Efficacy of buprenorphine for management of surgical castration pain in piglets

Abstract

BackgroundSurgical castration is a painful procedure, performed routinely on commercial pig farms to prevent boar taint and reduce aggression. The objectives of this study were to assess the efficacy of 0.04 mg/kg buprenorphine (BUP) in reducing pain in castrated piglets, using behavioral indicators and vocalization analysis. This study also sought to further validate the Piglet Grimace Scale (PGS) as a pain assessment tool.A pilot study first assessed the safety of BUP or 0.2 mg/kg butorphanol administration to piglets (n = 4 per treatment). When no side effects were noted with BUP, ten litters of 5-day old piglets (n = 60 total, 15 per treatment group) were used, and randomly assigned to one of four possible treatments: BUP (castrated or uncastrated), saline, or sham. Treatments were administered as an intramuscular injection 20 min prior to surgical castration. Piglets were video recorded 1 h pre-procedure, post-castration for 8 h and for another hour, 24 h post-procedure. Behaviors were scored continuously for the first 15 min of each hour and 511 still-images of piglet faces were scored using the PGS. Vocalizations were recorded from each piglet at three points in the study: at initial handling, injection, and castration.ResultsButorphanol caused some piglets to become groggy and vomit and was not further evaluated. BUP-castrated piglets demonstrated significantly fewer pain behaviors and less facial grimacing compared to saline-treated pigs (P < 0.0001 and P = 0.0073, respectively). There was no difference between the pain behaviours displayed by BUP-castrated piglets compared to BUP-uncastrated and sham piglets (P = 0.9986 and P = 0.7484). There was also no difference in PGS score between BUP-castrated and BUP-uncastrated piglets (P = 0.9376). Piglets in the BUP-castrated group produced vocalizations of similar frequency, amplitude, power, and energy to saline-treated piglets.ConclusionsBuprenorphine was highly effective in alleviating castration-associated pain behaviors and facial grimacing in piglets, without causing any obvious side effects. Its administration did not reduce piglet vocalizations at the time of castration. The PGS corresponded well to piglet pain behaviors and has utility as a pain assessment tool.

Is the Piglet Grimace Scale (PGS) a Useful Welfare Indicator to Assess Pain after Cryptorchidectomy in Growing Pigs?

“…There is a lack of repeatability in stress/fear/pain studies in domestic animals, including pigs [35], in which case the absence of a clear pain assessment tool applicable across pigs of different age and weight arguably factors in. Existing literature reported results from experiments on 5-day-old piglets [9,11,12], minipigs [36], or straight-eared cross-breeds [37]. The original PGS describes the FAU "ear position" as "the ears are drawn back from forward (baseline) position" [12]; however, our observations failed to record unequivocal backward ear movements, which could be explained by the conformation of our older pigs.…”

Optimal Methods of Documenting Analgesic Efficacy in Neonatal Piglets Undergoing Castration

“…Little or no difference in pain-related behaviour was seen after castration performed with or without general anaesthesia [23,46]. This is not unexpected, notable that no significant differences in "pain-specific" behaviours between castrated and shamhandled neonatal piglets were evident in the first 2 hrs following castration in trials using videorecording techniques [54,57] as opposed to those using direct observation [28,44,65,68]. Data from these trials suggest that video-recording techniques may have high sensitivity to detect tail-wagging, however, lower sensitivity to detect other "pain-specific" behaviours such as tremors, spasms, huddling up, prostration or stiffness in neonatal piglets.…”

“…Vocalisation responses were also used to compare the castration procedure itself with cutting or tearing of the spermatic cord found to have little difference on the duration of responses [64]. Interestingly, intra-muscular injection of analgesics induces vocalisations of similar power (dB), frequency (Hz) and energy as that induced by pulling and tearing the spermatic cords during castration, and of significantly greater power (dB), frequency (Hz) and energy than skin incision [54].…”

“…Although the majority of these behaviours are short-lived (i.e. observed with the greatest frequency in the first 30 min to 1 hr following castration), some particular behaviours such as increased tail wagging and/or scratching tend to develop later in the postoperative period and have been observed to be increased for up to 2-5 days post-procedure in some studies [54,57], although not in others [24,68]. Overall in review, when comparing castrated piglets with sham handled controls, variation in general postures and non-specific behaviours have been marginal and/or conflicting, and are generally not considered reliable indicators of piglet pain [24,65].…”

“…These include; (a) physiological responses during the procedure [22,24,27,28,[33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][64][65][66][67][68][74][75][76][77][78], (b) nociceptive motor responses during the procedure [27,28,31,47,49,50,64,74]; (c) vocal responses during the procedure [22,[24][25][26][27][28]31,46,[50][51][52][53][54]...…”