Part I: understanding pain in pigs—basic knowledge about pain assessment, measures and therapy

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Kschonek et al. Porcine Health Management (2025) 11:12 Porcine Health Management https://doi.org/10.1186/s40813-025-00421-0 REVIEW Open Access Part I: understanding pain in pigs—basic knowledge about pain assessment, measures and therapy Julia Kschonek1*, Lara Twele2, Kathrin Deters3, Moana Miller4, Jennifer Reinmold3, Ilka Emmerich5, Isabel Hennig‑Pauka3, Nicole Kemper4, Lothar Kreienbrock1, Michael Wendt6, Sabine Kästner7 and Elisabeth grosse Beilage3 Abstract Background Pigs can suffer from pain due to spontaneously occurring diseases, wounds, injuries, trauma, and physi‑ ological conditions such as the farrowing process; however, this pain is often neglected. To increase knowledge and awareness about this phenomenon, the current article presents a scoping review of basic and new approaches for identifying, evaluating, and treating pain in pigs. Methods A scoping review was conducted with results from a search of the electronic database VetSearch and CABI. With regard to eligibility criteria, 49 out of 725 publications between 2015 and the end of March 2023 were included. The findings are narratively synthesized and reported orienting on the PRISMA ScR guideline. Results The results of this review showed that practitioners need to consider pain not only as a sign of a disease but also as a critical aspect of welfare. If both the symptoms of pain and the underlying reasons remain unassessed, the longevity and prosperity of pigs may be at risk. In this respect, veterinarians are obliged to know about intricacies of pain and pain mechanisms and to provide adequate treatment for their patients. Conclusion It is pivotal to increase knowledge about pain mechanisms, the reasons for heterogeneity in behav‑ ioural signs of pain, and methods for evaluating whether a

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ivotal to increase knowledge about pain mechanisms, the reasons for heterogeneity in behav‑ ioural signs of pain, and methods for evaluating whether a pig is experiencing pain. This article will help practitioners update their knowledge of this topic and discuss the implications for everyday practice. Keywords Nociception, Inflammatory pain, Neuropathic pain, Clinical pain, Pain parameters, Pain therapy 6 *Correspondence: Clinic for Swine and Small Ruminants, Forensic Medicine Julia Kschonek and Ambulatory Service, University of Veterinary Medicine, Foundation, julia.dorothee.kschonek@tiho-hannover.de Hannover, Bischofsholer Damm 15, 30173 Hannover, Germany 1 7 Institute for Biometry, Epidemiology and Information Processing (IBEI), Clinic for Small Animals, University of Veterinary Medicine, Foundation, University of Veterinary Medicine, Foundation, Hannover, Bünteweg 2, Hannover, Bünteweg 2, 30559 Hannover, Germany 30559 Hannover, Germany 2 Clinic for Horses, University of Veterinary Medicine, Foundation, Hannover, Bünteweg 9, 30559 Hannover, Germany 3 Field Station for Epidemiology, University of Veterinary Medicine, Foundation, Hannover, Büscheler Str. 9, 49456 Bakum, Germany 4 Institute for Animal Hygiene, Animal Welfare and Farm Animal Behavior, University of Veterinary Medicine, Foundation, Hannover, Bischofsholer Damm 15, 30173 Hannover, Germany 5 Institute of Pharmacology, Pharmacy and Toxicology, Faculty of Veterinary Medicine, University Leipzig, An den Tierkliniken 39, 04103 Leipzig, Germany © The Author(s) 2025. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the

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License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creativecom‑ mons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data. Kschonek et al. Porcine Health Management (2025) 11:12 Page 2 of 18 Introduction which are injured or have a disease associated with severe Untreated pain in animals is associated with suffering, pain or suffering and where there is no other practical distress and detrimental effects on physical and men- possibility to alleviate this pain or suffering” [15]. tal health and thus represents a welfare-related concern In summary, the identification and evaluation of pain [1]. The causes and indicators of pain are less examined in pigs is pivotal for ensuring the welfare and prosperity in pigs than in companion animals [2], and pain manage- of pigs and for deciding about timely euthanasia in severe ment in pigs is often disregarded in textbooks [3]. Indeed, cases. To support these pivotal processes, this article

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about timely euthanasia in severe ment in pigs is often disregarded in textbooks [3]. Indeed, cases. To support these pivotal processes, this article pigs are still among the most neglected livestock species summarizes the knowledge and understanding of pain in terms of pain assessment and treatment [4]. Although and related mechanisms. This article is a starting point some related studies have been published, the focus is for readers to become familiar with pain research and often limited to certain topics. For example, publications pain in pigs (Part I). Moreover, findings from the latest examining pain assessment have focused on pain man- publications are presented to suggest how daily practice agement procedures (surgical castration, tail docking, can benefit from findings in research. Building upon this teeth grinding, ear tagging or notching). Other studies review, another article addresses the state of knowledge have focused on pigs that are used as laboratory animals on pain in specific, spontaneously occurring diseases and in translational medicine [5–11]. This is likely due to the injuries in pigs (Part II). critical discussion on the necessity of husbandry and laboratory procedures. However, despite being a serious Method for the review welfare concern, pain caused by spontaneously occur- The aim of this scoping review is to enhance the under- ring diseases or injuries including, wounds, trauma and standing of pain and related mechanisms in pigs. In addi- physiological conditions like neuroma among pigs has tion to summarizing the basic literature on the subject, been less well examined and reported [3, 11, 12]. The rea- topics and new approaches to assess pain in pigs were son for this difference may be that pain directly induced examined in studies

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11, 12]. The rea- topics and new approaches to assess pain in pigs were son for this difference may be that pain directly induced examined in studies published between 2015 and the by human intervention gains more attention than pain end of March 2023. This scoping review was conducted resulting from spontaneously occurring diseases or inju- in accordance with the PRISMA-ScR reporting guideline ries. Another reason may be that veterinarians need to [16]. learn giving more consideration to pain management, as The search database “VetSearch” (EBSCOhost Research shown by a survey of veterinarians’ use of analgesics in Database) was used which includes the following data- livestock animals [13]. In general, it is the responsibility bases: CAB Abstracts 1990-Present, Tierärztliche Hoch- of a veterinarian to try to successfully alleviate pain in schule Hannover Catalogue, CAB Abstracts, CAB the animals under care [2]; however, achieving this goal Abstracts Archive, eBook Collection (EBSCOhost), can be complicated by difficulties associated with iden- ERIC, E-Journals, OpenDissertations, MEDLINE, and tifying pain. The identification and grading of pain needs Global Health. Thus, studies from key publishers (such as to be a necessary part of clinical examinations of individ- Wiley, Springer, Wiley-Blackwell, Taylor & Francis, Else- ual pigs. However, clinical examinations often focus on vier, and MDPI Biomedical Central Ltd., Cambridge Uni- aetiological diagnoses, while the role or presence of dis- versity Press, among others) were included and addressed ease-related pain is not always of concern. Consequently, with the help of one single interface (one search mask). therapy often aims to resolve the cause of the disease and To control the search process and adhere to

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help of one single interface (one search mask). therapy often aims to resolve the cause of the disease and To control the search process and adhere to the journal neglects to treat the related pain. requirements, we iterated the research steps in the Cabi For several reasons, it is important for a veterinary Rxiv database in the English language. practitioner to be able to identify pain as an impor- To find appropriate publications, two alternate search tant symptom in pigs, thus enabling the veterinarians to strings were used. Findings for the first search string are choose an appropriate therapy and to monitor the effec- called version 1 (V1) for results of the search in VetSearch tiveness of the therapy. In the role of an advisor, for exam- and version 3 (V3) for CABI Rxiv. Findings for the second ple, a veterinarian must support farmers in discharging search string are called version 2 (V2) for results of the their responsibility to protect their pigs from unnec- search in VetSearch and version 4 (V4) for CABI Rxiv. essary pain and suffering [14]. Moreover, severe pain, The following search terms were used: (“pain”) in title which cannot be effectively treated, is a common reason (V1, V3) or keywords (V2, V4) AND in text ("pig" OR for euthanasia or emergency killing of a pig in practice. "pigs" OR "hog" OR "hogs" OR "porcine" OR "swine" OR In this respect, thoroughly assessing the animal for the "boars" OR "boar" OR "sow" OR "sows" OR "piglet" OR presence of possible pain states ensure that the correct "piglets" OR "weaner" OR "weaners") AND in text ("noci- approach is selected in jurisdictional terms, where emer- cept*" OR "hurt*" OR "suffer*" OR "damag*" OR in text gency killing is defined as “[…] the killing of animals Kschonek et al. Porcine Health

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ere emer- cept*" OR "hurt*" OR "suffer*" OR "damag*" OR in text gency killing is defined as “[…] the killing of animals Kschonek et al. Porcine Health Management (2025) 11:12 Page 3 of 18 "injur*" OR "defect*" OR "harm" OR "sensation" OR "bur- with, or resembling that associated with, actual or poten- den" OR "sensorium") AND NOT in text (“patients”). tial tissue damage.” ([18], Text Box 2). While the IASP In brief, 715 publications were found. For the first explicitly addresses the pain experience of animals now, screening step, the list of retrieved publications was earlier definitions emphasized the focus on the animals’ assessed online (title, author, abstract) or downloaded response to pain: … [pain] changes the animal’s physi- and an overview of topics was generated, (the topics cor- ology and behaviour to reduce or avoid the damage, respond to the chapters of the manuscript nociception, to reduce the likelihood of recurrence and to promote inflammation, therapy (non-husbandry interventions; recovery…” ([19], p.266). A key aspect to bear in mind, in husbandry interventions), neuropathic pain and assess- this respect, is that the inability to communicate the pain ment, other animals or topics). Papers were considered experience verbally does not negate the possibility that an eligible if they were peer reviewed, accessible in either individual is experiencing pain and requires appropriate article or book (section) format and published between pain relief (cf. [18, 20, 21]). Because humans and verte- 2015 and March 2023. In the second screening step, a brates share similar neuroanatomical structures associ- more detailed analysis was performed, and papers were ated with pain processing, painful events in humans are assessed for the fit of

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ructures associ- more detailed analysis was performed, and papers were ated with pain processing, painful events in humans are assessed for the fit of addressing the principles of pain in also very likely to occur in vertebrates [22]. In fact, the pigs and pain in spontaneously occurring diseases and principle of analogy is often used to justify the use of injuries. Papers were considered eligible after this step if animals, including pigs, in the study of human pain or to they addressed one of the respective topics and presented argue for considering pain in painful conditions [1, 5, 11, results or reviews of clinical studies. Accordingly, papers 12]. To date, numerous studies have proven this assump- were excluded if they focused too much on pain manage- tion and outlined a great set of shared physiological pain ment procedures (e.g., docking, castration, ear notch- mechanisms, especially for pigs [23, 24]. ing) or if “pain” or related concepts were only addressed Moving from the definition of pain to the topic of ‘pain as a buzzword. Moreover, papers were excluded if they mechanisms’, however, requires defining the term noci- elaborated mainly on the discourse, ethics or attitudes ception. Nociception describes the reception of stimuli of people concerning the pain of pigs. In cases where no by nerve cell endings, called nociceptors. It comprises a publication was found, papers were retrieved following process by which the body encodes potentially or actually a snowballing technique. As outlined before, commonly damaging stimuli and initiates a series of events required used papers, standard books and literature published to transmit that information to the brain [25, 26]. Hence, before 2015 were also integrated. By help of this itera- the activation of

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rature published to transmit that information to the brain [25, 26]. Hence, before 2015 were also integrated. By help of this itera- the activation of nociceptors themselves does not neces- tive screening process, 49 publications were collected for sarily result in pain [25, 27]. In contrast, pain perception the search and review process. Additional metrics of the arises through cortical processing and comprises emo- search can be seen in supplementary materials (Addi- tional and perceptual (conscious) experiences [25]. In tional file 1). For reporting, the most suitable paper was other words, nociception may not always lead to pain and selected as the lead reference if several papers addressed other types of pain may occur without nociception (see the same aspect. To illustrate particular sections, addi- an overview in Table 1). tional material is provided as pictures and video footage. Types of pain are characterized by the different mech- The material is based on a study elaborating on timely anisms causing it (Table 1), but in clinical pain, they euthanasia of pigs suffering from pain and distress on overlap and evolve over time. To facilitate reading, the German farms [17]. following paragraphs are structured according to Table 1, as is common in the standard literature. Definitions and (patho‑)physiology of pain Research on pain has been conducted for centuries, and Nociceptive pain the definition of pain has evolved over time. In the fol- Processes of nociception lowing, the most relevant definitions and perspectives on Nociceptive pain is caused by the physiological activa- pain and pain mechanisms are presented together with a tion of peripheral high-threshold nociceptors. It plays narrative report of findings from the review. an important role in the

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esented together with a tion of peripheral high-threshold nociceptors. It plays narrative report of findings from the review. an important role in the protection of the body from fur- ther injury by initiating reflex and avoidance responses Pain and nociception [25]. Nociceptive pain can be induced by polymodal, The International Association for the Study of Pain peripheral sensory neurons (nociceptors) responding (IASP) is often cited both in human and veterinary medi- to noxious thermal, mechanical, or chemical stimuli. cine as the first reference to provide a definition of pain. Nociceptors encode the quality and quantity (e.g., dura- Its latest and adapted version outlines that pain is “[a]n tion, intensity, location) of noxious stimuli and transduce unpleasant sensory and emotional experience associated them into depolarizing action potentials (transduction). Kschonek et al. Porcine Health Management (2025) 11:12 Page 4 of 18 Table 1 Types of pain, including the description and biological function [28] Pain type Nociceptive pain Inflammatory pain Neuropathic pain Description Pain caused by physiological Spontaneous and stimu‑ Spontaneous pain caused activation of peripheral high lus- dependent pain evoked by lesions or disease of the soma‑ threshold nociceptors (subcatego- by both low-and high-intensity tosensory nervous system ries include somatic and visceral stimuli pain) Biological function Adaptive Protection of the organism Protection by hypersensitivity – (physi‑ from injury during healing and repair ological) Maladap‑ Persistent pain despite healing and absence of initial causes or trig‑ No protective function; may tive (patho- gers, may become a disease entity** on its own become a disease entity** on its physiolog‑ own ical) References

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protective function; may tive (patho- gers, may become a disease entity** on its own become a disease entity** on its physiolog‑ own ical) References from the review* Pig as a model Pig as model Pig as a model [24, 29] [37–40] [43, 44] Pigs in the focus of the publica‑ Pigs in the focus of the publica‑ Pigs in the focus of the publication tion tion [30, 31, 45, 46] [30–36] [41, 42] *Overview, some studies address several aspects; ** see [47] Nociceptive impulses are then transmitted to the spi- The initial pain, for example, is mediated by activation of nal cord by specialized afferent nociceptor fibres and thinly myelinated, fast-conducting Aδ fibres and can be Aδ- and C-fibres (transmission), [24, 27, 48]. The affer- perceived as brief, pricking and well-localized sensations ent nerve fibres enter the dorsal horn of the spinal cord. eliciting protective responses (e.g., immediate motor At that point, signal inhibition or amplification (modu- withdrawal response). The subsequent pain is mediated lation) occurs before the information is conveyed to the by unmyelinated, slow-conducting C-fibres that account brainstem, thalamus, limbic system and cortex (projec- for long-lasting, burning and less well-localized pain [51, tion). Finally, complex processing of sensory nociceptive 52]. The second pain seems to initiate (long-term) behav- signals can result in the perception of pain [26]. These ioural responses to limit further injury [52]. processes are illustrated in Fig. 1. Importantly, the transmission of nociceptive pain must Anatomical location of nociceptive pain not be understood as rigid. It is subject to plasticity since The anatomical location of tissue damage is associated modulation is a complex molecular process occurring with several typical

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ct to plasticity since The anatomical location of tissue damage is associated modulation is a complex molecular process occurring with several typical characteristics, such as the experi- at different levels of the central nervous system [49, 50]. ence and expression of nociceptive pain. In this respect, Moreover, individual experience and factors, such as the nociceptive pain can be differentiated into superficial and type of initial fibre conduction, influence pain sensation. deep somatic pain (skin, subcutis, muscles, joints, bones) Fig. 1 Schematic diagram of physiological nociceptive pathways by E. grosse Beilage (oriented on [3, 21]) Kschonek et al. Porcine Health Management (2025) 11:12 Page 5 of 18 and visceral pain (organs of the thoracic, abdominal, or that has no protective effect and should not be regarded pelvic cavities). Superficial somatic pain is initiated by as a continuation of acute pain [60]. the activation of nociceptors in the skin and mucous membranes, which are highly innervated. Therefore, this Inflammatory pain type of pain is well localized. Deep somatic pain origi- Inflammation is a physiological response of the body to nates from bones, muscles, joints, and connective tissues noxious stimuli, including (surgical) trauma or infection and is less well localized. Visceral pain originates from [56, 61], that is intended to evoke protective behaviour distension of hollow organs, mesenteric traction, ischae- to encourage healing. Inflammatory pain often accom- mia, and endogenous inflammatory mediators [26]. It panies diseases and injuries and is accompanied by a set possesses exclusive characteristics concerning perception of well-defined pathophysiological characteristics. There- and perceived anatomical location: the liver, lung and fore, it

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stics concerning perception of well-defined pathophysiological characteristics. There- and perceived anatomical location: the liver, lung and fore, it is important to understand more about its nature. kidney parenchyma, for example, are insensitive to pain, A variety of proinflammatory agents and mediators (e.g., while the capsule of the liver and kidney and the parietal ­ +, prostaglandins, bradykinin, cytokines, nerve growth H pleura possess nociceptors [53]. Visceral injury does not factor) are liberated following insult (see also paragraph necessarily result in visceral pain (e.g., cutting the intes- biomarkers) and sensitize nociceptive fibres directly or tine), while distention or traction may cause pain without indirectly [62, 63]. injuring the tissues [54]. Pain due to infections of the vis- Stimulation of nociceptors also leads to reverse (anti- cera, such as gastrointestinal disease, is commonly judged dromic) activation of C-fibres and subsequent release of to be very painful for pigs [12, 55]. Hence, diagnosing the neuropeptides, notably substance P (SP) and calcitonin source of visceral pain might be challenging because the gene-related peptide (CGRP). These peptides induce underlying pathology and the intensity of pain perceived vasodilation, plasma extravasation, oedema, and fur- by the individual animal are not necessarily closely cor- ther sensitization of nociceptors and thus contribute to related [26]. Moreover, visceral pain is diffuse and poorly neurogenic inflammation [64, 65]. It is well known that localized due to the sparse innervation of visceral organs complex bidirectional neuroimmune interactions modu- and the spread of visceral afferents across several lami- late inflammation and pain [66]. In this context, nerve nae as well as segments

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ctions modu- and the spread of visceral afferents across several lami- late inflammation and pain [66]. In this context, nerve nae as well as segments when terminating in the spinal growth factor (NGF) was found to be an important sig- cord, thereby inducing large receptive fields [49, 54]. nalling molecule involved in mediating postoperative and Due to convergence of visceral and somatic nociceptive osteoarthritic (OA) pain. Briefly, its interaction with the input in the spinal cord, visceral pain is often charac- tropomyosin receptor kinase A receptor (TrkA) has been terized as referred pain, meaning that pain is perceived demonstrated to induce alterations in primary afferent adjacent to or at a distance from the noxious stimulus, nerve fibres and immune cells, sustaining and enhancing typically at somatic sites (e.g., angina pectoris in humans pronociceptive states [67]. Recently, anti-NGF monoclo- leading to pain in the arm) [49, 54]. Finally, visceral pain nal antibodies have been approved for the treatment of can be accompanied by emotional (affective) and auto- osteoarthritic pain in dogs [68] and cats [69]. nomic responses such as nausea, vomiting, sweating and Most of the literature included in this review assessed changes in blood pressure and heart rate because of auto- inflammatory pain in pigs, with translational interest in nomic innervation of the visceral organs [53, 54]. inflammatory skin diseases in general [38]. Practition- ers can refer to these and other findings about cutaneous hyperalgesia (i.e., abnormally increased sensitivity to pain Duration of nociceptive pain in response to a normally painful stimulus) due to UV-B The sensation of pain can be further differentiated into irradiation [37, 40] when examining an individual pig acute and

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painful stimulus) due to UV-B The sensation of pain can be further differentiated into irradiation [37, 40] when examining an individual pig acute and chronic pain, depending on how long the sen- with impaired skin conditions or sunburn and the need sation lasts. Acute pain (or adaptive pain) has a protec- to judge upon the pain state. While the depth of findings tive function and is essential to the organism because it cannot be resumed at this location, behaviour appears enables healing and tissue repair and thus the animal’s to be a valid parameter for observing inflammatory pain wellbeing [56]. Chronic pain was arbitrarily defined as and hyperalgesia following irradiation, at least in familiar pain persisting or recurring for more than 3 months [57]. or controlled environments [37]. In addition to the time span, initiated alterations in pain pathways and induced changes in the nervous system Neuropathic pain are of particular concern. The latter may contribute to Neuropathic pain is initiated by lesions of the somatosen- physiologic, metabolic, and immunologic alterations [25] sory system [20, 28]. This pain may result from periph- and affect the quality of life of animals [58, 59]. Hence, eral or central nerve injury following acute events (e.g., chronic pain refers to maladaptive or pathological pain amputation, spinal cord injury, freezing) or systemic or Kschonek et al. Porcine Health Management (2025) 11:12 Page 6 of 18 local diseases (e.g., viral infection, neoplasia) [26, 61]. repeated C-fibre stimulation or ‘wind-up’. It describes Following such damage, a cascade of neurochemical and an increased pain sensation that is caused by repeated neuroplastic changes and altered expression of ion chan- noxious stimuli [26]. Some of the mechanisms of ‘wind-

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n sensation that is caused by repeated neuroplastic changes and altered expression of ion chan- noxious stimuli [26]. Some of the mechanisms of ‘wind- nels can lead to spontaneous painful sensations without up’ are thought to be related to altered pain states [76]. an associated stimulus. Unlike inflammatory pain, which Molecular factors that contribute to central sensitiza- often subsides after the stimulus is eliminated, neuro- tion include N-methyl-D-aspartate receptor (NMDA)- pathic pain can persist or become chronic [22]. Neuro- mediated signalling, disinhibition, and microglial pathic pain can therefore be regarded as a maladaptive activation, among others [56, 62]. Overall, peripheral phenomenon leading to severe and long-term conse- and central sensitization may contribute to altered pain quences for quality of life in humans [70] and animals [3]. states such as hyperalgesia (i.e., an exaggerated and prolonged response to noxious stimuli) and allodynia, a condition in which pain is caused by an innocuous Sensitization and altered pain states stimulus (e.g., touching the skin) [22, 71]. In addition to the protective function of nociceptive pain, high-intensity and/or prolonged noxious stimuli can result in sensitization [26]. Sensitization of the noci- Clinical pain ceptive system can be longer lasting but is reversible and The above-mentioned categorization of pain types pro- evokes protective processes to avoid further injury [71]. vides a good overview and understanding of the com- As described above, tissue injury and inflammation lib- plex topic of “pain”. Nonetheless, the clinical pain that erate a variety of mediators (‘sensitizing soup’) [64], cre- practitioners encounter on a daily basis is usually a mix- ating an altered molecular

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hat erate a variety of mediators (‘sensitizing soup’) [64], cre- practitioners encounter on a daily basis is usually a mix- ating an altered molecular environment that leads to a ture of different pain types. This can be illustrated using reduction in the activation threshold and an increase in the example of tail biting [77]. Following the initial the responsiveness of peripheral nociceptors [26, 64, 72]. insult, acute superficial somatic pain may be suspected. This so-called peripheral sensitization is closely linked to Over the course of time, due to the necrotizing puru- the site of tissue damage [73]. lent character of those lesions, inflammatory pain and Intense, prolonged or repeated nociceptor input can possibly neurogenic inflammatory processes emerge. trigger the excitability and pain transmission of neurons Depending on the degree of neural injury, neuropathic in central nociceptive pathways (i.e., the spinal cord and pain is likely to develop. Indeed, in an experimental supraspinal structures) [22, 74]. Additionally, a reduc- study of pigs that underwent tail amputations, sensiti- tion in inhibitory pathways and the recruitment of sub- zation and sustained alterations in peripheral sensitiv- threshold synaptic inputs may lead to increased action ity resembling neuropathic pain were observed [31]. In potential output [71]. These processes of pain facilitation fact, the transition from physiological to pathological and pain disinhibition may contribute to a state called pain conditions often occurs frequently. Pathological or central sensitization. Consequently, central sensitization maladaptive pain has no protective function [64]. This to nociceptive and innocuous stimuli is characterized pain state is mostly persistent or recurring, even long by

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has no protective function [64]. This to nociceptive and innocuous stimuli is characterized pain state is mostly persistent or recurring, even long by diffuse pain sensitivity and pain hypersensitivity. In after the traumatic event or illness subsides or if acute contrast to peripheral sensitization, central sensitization pain is inappropriately managed or untreated. is subject to changes in the properties of neurons in the This latter factor is especially important for practi- central nervous system, meaning that painful sensations tioners. Even if the initial cause is absent, pain due to occur even after a stimulus is withdrawn [71]. Moreo- traumatic lesions may (re)occur over time. Initial ideas ver, inputs to dorsal horn neurons from the activation of on how to assess and validate pain in amputated body low-threshold Aβ fibres, which normally convey innocu- parts in this regard may be inferred by studies elabo- ous tactile stimuli, may contribute to central sensitization rating on tail amputations [30, 31, 45, 46, see chapter [75]. All these phenomena emphasize the plasticity of the nociception]. Another example is for practitioners who somatosensory nervous system in response to activity, face chronically lame animals. Indicators such as the inflammation, and neural injury [71]. It should be noted walking pattern (among others), as well as hints for here that neuropathic pain and central sensitization are diagnostic anaesthesia and evaluation protocols, may not synonymous since the latter is initiated by intense or be derived from studies on neuropathic pain models prolonged nociceptive inputs, irrespective of the origin [43, 44]. of pain (nociceptive, inflammatory, or even neuropathic) [72]. Pain as a disease entity Sharing some characteristics of central

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f the origin [43, 44]. of pain (nociceptive, inflammatory, or even neuropathic) [72]. Pain as a disease entity Sharing some characteristics of central sensitiza- Although one incident can activate several pain types, tion is the temporal summation of pain caused by the sensation of pain may also appear or be sustained Kschonek et al. Porcine Health Management (2025) 11:12 Page 7 of 18 irrespective of the trigger, cause or healing process. Pain gastrointestinal diseases and injuries [3, 82, 83] or urinary may be a self-standing disease entity in this respect, and [84] and respiratory tract diseases [39]. Veterinarians pigs should be examined and treated for this diagnosis, who report field cases with the help of the above-defined similar to any other common swine disease. terms will enhance the practice-research dialogue and Pain as a disease entity in pigs includes both acute and refine the understanding of pain in pigs. chronic pain. Although it is difficult to diagnose pain in pigs (and treat different pain types with respect to avail- Pain assessment in pigs able medication), the consequences in terms of welfare Assessing pain in pigs requires knowing well about the and costs of neglected cases are high [58, 59]. If no pain typical behaviour of the species as well as the potential alleviation is possible, pigs may even have to be eutha- idiosyncrasies of the individual since pigs often tend to nized with respect to the definition of mercy killing [15]. hide their pain [2, 85, 86]. The indicators relevant for pigs In human medicine, discussions on how to diagnose range from physiological to behavioural aspects, and the and define pain as a disease entity are currently underway latter is mostly used by practitioners [87]. Currently, no [47, 78]. Future studies on pain

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and define pain as a disease entity are currently underway latter is mostly used by practitioners [87]. Currently, no [47, 78]. Future studies on pain in pigs should elaborate harmonized nomenclature or categorization of indicators on this topic as well, but in the first step, awareness of has been established [3, 12]. While it is out of scope for the need to document the diagnosis of pain as well as the this article to suggest a harmonized system, orienting to appropriate treatment needs to be improved. other fields shows that methods of pain assessment can differ according to the focus on spontaneous or evoked Implications and outlook behaviour but also in terms of how the pain is scaled. What further implications do the terms and definitions Using a “subjective verbal pain scale”, for example, of pain and pain mechanisms have for everyday practice? a practitioner describes the pain state with qualify- One answer is that practitioners can apply the updated ing words such as “moderate” or “severe” pain. Using a knowledge and re-evaluate individual cases. For example, “categorical scoring systems”, these words were associ- when examining a pig with accidently amputated body ated with numbers (mild, 1; moderate, 2; severe, 3), and parts such as a dew claw, a veterinarian should deter- a set of indicators was predefined for assessment (such mine whether common signs of chronic pain appear, as as motion (movement behaviour, such as the movement described in recent republications [30, 31, 45, 46, 79]. to the feeder) or body condition (that can be affected Another answer is that the updated knowledge leads to by pain sensitivity). Once the scores are noted, they are a change in perspective: rather than assuming that pain weighted according to relevance for

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by pain sensitivity). Once the scores are noted, they are a change in perspective: rather than assuming that pain weighted according to relevance for the species or dis- is not present in a pig, veterinarians should ask if enough ease to calculate the sum and thus overall pain score of evidence is present to reject the assumption that an indi- the assessment. Several further pain scales exist (visual vidual pig is experiencing pain. According to recent pub- analogue, numerical rating, simple descriptive or grimace lications, individuals were asked whether a nonresponse scales), and they were developed to improve the reliabil- to stimuli may be explained by the fact that the pig is ity, validity and objectivity of measuring pain in animals distracted by examinations (cf. role of consciousness, [21]. [35]) or because it remembers previous routine visits and Concerning pain in pigs, similar efforts and discussions avoids being (painfully) re-examined (cf. role of habitua- are underway [3, 12, 88]. For example, a recent study tion, [34, 36, 80]). Moreover, if a pig scores lower on pain evaluated the value of behavioural pain scales for pigs. It scales than expected, practitioners should consider how was concluded that the overall evidence for the UPAPS this state was experienced by humans or whether the (Unesp-Botucatu Pig Composite Acute Pain Scale) is pig may simply belong to a type less expressive of pain, strong and that the overall evidence for the PGS-B (Pig- just as there are different personalities and coping styles let Grimace Scale-B) is moderate for assessing pain in among humans [59, 81]. cases of castration and tail docking, respectively [88]. In sum, incorporating the latest knowledge about terms The use of these scales among practitioners who assess and

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and tail docking, respectively [88]. In sum, incorporating the latest knowledge about terms The use of these scales among practitioners who assess and definitions of pain means that practitioners should pain induced by spontaneously occurring diseases and focus on individual pigs and reconsider whether remote injuries has yet to be assessed. However, these scales rely observation is needed or at least if additional time is on indicators such as attention given to the affected area, needed to re-evaluate the first impression about individ- interactive behaviour, ear position, and orbital tightening ual pain states. (spontaneous behaviour), which are also major concerns Furthermore, learning about the state of related for stable veterinarians. Hence, knowing about recent research underlines how invaluable the perspective of developments in pain scales and indicators is essential for pig veterinarians is for improving knowledge in the field. ensuring the best evaluations of pain in pigs. For example, few studies have examined pain due to Kschonek et al. Porcine Health Management (2025) 11:12 Page 8 of 18 For pigs unfamiliar with typical pain behaviour, how- or noises from technical equipment. Unaffected pigs ever, the first step is to know and understand indicators direct their attention towards any action. In affected pigs, before they can be detected in a pig. In this regard, the reduced attention can range from listlessness (mild) to most common indicators of pain in pigs will be discussed lethargic (severe) states [87]. However, restlessness can and described with additional materials. also indicate pain [96]. How pigs engage with their pen mates is called ‘social interaction’. Affected pigs exhibit Behavioural parameters self-separation [6, 87] by lying close to

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igs engage with their pen mates is called ‘social interaction’. Affected pigs exhibit Behavioural parameters self-separation [6, 87] by lying close to the wall or in The term “behaviour” summarizes the overall senso- corners and by reducing their encounters with other motoric expression of an animal [89] and is classified as pigs. Indeed, social isolation may even be a more spe- abnormal when it differs in pattern, frequency or context cific indicator of pain than general interaction behaviour from the behaviour shown by most members of the spe- [82]. Defence in dominance-related interactions with pen cies [90]. Behavioural changes associated with pain have mates is reduced among pigs experiencing pain. mainly been deduced from spontaneously occurring Reduced feed intake is one of the most frequently used behaviours arising or increasing in the context of pain- overall indicators for disease but cannot be considered ful conditions induced by damaging management proce- valid pain indicators, as specificity is likely low and dif- dures [12]. Pain assessment based on behaviour analysis ficult to evaluate in pigs fed ad libitum and housed in has the advantage that it is not invasive, does not require groups [87]. equipment or restraint, and can be assessed by remote Interpretation of vocalization as a pain response observation [4]. Nonetheless, the evaluation of behaviour requires consideration, as some painful events induce during a clinical examination might be confounded by vocalization, while other pain-related events suppress pig-examiner interactions [12, 91]. vocalization [3]. There is clear evidence that vocalization Behaviour, evaluated in terms of pain, consists of the is indicative of pain [3]. For example, technical analysis expression of various

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t vocalization Behaviour, evaluated in terms of pain, consists of the is indicative of pain [3]. For example, technical analysis expression of various indicators, describing how a pig is of individual vocalizations recorded from piglets showed reacting to its environment, interacting with pen mates, that calls differed between various conditions (pain, cold and showing vocalization, muscle activities and changes and hunger) and could be detected with an accuracy rate in posture or locomotion. A set of clinical parameters, of 81% [97]. In another study using multiparametric call such as the amount of time spent time walking, rest- analysis to classify vocalizations during castration pain, ing, sleeping, rooting, and interacting, as well as longer three call types were distinguishable (grunt, squeal, durations spent in an abnormal posture, walking with scream). In comparison, screams appeared to be pain difficulty, and lying alone, have recently been validated related, as the piglets that were castrated without local to indicate pain after surgery [4]. Even though this fully anaesthesia produced almost twice as many screams as validated scale for acute pain is based on longitudinal piglets that were castrated with anaesthesia. The screams video analysis [4], it shows the general suitability of the during castration also became more extended and more parameters. To assess clinical signs of spontaneously powerful [98]. The total call energy, sound pressure level, occurring diseases and injuries, individuals of the same peak-to peak pressure, maximum call frequency and group or pen of unaffected pigs should serve as a refer- temporal characteristics of the individual call can also be ence during an on-farm examination of individuals [81, used as indicators of pain [99].

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r- temporal characteristics of the individual call can also be ence during an on-farm examination of individuals [81, used as indicators of pain [99]. However, not every call 82]. A comparison of this level and an evaluation of a set represents pain; for example, inadequate handling may of indicators will help to identify substantial differences also provoke vocalization [100]. Hence, vocalizations from normal behaviour [4], but subtle changes may be must be examined in a particular context. For example, overlooked. if a lame pig is screaming while walking without being Several pain scales have been developed for various moved forward, it is likely that the vocalization is an indi- species and different purposes [4, 92–95], and as out- cator of pain (Additional file 2). lined in [88], pain scores in pigs are already under way. Teeth grinding (bruxism) is also indicative of pain [87]. Future research could explore whether these are help- Identification of this characteristic noise under on-farm ful tools for decision making about pain management conditions requires an experienced examiner, as teeth in spontaneously occurring diseases or injuries or about grinding is often drowned out by other environmental pain treatment for veterinary practitioners. Moreover, noise (Additional file 3). it is important to consider and evaluate the behavioural Tremor or trembling is a subtle indicator of pain. While changes known to be indicative of pain in pigs. shivering might be caused by low temperatures, tremors The parameter ‘attention’ summarizes how a pig are limited to the skeletal muscles (Additional file 4) of a responds to the environment, e.g., caretaker, examiner Kschonek et al. Porcine Health Management (2025) 11:12 Page 9 of 18 part of the body and are considered to

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the environment, e.g., caretaker, examiner Kschonek et al. Porcine Health Management (2025) 11:12 Page 9 of 18 part of the body and are considered to indicate pain [12, (OA) of the distal tarsal joints is a frequently diagnosed 87, 101]. disorder causing lameness and is referred to as “bone Tail posture can be used to indicate pain. Tail posture spavin”. In general, medical and surgical treatments aim and motion are impaired in docked tails [102]. When to accelerate fusion of the affected tarsal bones to provide tails are undocked or when only the tip is docked, a pain relief [108]. However, even in horses undergoing curled tail as well as a relaxed hanging or loosely wag- surgical arthrodesis, the resolution of lameness took up ging tail are associated with positive valence (emotional to 12 months [108]. To the authors’ knowledge, there is states) and high or low arousal, respectively. A constantly no comparative literature on pigs. However, anatomical tucked, motionless tail indicates negative valence and confirmation of the corresponding joints differs between low arousal, while a tail tucked in a sudden response horses and pigs. to a threat is associated with negative valence and high Grimace scales have been used to evaluate behavioural arousal [102]. Tucked tails can be observed in cases of changes and the facial expressions of piglets, growers and pain, sickness and fear. Tail tucking due to tail biting is sows induced by tissue damage or disease [109–113]. often chronic and results in an almost permanently or Facial expressions comprise a number of anatomically frequently tucked tail [102, 103]. Tail wagging includes based actions, such as changes in the shape of the eyes, the side-to-side movement of the tail. Relaxed wagging nose, cheeks, mouth and

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gging includes based actions, such as changes in the shape of the eyes, the side-to-side movement of the tail. Relaxed wagging nose, cheeks, mouth and ears [114]. In piglets, orbital (tail swinging) occurs during various social behaviours, tightening might be an indicator of pain induced by cas- locomotor and social play and locomotion. However, tration [109, 115]. This phenomenon is evaluated in the intense tail wagging in pigs with biting lesions can be a PGS-B grimace scale (among ear position, cheek tighten- sign of distress, tail irritation, or pain and can occur in ing, nose bulge), which has been shown to have a strong pigs that are victims of tail biting [102]. level of evidence [88]. However, the use of grimace scales Body posture also provides valuable information about for pain evaluation is not yet ready for use in practice, as pain in pigs [3]. Kneeling is a strong indicator of pain it requires extensive video recording. Currently, research and is aimed at relieving painful parts of the body, e.g., focusing on automated pain recognition based on deep lower parts of the forelegs, hind legs or abdomen (Addi- learning models is of particular interest in numerous tional file 5 and Additional file 6). Tripping, i.e., the rapid mammalian species [116–118]. Interestingly, a real-time change between burdening and not burdening a foot or facial recognition platform has been proposed for pigs leg, is also a response to pain and is indicative of pain and cows aiming to detect emotions [119]. In the future, in more than one foot or leg (Additional file 7). Stand- we will show whether these systems have the potential to ing motionless with the head down might be caused by become reliable and valid tools in daily veterinary prac- pain but also indicates suffering

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al to ing motionless with the head down might be caused by become reliable and valid tools in daily veterinary prac- pain but also indicates suffering [12]. Postural change tice for detecting painful conditions. while sitting is indicative of pain, e.g., when a pig is try- ing to unburden a hind leg by bending the spine to place Physiological parameters (biomarkers) the leg in an upper position (Additional file 8), pain may In addition to behaviour, physiological parameters be reduced under pain treatment [42]. An arched spine (Table 2) can indicate painful conditions in animals. Pain- while the pig is standing or moving is also a sign of pain ful stimuli lead to activation of the sympathetic nervous located in the locomotor system or inner organs. Hud- system and release of catecholamines, resulting in physi- dling, i.e., lying with at least three legs under the body or cal reactions. These include changes in cardiopulmonary lying in a stiff position, is another sign of pain ([12], p.4). parameters, as well as changes in skin temperature, pale Lameness is a reduction in weight borne and expressed mucous membranes, mydriasis, salivation, and decreased by carrying a foot, favouring a leg, or being unable to get activity in the gastrointestinal and urinary systems [3, up and move and it is an important indicator of pain in 120]. As nociceptive indicators, cardiovascular param- terms of severity [12]. Lame pigs exhibit asymmetrical eters are often inconsistent and not pain specific, as weight bearing between legs, increased step frequency they are influenced by many factors in addition to pain, or stand time, tip-toe walking and altered stride length such as stress; homeostatic mechanisms [121]; medi- [104–106]. A previous study stated that locomotor dis- cations; and

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king and altered stride length such as stress; homeostatic mechanisms [121]; medi- [104–106]. A previous study stated that locomotor dis- cations; and the intensity, type, and location of noxious orders do not necessarily result in pain [3], as individu- stimuli [122]. Elevated catecholamine concentrations, as als may be affected by a biomechanical abnormality [12]. well as glucose and lactate concentrations resulting from In another publication, it was suggested that “[…] joint catecholamine-stimulated glycogen mobilization [123], injuries may prevent normal movement of the joint, lead- have been detected in porcine blood as indicators of pain, ing to stiffness in gait”, ([107], p.66) which may not be although mostly in association with damaging manage- associated with pain. However, this statement may need ment procedures such as piglet castration and tail dock- to be interpreted with caution. In horses, osteoarthritis ing [3, 124]. Kschonek et al. Porcine Health Management (2025) 11:12 Page 10 of 18 Table 2 Physiological parameters and biomarkers Category Physiological parameter/biomarker References Activity of the autonomous nervous system Heart rate/heart rate variability [127, 133–137] Arterial blood pressure Respiratory rate Temperature (rectal, skin, eye) Hormonal concentrations in blood, saliva or urine Adrenal axis: ACTH, cortisol [138, 139] Sympathetic axis: adrenaline, noradrenaline, chromogranin a [140–142] Neuropeptides (substance p, beta-endorphin) [143, 144] Blood energetic metabolites Glucose [82, 133, 139] Free fatty acids Lactate Blood concentrations of inflammatory ­markers* Cytokines (interleukin-1, tumour necrosis factor-alpha) [42, 77, 143, 145, 146] Acute phase proteins (serum amyloid a, c-reactive protein, haptoglobin, fibrinogen)

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terleukin-1, tumour necrosis factor-alpha) [42, 77, 143, 145, 146] Acute phase proteins (serum amyloid a, c-reactive protein, haptoglobin, fibrinogen) Enzymes Creatine kinase [127, 146, 147, 148] Salivary α-amylase Total esterase activity and its components (lipase, cholinesterase etc.) Pterines Neopterine [149, 150] Biopterine Proto-Oncogenes c-Fos [151, 152] Physiological parameters and biomarkers that have been used for pain identification in pigs (adapted from [124] with exemplary studies for each category). * Inflammatory markers indicate the existence of an inflammatory state that may generate pain Cortisol is the most commonly used blood parameter levels [132]. Moreover, the delay in diagnosis does not for assessing pain in pigs in experimental settings. Corti- allow for rapid on-farm decisions, which are essential in sol is a steroid hormone produced by the adrenal gland in cases of severe, spontaneous disease in individual pigs. response to stress, and it can also increase in response to pain [125]. Studies have widely examined cortisol/adren- Other approaches to measure pain ocorticotropic hormone (ACTH) levels in blood plasma, Although several indicators have been mentioned and serum and saliva in pigs in relation to pain [12]. Damag- even more may be discussed in other reviews [3, 12], ing management procedures aside, painful events such as forthcoming and digitally assessed approaches need intramuscular injections [126], lameness [127, 128], and more attention. Electroencephalography (EEG), for rectal prolapse [127] were found to result in significantly example, provides a summation of electrical activity aris- elevated cortisol levels in blood or saliva. A more recent ing from the cerebral cortex. Currently, the application method of cortisol

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activity aris- elevated cortisol levels in blood or saliva. A more recent ing from the cerebral cortex. Currently, the application method of cortisol determination in pigs involves detec- of these methods is limited by the experimental setting tion in bristles. Findings showed that, compared with [153–155]. those in control groups, pigs suffering from chronic pain Infrared thermography (IRT) is a technique used to from tail biting or lameness during their lifetime had ele- evaluate inflammatory conditions in pigs [156]. It is com- vated cortisol levels in bristles [129], while avoiding any monly used in laboratory settings, but recent studies have invasive, painful procedures in piglets resulted in lower used this technique under field conditions and found it to cortisol levels at weaning age [130]. Thus, cortisol levels be very effective for the early identification and treatment in bristles could be a suitable indicator of animal welfare. of shoulder ulcers in sows [157]. Additional biomarkers (included metabolic, immuno- Another digital device for assessing pain sensitivity in logical, and inflammatory markers) have been identified pig skin and underlying tissues (e.g., osteoarthritis, syn- as indicators of pain in pigs [124]. Most of these biomark- ovitis) is the hand-held pressure application measure- ers, however, were examined in experimental settings and ment (PAM) device. This device enables the application have not been validated for pain assessment in individual of force and the monitoring/measurement of mechani- pigs with naturally occurring diseases [3]. Overall, the cal nociceptive thresholds. The approach is promising determination of laboratory parameters has limited rel- because of the need to constrain pigs during measure- evance for routine

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approach is promising determination of laboratory parameters has limited rel- because of the need to constrain pigs during measure- evance for routine clinical pain assessment. These param- ment, apply consistent stimuli (exertion of force per area) eters do not always allow for a clear inference of pain, as and gather objective and consistent evoked responses. some markers respond to both pain and stress [131] and [32, 34, 35, 158, 159]. show natural circadian variations in their concentration Kschonek et al. Porcine Health Management (2025) 11:12 Page 11 of 18 In the future, practitioners may use and evaluate the Among the list of drugs for pigs, NSAIDs are com- role of cognitive tests (such as memory tests or spatial monly used in porcine health management and should be memory tasks) in the field. Especially for critics and as a selected given the indication, location, nociceptive path- complement to nociceptive measures, this approach will way and agent of concern [161]. Most commonly, meloxi- enhance the understanding of the affective-motivational cam and ketoprofen are used as anti-inflammatory and dimension of pain (cf. [3, 12, 58, 160]). analgesic drugs for farm animals [87, 163]. NSAIDs act More commonly used in current practice is analgesic at the periphery by targeting specific molecules involved treatment (diagnostic anaesthesia), which is a tool for in nociception in sensory neurons [2], and some have identifying pain in an individual pig. The ability of anal- central analgesic effects [161]. NSAIDs have been found gesic drugs (or anaesthetic techniques) to alleviate the to be effective at alleviating inflammation but not neu- effects of tissue damage is indicative of the presence of ropathic pain [164]. Depending on the injury of concern, pain [3, 114].

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mmation but not neu- effects of tissue damage is indicative of the presence of ropathic pain [164]. Depending on the injury of concern, pain [3, 114]. The response to an analgesic treatment experiences and recommendations for using NSAIDs for allows, to a certain degree, us to conclude that pain, but pigs in cases of mastitis [87, 165], lameness [166], inci- not every medicine, is potent for all kinds of pain [161]. sional insult [41] or shoulder ulcer [42] have also been Hence, the absence of pain reduction after treatment may published. indicate that the chosen pathway for relief failed instead Irrespective of the disease or injury, the half-life of a few of assuming that pain was generally absent [162]. hours for NSAIDs in pigs [167] requires the provision of In summary, depending on the location and kind of more than one dose per day. Despite this limitation, the injury or disease, practitioners can use and should com- use of anti-inflammatory and analgesic agents is rated as bine a set of behavioural, physiological and digitally the most effective method for reducing pain among ani- assisted approaches to elicit the pain state of an individ- mals [87, 168], and many studies have proven its efficacy ual pig. for treating pain in pigs [105, 169, 170]. However, most NSAIDs are licenced to control pyrexia (Table 3), and few Pain therapy in pigs studies have examined the effective dose of NSAIDs for Veterinarians are responsible for providing the best pos- other indications [41, 161, 167]. Hence, further collabo- sible treatment. As outlined in the previous paragraphs, ration between researchers and practitioners concerning there is no doubt that pigs can sense pain. Hence, treat- common adverse effects on healing [42] or even long- ment will have to include pain

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ncerning there is no doubt that pigs can sense pain. Hence, treat- common adverse effects on healing [42] or even long- ment will have to include pain alleviation, regardless of term effects are needed [161, 171]. the challenges in clinical pain diagnosis. The list of avail- In addition to NSAIDs, opioids can be successfully able drugs for treating pain in pigs is short, and pain is used to relieve (inflammatory) pain in model studies [38]. not a delimited indication. In this context, the following However, opioids are not licenced for general use in pigs considerations will help generate a protocol for treating [161]. In this respect, additional research is needed to pain in pigs due to spontaneously occurring diseases and broaden the range of potential drugs available for pigs, injuries. Table 3 Licenced NSAIDs and related drugs in Germany Agent Dosage (mg/kg BW) Application (times Application route Maximum duration References a day) treatment (day) Acetaminophen 30 1 [24 h] P.O. (drinking water) 5 [172, 173] Acetylsalicylic acid 30 2 P.O. (feed) 3 [174, 175] 50 1 P.O. (feed) 5–10 Flunixin 2–2.2 1 IM 1–3 [176, 177] Ketoprofen 1.5–3.0/ 1 [24 h]/ P.O. (drinking water)/ 1/ [178–180] 3.0 1 IV, IM 1 (-3) Meloxicam 0.4 1 IM 1 (-2) [181–183] Metamizole 15–50 Once/ P.O./ 1/ [184] 3 [8 h] IM, IV As needed Sodium salicylate 35 1 P.O. (drinking water) 3–5 [185] Tolfenamic acid 2.0 Once IM 1 [186] An example of licenced NSAIDs and related drugs in Germany for application in pigs (modified from VETIDATA, https://​vetid​ata.​de). For more information, refer to the search database of the European Medicines Agency (EMA, https://​www.​ema.​europa.​eu/​en/​medic​ines); max. maximum; P.O. Oral; IM Intramuscular; IV Intravenous; p8h every 8 h Kschonek

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dicines Agency (EMA, https://​www.​ema.​europa.​eu/​en/​medic​ines); max. maximum; P.O. Oral; IM Intramuscular; IV Intravenous; p8h every 8 h Kschonek et al. Porcine Health Management (2025) 11:12 Page 12 of 18 (see another discussion and overview with indications in topics. The paper provides guidance for practitioners [192]). based on the findings, details and intricacies of the latest Importantly, the failure to treat acute (perioperative) research about pain in pigs. Limit of this article is that the pain may promote the emergence of peripheral and cen- search string included the term “not” and excluded the tral sensitization and maladaptive pain conditions [187]. term “patients”. Nevertheless, given the understanding of the mecha- More research about pain is necessary to increase nisms of the different pain types, it seems rational that knowledge about the diseases and injuries that veterinar- the administration of NSAIDs alone may be inadequate if ians observe when examining pigs. One way to increase maladaptive or chronic pain conditions can be assumed. this knowledge is to link assumptions in research back to In terms of a multimodal analgesic approach (i.e., the basic principles that drive every detrimental condition. use of 2 or more analgesics or techniques to target dif- Another way is to invite practitioners to provide more ferent nociceptive pathways) [188], it would therefore be informed and detailed reports about treatment proto- favourable to add adjunctive drugs to the therapy plan. cols for painful conditions in pigs. In this way, practice- Ketamine, an N-methyl-D-aspartate receptor (NMDA) research dialogue will help to obtain more evidence antagonist, is administered at subanaesthetic doses and about pain induced by

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tate receptor (NMDA) research dialogue will help to obtain more evidence antagonist, is administered at subanaesthetic doses and about pain induced by spontaneously occurring diseases is known to modulate central sensitization and exert and injuries in pigs. antihyperalgesic effects [187, 189]. However, ketamine is licenced for pigs for the purpose of injectable anaesthesia. Closely related to enhancing the knowledge about the Short list for practitioners use of drugs for pain alleviation, knowledge about pain intensity is needed to evaluate the effect of analgesics. • A pig that has been confirmed to be experiencing For practitioners, these data are relevant for attenuat- pain should receive adequate treatment ing the analgesic protocol. For example, a study found • Even a likely painful condition is enough reason to that the upper limit of mild pain scores and the diagnos- treat a pig for pain tic uncertainty zone overlap [190], indicating that pigs • The fact that drugs are scarce, and pain identification undergoing moderate pain should already receive analge- is not easy does not justify leaving a pig suffering in a sia [4]. However, even if no data for diagnostic zones are painful condition available in practice, the results of this study recommend • To identify pain among pigs, veterinarians and care- initiating pain therapy when pain is identified by behav- takers need deep knowledge about the basic princi- ioural changes and/or on the basis of a diagnostic evalu- ples of pain mechanisms; this article can be used as ation. In the latter case, it is not absolutely necessary to a starting point for narrowing knowledge gaps and prove pain in the individual before starting the therapy. identifying articles for further reading Pig veterinarians and farmers

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ng knowledge gaps and prove pain in the individual before starting the therapy. identifying articles for further reading Pig veterinarians and farmers need to consider incorpo- • Scales and scores for identifying pain in pigs exist but rating the judicious use of analgesics into standard oper- need further validation in clinical settings; moreover, ating procedures as a way of improving welfare [191]. In the current knowledge is sufficiently valid to prevent summary, monitoring the success of treatment is pivotal. unnecessary pain in pigs Every practitioner should be aware that untreated or persistent pain can negatively affect health, welfare and quality of life. Nevertheless, in situations in which suffer- Supplementary Information ing and pain cannot be addressed, euthanasia should be The online version contains supplementary material available at https://​doi.​ regarded as the only viable option [187]. org/​10.​1186/​s40813-​025-​00421-0. Additional file 1. Metrics of the review. The table provides an overview of Conclusion the search output and filter processes. Knowledge about the basic mechanisms, assessment and Additional file 2: Vocalization. The video shows a lame pig screaming while treatment of pain among pigs is needed to ensure that walking. Permission to reuse the materials for the purpose of illustrating the signs and arguments of the authors in this article is granted. detrimental conditions among these animals are detected Additional file 3: Teeth grinding. The video shows a pig teeth grinding and alleviated in everyday practice. This article summa- under environmental noise. Permission to reuse the materials for the rizes basic knowledge on this topic and invites readers to continue reading based on outlined references and Kschonek et

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o reuse the materials for the rizes basic knowledge on this topic and invites readers to continue reading based on outlined references and Kschonek et al. Porcine Health Management (2025) 11:12 Page 13 of 18 3. Herskin MS, Di Giminiani P. Ch. 11 - Pain in pigs: Characterisation, purpose of illustrating the signs and arguments of the authors in this mechanisms and indicators. In: Špinka M, editor. Advances in Pig Wel‑ article is granted. fare: Woodhead Publishing; 2018. p. 325–55. Additional file 4: Trembling. The video shows a pig with subtle trembling. 4. Luna SPL, de Araújo AL, da Nóbrega Neto PI, Brondani JT, de Oliveira FA, Permission to reuse the materials for the purpose of illustrating the signs Azerêdo LMDS, et al. Validation of the UNESP-Botucatu pig composite and arguments of the authors in this article is granted. acute pain scale (UPAPS). PLoS ONE. 2020;15(6):e0233552-e. https://​doi.​ org/​10.​1371/​journ​al.​pone.​02335​52. Additional file 5: Kneeling 1. The video shows a kneeling pig. Permission to 5. Marchant-Forde JN, Herskin MS. Ch. 16 - Pigs as laboratory animals. In: reuse the materials for the purpose of illustrating the signs and arguments Špinka M, editor. Advances in Pig Welfare: Woodhead Publishing; 2018. of the authors in this article is granted. p. 445–75. Additional file 6: Kneeling 2. The video shows a kneeling pig. Permission to 6. Prunier A, Tallet C, Sandercock DA. Evidence of pain in piglets subjected reuse the materials for the purpose of illustrating the signs and arguments to invasisve management procedures. In: Edwards S, editor. Under‑ of the authors in this article is granted. standing the behaviour and improving the welfare of pigs. Cambridge: Burleigh dodds, Science publishing; 2021. p. 281–347.

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in this article is granted. standing the behaviour and improving the welfare of pigs. Cambridge: Burleigh dodds, Science publishing; 2021. p. 281–347. Additional file 7: Tipping. The video shows a tipping pig. Permission to 7. Sutherland MA. Welfare implications of invasive piglet husbandry reuse the materials for the purpose of illustrating the signs and arguments procedures, methods of alleviation and alternatives: a review. N Z Vet J. of the authors in this article is granted. 2015;63(1):52–7. https://​doi.​org/​10.​1080/​00480​169.​2014.​961990. Additional file 8: Bending the spine. The picture shows a pig unburden 8. O’Connor A, Anthony R, Bergamasco L, Coetzee J, Gould S, Johnson AK, a hind leg by bending the spine. Permission to reuse the materials for et al. Pain management in the neonatal piglet during routine manage‑ the purpose of illustrating the signs and arguments of the authors in this ment procedures. Part 2: grading the quality of evidence and the article is granted. strength of recommendations. Anim Health Res Rev. 2014;15(1):39–62. https://​doi.​org/​10.​1017/​S1466​25231​40000​73. 9. Dzikamunhenga RS, Anthony R, Coetzee J, Gould S, Johnson A, Kar‑ Acknowledgements riker L, et al. Pain management in the neonatal piglet during routine Not applicable. management procedures. Part 1: a systematic review of randomized and non-randomized intervention studies. Anim Health Res Rev. Author contributions 2014;15(1):14–38. https://​doi.​org/​10.​1017/​S1466​25231​40000​61. JK designed, drafted, analysed, interpreted, revised, LT drafted, analysed, inter‑ 10. O’Connor A, Anthony R, Bergamasco L, Coetzee JF, Dzikamunhenga RS, preted, revised; KD revised, MM revised, JR drafted, revised, IE

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alysed, inter‑ 10. O’Connor A, Anthony R, Bergamasco L, Coetzee JF, Dzikamunhenga RS, preted, revised; KD revised, MM revised, JR drafted, revised, IE analysed, inter‑ Johnson AK, et al. Review: assessment of completeness of reporting in preted, revised, IHP revised, NK revised, LK revised, MW revised, SK analysed, intervention studies using livestock: an example from pain mitigation interpreted, revised, EGB designed, drafted, analysed, interpreted and revised. interventions in neonatal piglets. Animal. 2016;10(4):660–70. https://​ doi.​org/​10.​1017/​S1751​73111​50023​23. Funding 11. Contiero B, Cozzi G, Karpf L, Gottardo F. Pain in pig production: text Open Access funding enabled and organized by Projekt DEAL. This work is mining analysis of the scientific literature. J Agric Environ Ethics. financially funded by the German Federal Ministry of Food and Agriculture 2019;32(3):401–12. https://​doi.​org/​10.​1007/​s10806-​019-​09781-4. (BMEL) based on a decision of the Parliament of the Federal Republic of 12. Ison SH, Clutton RE, Di Giminiani P, Rutherford KM. A review of pain Germany, granted by the Federal Office for Agriculture and Food (BLE; grant assessment in pigs. Front Vet Sci. 2016;3:108. https://​doi.​org/​10.​3389/​ number 28N-2–008-01 "CARE-PIG"). fvets.​2016.​00108. 13. Hewson CJ, Dohoo IR, Lemke KA, Barkema HW. Canadian veterinarians’ Data availability use of analgesics in cattle, pigs, and horses in 2004 and 2005. Can Vet J. No datasets were generated or analysed during the current study. 2007;48(2):155–64. https://​doi.​org/​10.​4141/​cjas68-​021. 14. Council directive No 98/58/EC (CD) of 20 July 1998. Protection of animals kept for farming purposes., (14.12.2019). Declarations 15.

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