Scientific Abstract

Castration occurs on commercial pig production farms to prevent the accumulation of boar taint and agonistic behaviors. Historically, neonates were believed incapable of experiencing pain because of their immature nervous system and lack of specific behavioral signs. However, current evidence demonstrates that neonates do in fact experience pain and if left untreated, can result in permanent neuroanatomic or behavioral changes. Thus, pain management is important for young animals.

Review of the literature revealed a variety of study designs and outcomes that are not always defined or collected in a similar manner which in turn makes evaluating efficacy of pain mitigation interventions difficult and has prevented consensus on best practices for pain relief. The protocol describes a methodology to directly or indirectly assess behavioral, physiological, and neuroendocrine changes in piglets associated with pain resulting from surgical castration. The information presented was compiled through an inclusive series of meetings that synthesized the best current understanding of researchers, veterinarians, industry, and regulatory agencies. It is further developed into a research protocol template, provided concurrently, to facilitate and guide comprehensive pain mitigation interventions for 3- to 5-day-old male piglets following surgical castration.

In brief, 4 treatment groups are recommended for the research protocol: (1) sham castration (SHAM), (2) sham castration with intervention (SHAM+TRT), (3) surgical castration with placebo control (CAST), and (4) surgical castration with intervention (CAST+TRT). For endpoint validation purposes, buprenorphine (0.04 mg/kg) administered intramuscularly prior to surgical castration will be used as a “gold standard” intervention as it has been found to significantly reduce surgical castration pain in 5-day old piglets. Piglet (within litter) is the experimental unit, and all treatments should be represented within a litter at least once. Treatments may be duplicated within a litter if there are additional male piglets in the litter.

Measurable outcomes were selected based on validity, reliability, and sensitivity with each categorized as either primary or secondary. Primary outcomes are directly related to clinical signs of pain as established in the published literature while secondary outcomes are either directly related to clinical signs of pain but not completely validated or are indirectly related to clinical signs of pain and lend support to the primary outcomes. Primary outcomes recommended are observation of pain behaviors, activity tracking, infrared thermography, and cortisol concentrations. Secondary measures recommended are stride length, blood biomarkers (including neuroendocrine, inflammatory, immunological, and stress response markers), piglet grimace scale, body weight, and mortality rate. The final protocol was developed for use to demonstrate efficacy which is one component of the US Food and Drug Administration’s approval process of a pain mitigation drug or other intervention.