.09; P = 0.02).
  • Castrated piglets displayed body flailing more frequently than sham piglets ( 51.2% vs 4.4% ; P = 0.03).
  • Castrated piglets responded with more high frequency (≥1,000 Hz) calls than sham piglets (23.6 vs. 18.6 calls/min, SE = 0.26; P = 0.04)
  • Castrated piglets responded with high frequency calls for a longer duration than sham piglets  (0.45 vs. 0.27 sec/call, SE = 0.04; P = 0.08).

Take Home Messages:

  • The results indicate that surgical castration without analgesia increased the frequency of leg kicks, body flailing, and high frequency calls compared to sham-castration.
  • These findings should not be a surprise to anyone but the importance of these findings is that there continues to be a growing body of evidence for the use of behavioural markers for assessing the “effectiveness” or lack therof of our analgesic interventions. Efficacy could be related to the analgesic properties itself or it could be related to how they are administered in a production setting.
  • How will our pain control interventions be perceived in the future? “ The proof of the pudding is in the eating”

Ref: Maria Lou , Beth Ventura , John Deen , Yuzhi Li   Surgical Castration Changes Struggle Behavior and Vocalizations in Male Piglets  J Appl Anim Welf Sci . 2021 Apr 16;1-8. doi: 10.1080/10888705.2021.1916938. Online ahead of print.