Date Full Report Received
Date Abstract Report Received
Funded ByNational Pork Board
Surgical castration is routinely performed on commercial pig farms in North America to prevent boar taint and aggression. This procedure is known to be painful for piglets, yet is typically done without the use of analgesics or topical anesthetics for pain relief. In Canada, the Code of Practice for the Care and Handling of Pigs was updated in 2014 and requires, as of July 1st, 2016, castration of piglets be done with analgesia to help control post-procedure pain. There is a lack of scientific data available regarding which drugs are effective in reducing pain in piglets, making it difficult for veterinarians to recommend specific drugs to producers. The objective of this research project was to determine whether castration and tail docking pain in piglets can be minimized or eliminated through the use of common analgesic (pain reducing) drugs, and if so, which drug(s) and dose is effective. We also developed a novel Piglet Grimace Scale (PGS) to be used as a tool to assess piglet pain and we sought to validate the scale as a replacement for the gold standard but highly time consuming behavioral scoring methods.
We used three measures to assess pain in piglets: behavior (both general piglet behavior and those specific to pain), piglet vocalization, and the PGS. We assessed two nonsteroidal, antiinflammatory drugs (NSAIDs), (meloxicam [Metacam®] and ketoprofen [Anafen®]), two opioids (butorphanol [Torbugesic®] and buprenorphine [Vetergesic®]) and several lidocaine-based topical anesthetic agents, including Maxilene 4®. These specific NSAIDs are licensed for use in swine in North America and are commonly used on pig farms to reduce pain in growing and mature animals. While lidocaine is licensed for food-producing animals, Maxilene 4®, an ‘over-the-counter’ topical agent, is not specifically licensed and opioids do not have label approval for use in any food-producing animal. Opioids are also controlled substances and can only be administered under direct veterinary supervision, thus the purpose of using opioids in this work was to develop a positive control for pain relief against which to measure the efficacy of other analgesic agents.
Several pilot trials were conducted to evaluate dose of NSAID, potential toxicity and pharmacokinetics and efficacy of topical anesthetic agents, to determine the best agents and doses to use in the subsequent definitive trials. Our first major trial assessed the effectiveness of meloxicam (0.4mg/kg and 1.0mg/kg) and ketoprofen (6.0mg/kg) when given intramuscularly to reduce pain in castrated piglets. A pilot study found 1.0mg/kg meloxicam (2.5x the label dose) was non-toxic and safe to administer to piglets. Based on behavioral and PGS results, we found that none of these NSAID treatments were effective in significantly reducing pain following castration. Piglets administered an NSAID demonstrated as many pain behaviors as piglets that were given nothing for pain relief. We also found that there was a significant increase in pain behaviors 24h post-castration, suggesting that castration pain persists long after the procedure occurs. The PGS results correlated well with pain behaviors.
Our second major trial assessed the effectiveness of buprenorphine (0.04mg/kg) and butorphanol (0.2mg/kg) when given intramuscularly to reduce pain and vocalizations of castrated piglets. The results of an initial pilot study suggested that butorphanol caused some piglets to become groggy (which might put them at risk of being crushed by the sow) and vomit, thus this drug was not used in further trials, whereas buprenorphine appeared to be well tolerated by the piglets. Based on behavioral analyses and the PGS, we found that buprenorphine was highly effective in reducing castration pain and facial grimacing of piglets, and caused no obvious side effects. From this study, we also found that low body weight piglets (i.e., runt piglets) grimace as much as a piglet in pain. Buprenorphine did not reduce high-frequency vocalizations at the time of castration.
Our third major trial assessed a multi-modal approach to pain management (meloxicam + buprenorphine + Maxilene 4®) in reducing pain and vocalizations of castrated piglets. Two pilot studies evaluating the effects of five topical anesthetic agents with or without NSAIDs suggested that, while not significant, application of Maxilene 4® led to a trend in reducing painful behavior in piglets post-castration, thus this compound was used for the definitive trials. In the definitive multimodal trial, it was determined that the use of buprenorphine alone was as efficacious as when NSAIDs (i.e., meloxicam) or topical anesthetics (Maxilene 4®) were added. Further, the single injection of buprenorphine 20min prior to surgical castration provided effective pain relief out to 24h. PGS results similarly matched behavioral scoring and vocalization results indicated that buprenorphine with or without other analgesics or topical anesthetics did not relieve pain associated with the actual castration event (similar to previous trials).
Tail docking studies in male and female piglets yielded similar results. Buprenorphine alone, administered I.M. 20min in advance of the procedure, was highly effective at alleviating pain following tail docking out to 24h. It did not alleviate the immediate pain associated with tail docking. Male and female piglets responded similarly to analgesics.
Overall, our findings indicate an NSAID (meloxicam, ketoprofen) or topical anesthetic alone are not enough to provide pain relief to piglets undergoing surgical castration. An opioid (buprenorphine) was highly effective at reducing surgical castration pain without any unwanted side effects, with a multi-modal approach to pain management (NSAID + opioid + topical anesthetic) being no more effective in reducing pain. Our detailed behavioral analyses suggest that a single injection of buprenorphine provides effective pain coverage out to 24h for both castration and tail docking procedures. While NSAID use may be the more practical option to satisfy this new legislation, current labelled NSAIDs are ineffective in addressing castration pain. As public concern for animal welfare in agriculture systems grows, it is of increasing importance that swine producers and veterinarians demonstrate that they are providing effective options for piglet well-being. We are hopeful the final results of this research project will allow more thorough recommendations for piglet pain control.