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Castration is a painful procedure performed in swine and to date, there are no approved products available in the US to alleviate this pain. Previous work evaluating the efficacy of flunixin meglumine has shown promise in mitigating pain in swine, but no work to date has evaluated transdermal flunixin efficacy in mitigating castration pain in piglets. Therefore, the objective of this study was to evaluate the efficacy of transdermal flunixin (TDF) in mitigating castration pain utilizing a previously validated behavioral pain scale. A total of 98 Large White x Duroc cross male piglets from 98 litters were enrolled in this study. Piglets were randomly assigned to the following treatments: transdermal flunixin plus castration (3.33 mg/kg; n = 24), transdermal flunixin plus sham castration (3.33 mg/kg; n = 26), topical physiological saline plus sham castration (n = 24), or topical physiological saline plus castration (n = 24). All treatments were administered 24 h prior to castration. Four-minute continuous video clips were collected 24 hours before castration, immediately post-castration, and 24 hours post-castration. Video clips were then observed and scored by one trained observer using a 4-point pain scale (score 0–3) encompassing the five behavioral domains of the pig acute pain scale (UPAPS). Total pain score averages were analyzed as repeated measures by analysis of variance applying a multilevel model.
The UPAPS effectively distinguished varying levels of painful and non-painful states in castrated piglets as observed via deviations in total pain scores across timepoints, treatment, and treatment*timepoint. Immediately post-castration, piglets in the topical physiological saline plus castration and transdermal flunixin plus castration group demonstrated greater total average pain scores than piglets in the topical physiological saline plus sham castration and transdermal flunixin plus sham castration groups and castrated piglets treated with transdermal flunixin demonstrated lower total pain scores and required less analgesic intervention immediately post-castration compared to castrated piglets receiving no treatment. For topical physiological saline plus castration group 54% required rescue analgesia compared to 29%, 8%, and 0% for transdermal flunixin plus castration, transdermal flunixin plus sham castration, and topical physiological saline plus sham castration piglets respectively.
Future work should evaluate the implementation of this pain management protocol on a wide scale commercial farm setting.
Lopez-Soriano M, Rocha Merenda V, Esteves Trindade PH, Loureiro Luna SP, Pairis-Garcia MD. Efficacy of transdermal flunixin in mitigating castration pain in piglets. Frontiers in Pain Research. 2022; 3. https://www.frontiersin.org/articles/10.3389/fpain.2022.1056492
