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((Short description|Overview about pain in animals))
((Use dmy dates|date=September 2020))
[[File:Carcharhinus galapagensis hooked.jpg|thumb|300px|right|A [[Galapagos shark]] hooked by a fishing boat]]

[[Pain]] negatively affects the health and welfare of animals.<ref>((Cite journal|last1=Mathews|first1=Karol|last2=Kronen|first2=Peter W|last3=Lascelles|first3=Duncan|last4=Nolan|first4=Andrea|last5=Robertson|first5=Sheilah|last6=Steagall|first6=Paulo VM|last7=Wright|first7=Bonnie|last8=Yamashita|first8=Kazuto|date=2014-05-20|title=Guidelines for Recognition, Assessment and Treatment of Pain|journal=Journal of Small Animal Practice|volume=55|issue=6|pages=E10–E68|doi=10.1111/jsap.12200|pmid=24841489|issn=0022-4510))</ref> "Pain" is defined by the [[International Association for the Study of Pain]] as "an unpleasant sensory and emotional experience associated with actual or potential [[Tissue (biology)|tissue]] damage, or described in terms of such damage."<ref name="IASPterms">((cite web|url=http://www.iasp-pain.org/Taxonomy?navItemNumber=576#Pain|title=IASP Pain Terminology|website=iasp-pain.org|access-date=3 May 2018|url-status=dead|archive-url=https://web.archive.org/web/20171109164229/https://www.iasp-pain.org/Taxonomy?navitemNumber=576#Pain|archive-date=9 November 2017))</ref> Only the animal experiencing the pain can know the pain's quality and intensity, and the degree of suffering. It is harder, if even possible, for an observer to know whether an emotional experience has occurred, especially if the sufferer cannot communicate.<ref>((Cite journal |url=https://www.academia.edu/1388768 |title=A Criticism of the IASP's Definition of Pain |access-date=2017-10-30 |url-status=live |archive-url=https://web.archive.org/web/20160822083728/http://www.academia.edu/1388768/A_Criticism_of_the_IASPs_Definition_of_Pain |archive-date=22 August 2016|last1=Wright |first1=Andrew ))</ref> Therefore, this concept is often excluded in definitions of '''pain in animals''', such as that provided by [[Michael Zimmerman (biologist)|Zimmerman]]: "an aversive sensory experience caused by actual or potential injury that elicits protective motor and vegetative reactions, results in learned avoidance and may modify species-specific behaviour, including social behaviour."<ref name="Zimmerman, (1986)">((cite journal | last1 = Zimmerman | first1 = M | year = 1986 | title = Physiological mechanisms of pain and its treatment | journal = Klinische Anaesthesiol Intensivether | volume = 32 | pages = 1–19 ))</ref> Nonhuman animals cannot report their feelings to language-using humans in the same manner as human communication, but observation of their behaviour provides a reasonable indication as to the extent of their pain. Just as with doctors and medics who sometimes share no common language with their patients, the indicators of pain can still be understood<!-- citation? -->.

According to the U.S. National Research Council Committee on Recognition and Alleviation of Pain in Laboratory Animals, pain is experienced by many animal [[species]], including [[mammals]] and possibly all [[vertebrates]].<ref>((cite web|url=https://www.ncbi.nlm.nih.gov/books/NBK32655/|title=Recognition and Alleviation of Pain in Laboratory Animals|author=National Research Council (US) Committee on Recognition and Alleviation of Pain in Laboratory Animals|publisher=[[National Center for Biotechnology Information]]|date=2009|access-date=14 February 2015|url-status=live|archive-url=https://web.archive.org/web/20170624072010/https://www.ncbi.nlm.nih.gov/books/NBK32655/|archive-date=24 June 2017))</ref> Overview of anatomy of the nervous system across animal kingdom indicates that, not only vertebrates, but also [[Pain in invertebrates|most invertebrates have the capacity to feel pain]].<ref>((Cite book |last=Ermak |first=Gennady |title=Plant-Based, Meat-Based and Between: Ways of Eating for Your Health and Our World |publisher=KDP |year=2022 |isbn=979-8785908680 |pages=55–65))</ref>

==The experience of pain==
Although there are numerous definitions of [[pain]], almost all involve two key components. First, [[nociception]] is required.<ref name="Sneddon, (2004)">((cite journal | last1 = Sneddon | first1 = L.U. | year = 2004 | title = Evolution of nociception in vertebrates: comparative analysis of lower vertebrates | url = https://animalstudiesrepository.org/acwp_vsm/43| journal = Brain Research Reviews | volume = 46 | issue = 2| pages = 123–130 | doi=10.1016/j.brainresrev.2004.07.007| pmid = 15464201 | s2cid = 16056461 ))</ref> This is the ability to detect noxious stimuli which evoke a [[reflex]] response that rapidly moves the entire animal, or the affected part of its body, away from the source of the stimulus. The concept of nociception does not imply any adverse, subjective "feeling" – it is a reflex action. An example in humans would be the rapid withdrawal of a finger that has touched something hot – the withdrawal occurs before any sensation of pain is actually experienced.

The second component is the experience of "pain" itself, or [[suffering]] – the internal, emotional interpretation of the nociceptive experience. Again in humans, this is when the withdrawn finger begins to hurt, moments after the withdrawal. Pain is therefore a private, emotional experience. Pain cannot be directly measured in other animals, including other humans; responses to putatively painful stimuli can be measured, but not the experience itself. To address this problem when assessing the capacity of other species to experience pain, argument-by-analogy is used. This is based on the principle that if an animal responds to a stimulus in a similar way to ourselves, it is likely to have had an analogous experience.

===Reflex response to painful stimuli===
[[File:Anatomy and physiology of animals A reflex arc.jpg|thumb|250px|right|Reflex arc of a dog when its paw is stuck with a pin. The spinal cord responds to signals from receptors in the paw, producing a reflex withdrawal of the paw. This localized response does not involve brain processes that might mediate a consciousness of pain, though these might also occur.]]
Nociception usually involves the transmission of a signal along [[nerve fiber]]s from the site of a noxious stimulus at the periphery to the spinal cord. Although this signal is also transmitted on to the brain, a [[reflex arc|reflex]] response, such as flinching or withdrawal of a limb, is produced by return signals originating in the spinal cord. Thus, both [[Physiology|physiological]] and behavioral responses to nociception can be detected, and no reference need be made to a conscious experience of pain. Based on such criteria, nociception has been observed in all major animal [[Taxon|taxa]].<ref name="Sneddon, (2004)"/>

===Awareness of pain===
Nerve impulses from nociceptors may reach the brain, where information about the stimulus (e.g. quality, location, and intensity), and effect (unpleasantness) are registered. Though the brain activity involved has been studied, the brain processes underlying conscious awareness are not well known.

==Adaptive value==

The [[Fitness (biology)|adaptive value]] of nociception is obvious; an organism detecting a noxious stimulus immediately withdraws the limb, appendage or entire body from the noxious stimulus and thereby avoids further (potential) injury. However, a characteristic of pain (in mammals at least) is that pain can result in [[hyperalgesia]] (a heightened sensitivity to noxious stimuli) and [[allodynia]] (a heightened sensitivity to non-noxious stimuli). When this heightened sensitisation occurs, the adaptive value is less clear. First, the pain arising from the heightened sensitisation can be disproportionate to the actual tissue damage caused. Second, the heightened sensitisation may also become chronic, persisting well beyond the tissues healing. This can mean that rather than the actual tissue damage causing pain, it is the pain due to the heightened sensitisation that becomes the concern. This means the sensitisation process is sometimes termed [[maladaptive]]. It is often suggested hyperalgesia and allodynia assist organisms to protect themselves during healing, but experimental evidence to support this has been lacking.<ref name="Price">((cite journal|author1=Price, T.J. |author2=Dussor, G. |name-list-style=amp |year=2014|title=Evolution: the advantage of 'maladaptive'pain plasticity|journal=Current Biology|volume=24|issue=10|pages=R384–R386 |doi=10.1016/j.cub.2014.04.011 |pmid=24845663 |pmc=4295114))</ref><ref name="Oxford">((Cite journal|url=http://www.oxfordreference.com/view/10.1093/oi/authority.20110803100128206|publisher=Oxford Reference|title=Maladaptive pain|access-date=16 May 2016|url-status=live|archive-url=https://web.archive.org/web/20160515151057/http://www.oxfordreference.com/view/10.1093/oi/authority.20110803100128206|archive-date=15 May 2016))</ref>

In 2014, the adaptive value of sensitisation due to injury was tested using the predatory interactions between [[longfin inshore squid]] (''Doryteuthis pealeii'') and [[black sea bass]] (''Centropristis striata'') which are natural predators of this squid. If injured squid are targeted by a bass, they began their defensive behaviours sooner (indicated by greater alert distances and longer flight initiation distances) than uninjured squid. If anaesthetic (1% ethanol and MgCl<sub>2</sub>) is administered prior to the injury, this prevents the sensitisation and blocks the behavioural effect. The authors claim this study is the first experimental evidence to support the argument that nociceptive sensitisation is actually an adaptive response to injuries.<ref name="Crooketal2014">((cite journal|author=Crook, R.J., Dickson, K., Hanlon, R.T. and Walters, E.T.|year=2014|title=Nociceptive sensitization reduces predation risk|journal=Current Biology|volume=24|issue=10|pages=1121–1125|doi=10.1016/j.cub.2014.03.043|pmid=24814149|doi-access=free))</ref>

==Argument-by-analogy==
To assess the capacity of other species to consciously suffer pain we resort to [[argument#Argument by analogy|argument-by-analogy]]. That is, if an animal responds to a stimulus the way a human does, it is likely to have had an analogous experience. If we stick a pin in a chimpanzee's finger and she rapidly withdraws her hand, we use argument-by-analogy and infer that like us, she felt pain. It might be argued that consistency requires us to infer, also, that a cockroach experiences conscious pain when it writhes after being stuck with a pin. The usual counter-argument is that although the physiology of consciousness is not understood, it clearly involves complex brain processes not present in relatively simple organisms.<ref name="Sherwin, 2001" /> Other analogies have been pointed out. For example, when given a choice of foods, rats<ref name="Colpaert et al., (2001)">((cite journal | last1 = Colpaert | first1 = F.C. | last2 = Tarayre | first2 = J.P. | last3 = Alliaga | first3 = M. | last4 = Slot | first4 = L.A.B. | last5 = Attal | first5 = N. | last6 = Koek | first6 = W. | year = 2001 | title = Opiate self-administration as a measure of chronic nociceptive pain in arthritic rats | journal = Pain | volume = 91 | issue = 1–2| pages = 33–45 | doi=10.1016/s0304-3959(00)00413-9| pmid = 11240076 | s2cid = 24858615 ))</ref> and chickens<ref name="Danbury et al., (2000)">((cite journal | last1 = Danbury | first1 = T.C. | last2 = Weeks | first2 = C.A. | last3 = Chambers | first3 = J.P. | last4 = Waterman-Pearson | first4 = A.E. | last5 = Kestin | first5 = S.C. | year = 2000 | title = Self-selection of the analgesic drug carprofen by lame broiler chickens | doi = 10.1136/vr.146.11.307 | pmid = 10766114 | journal = Veterinary Record | volume = 146 | issue = 11| pages = 307–311 | s2cid = 35062797 ))</ref> with clinical symptoms of pain will consume more of an analgesic-containing food than animals not in pain. Additionally, the consumption of the analgesic [[carprofen]] in lame chickens was positively correlated to the severity of lameness, and consumption resulted in an improved gait. Such [[anthropomorphism|anthropomorphic]] arguments face the criticism that physical reactions indicating pain may be neither the cause nor result of conscious states, and the approach is subject to criticism of anthropomorphic interpretation. For example, a single-celled organism such as an amoeba may writhe after being exposed to noxious stimuli despite the absence of nociception.

==History==
((see also|Animal consciousness))

The idea that animals might not experience [[pain]] or [[suffering]] as [[human being|humans]] do traces back at least to the 17th-century French philosopher, [[René Descartes]], who argued that animals lack [[consciousness]].<ref name=Carbone149>Carbone, Larry. '"What Animal Want: Expertise and Advocacy in Laboratory Animal Welfare Policy''. Oxford University Press, 2004, p. 149.</ref><ref name=nuffield45>[http://www.nuffieldbioethics.org/fileLibrary/pdf/RIA_Report_FINAL-opt.pdf The Ethics of research involving animals] Nuffield Council on Bioethics, Accessed 27 February 2008 ((webarchive |url=https://web.archive.org/web/20080227041442/http://www.nuffieldbioethics.org/fileLibrary/pdf/RIA_Report_FINAL-opt.pdf |date=27 February 2008 ))</ref><ref>Talking Point on the use of animals in scientific research, EMBO Reports 8, 6, 2007, pp. 521–525</ref> Researchers remained unsure into the 1980s as to whether animals experience pain, and veterinarians trained in the U.S. before 1989 were simply taught to ignore animal pain.<ref name=Rollin117>Rollin, Bernard. ''The Unheeded Cry: Animal Consciousness, Animal Pain, and Science''. New York: Oxford University Press, 1989, pp. xii, 117-118, cited in Carbone 2004, p. 150.</ref> In his interactions with scientists and other veterinarians, [[Bernard Rollin]] was regularly asked to "prove" that animals are conscious, and to provide "scientifically acceptable" grounds for claiming that they feel pain.<ref name=Rollin117/> Some authors say that the view that animals feel pain differently is now a minority view.<ref name=Carbone149/> Academic reviews of the topic are more equivocal, noting that, although it is likely that some animals have at least simple conscious thoughts and feelings,<ref>((cite journal | last1 = Griffin | first1 = DR | last2 = Speck | first2 = GB | title = New evidence of animal consciousness. | url = http://postcog.ucd.ie/files/fulltext.pdf | journal = Animal Cognition | volume = 7 | issue = 1 | pages = 5–18 | year = 2004 | pmid = 14658059 | doi = 10.1007/s10071-003-0203-x | s2cid = 8650837 | url-status = dead | archive-url = https://web.archive.org/web/20130121030113/http://postcog.ucd.ie/files/fulltext.pdf | archive-date = 21 January 2013))</ref> some authors continue to question how reliably animal mental states can be determined.<ref name=nuffield45/><ref>((cite journal | author = Allen C | year = 1998 | title = Assessing animal cognition: ethological and philosophical perspectives | url = http://www.journalofanimalscience.org/content/76/1/42.full.pdf | journal = J. Anim. Sci. | volume = 76 | issue = 1 | pages = 42–7 | pmid = 9464883 | doi = 10.2527/1998.76142x ))((Dead link|date=July 2020 |bot=InternetArchiveBot |fix-attempted=yes ))</ref>

==In different species==
The ability to experience pain in an animal, or another human for that matter, cannot be determined directly but it may be inferred through analogous physiological and behavioral reactions.<ref>((cite journal |vauthors=Abbott FV, Franklin KB, Westbrook RF |title=The formalin test: scoring properties of the first and second phases of the pain response in rats |journal=Pain |volume=60 |issue=1 |pages=91–102 |date=January 1995 |pmid=7715946 |doi=10.1016/0304-3959(94)00095-V|s2cid=35448280 ))</ref> Although many animals share similar mechanisms of pain detection to those of humans, have similar areas of the brain involved in processing pain, and show similar pain behaviours, it is notoriously difficult to assess how animals actually experience pain.<ref name=PAIN>((cite web|last=Sneddon|first=Lynne|title=Can animals feel pain?|url=http://www.wellcome.ac.uk/en/pain/microsite/culture2.html|publisher=PAIN|access-date=18 March 2012|url-status=dead|archive-url=https://web.archive.org/web/20120413122654/http://www.wellcome.ac.uk/en/pain/microsite/culture2.html|archive-date=13 April 2012))</ref>

===Nociception===
Nociceptive nerves, which preferentially detect (potential) injury-causing stimuli, have been identified in a variety of animals, including invertebrates. The medicinal [[leech]], ''[[Hirudo medicinalis]],'' and [[sea slug]] are classic model systems for studying nociception.<ref name=PAIN/> Many other vertebrate and invertebrate animals also show nociceptive reflex responses similar to our own.

===Pain===
Many animals also exhibit more complex behavioural and physiological changes indicative of the ability to experience pain: they eat less food, their normal behaviour is disrupted, their social behaviour is suppressed, they may adopt unusual behaviour patterns, they may emit characteristic distress calls, experience respiratory and cardiovascular changes, as well as inflammation and release of stress hormones.<ref name=PAIN/>

Some criteria that may indicate the potential of another species to feel pain include:<ref name = Elwood>((cite journal | last1 = Elwood | first1 = R.W. | last2 = Barr | first2 = S. | last3 = Patterson | first3 = L. | year = 2009 | title = Pain and stress in crustaceans? | journal = Applied Animal Behaviour Science | volume = 118 | issue = 3| pages = 128–136 | doi=10.1016/j.applanim.2009.02.018))</ref>
# Has a suitable [[nervous system]] and [[sensory receptor]]s
# Physiological changes to [[noxious stimuli]]
# Displays protective motor reactions that might include reduced use of an affected area such as limping, rubbing, holding or [[autotomy]]
# Has [[opioid receptor]]s and shows reduced responses to noxious stimuli when given [[analgesic]]s and [[local anaesthetic]]s
# Shows trade-offs between stimulus avoidance and other motivational requirements
# Shows [[avoidance learning]]
# High [[cognitive ability]] and [[sentience]]

==Vertebrates==

===Fish===
((Main|Pain in fish))

A typical human cutaneous nerve contains 83% [[Group C nerve fiber|C type trauma receptors]] (the type responsible for transmitting signals described by humans as excruciating pain); the same nerves in humans with [[congenital insensitivity to pain]] have only 24-28% C type receptors.<ref name=Rose2012>((cite journal | last1 = Rose | first1 = JD | last2 = Arlinghaus | first2 = R | last3 = Cooke | first3 = SJ | last4 = Diggles | first4 = BK | last5 = Sawynok | first5 = W | last6 = Stevens | first6 = ED|author-link7=Clive Wynne | last7 = Wynne | first7 = CDL | year = 2012 | title = Can fish really feel pain? | url = http://www.vapaa-ajankalastaja.fi/files/Tiedostot/RoseEtAl_FishFish_online_2012.pdf | journal = Fish and Fisheries | volume = 15 | issue = 1 | pages = 97–133 | doi = 10.1111/faf.12010 | url-status = live | archive-url = https://web.archive.org/web/20160304060805/http://www.vapaa-ajankalastaja.fi/files/Tiedostot/RoseEtAl_FishFish_online_2012.pdf | archive-date = 4 March 2016))</ref> The rainbow trout has about 5% C type fibres, while sharks and rays have 0%.<ref>((cite journal | last1 = Snow | first1 = P.J. | last2 = Plenderleith | first2 = M.B. | last3 = Wright | first3 = L.L. | year = 1993 | title = Quantitative study of primary sensory neurone populations of three species of elasmobranch fish | journal = Journal of Comparative Neurology | volume = 334 | issue = 1| pages = 97–103 | doi=10.1002/cne.903340108| pmid = 8408762 | s2cid = 32762031 ))</ref> Nevertheless, fish have been shown to have sensory neurons that are sensitive to damaging stimuli and are physiologically identical to human nociceptors.<ref name=fish_pain>((cite journal|last= L.U. Sneddon|title=Do fishes have nociceptors? Evidence for the evolution of a vertebrate sensory system.|display-authors=etal|pmc=1691351|pmid=12816648|doi=10.1098/rspb.2003.2349|volume=270|issue=1520|journal=Proc Biol Sci|pages=1115–21|year=2003))</ref> Behavioural and physiological responses to a painful event appear comparable to those seen in amphibians, birds, and mammals, and administration of an analgesic drug reduces these responses in fish.<ref>((cite journal | last1 = Sneddon | first1 = L.U. |name-list-style=vanc | year = 2009 | title = Pain and Distress in Fish | journal = Ilar J. | volume = 50 | issue = 4| pages = 338–342 | doi=10.1093/ilar.50.4.338| pmid = 19949250 | doi-access = free ))</ref>

Animal welfare advocates have raised concerns about the possible suffering of fish caused by angling. Some countries, e.g. Germany, have banned specific types of fishing, and the British [[RSPCA]] now formally prosecutes individuals who are cruel to fish.<ref name="timesonline.co.uk">((Cite news|url=http://www.thesundaytimes.co.uk/sto/news/uk_news/article35053.ece|author=Leake, J.|title=Anglers to Face RSPCA Check|newspaper=The Sunday Times|date=14 March 2004|access-date=15 September 2015|url-status=dead|archive-url=https://web.archive.org/web/20150923173418/http://www.thesundaytimes.co.uk/sto/news/uk_news/article35053.ece|archive-date=23 September 2015))</ref>

==Invertebrates==
((Main|Pain in invertebrates))
((Further|Pain in crustaceans))
Though it has been argued that most invertebrates do not feel pain,<ref name="Eisemann et al., 1984">((cite journal | last1 = Eisemann | first1 = C.H. | last2 = Jorgensen | first2 = W.K. | last3 = Rice | first3 = D.J. | last4 = Cribb | first4 = M.J. | last5 = Zalucki | first5 = M.P. | last6 = Merritt | first6 = B.W. | last7 = Webb | first7 = P.D. | name-list-style = vanc | year = 1984 | title = Do insects feel pain? - A biological view | url = http://nature.berkeley.edu/~kipwill/ESPM40_stuff/2011%20lec18%20Insect%20pain/Eisemann.pdf | journal = Experientia | volume = 40 | issue = 2| pages = 164–167 | doi = 10.1007/bf01963580 | s2cid = 3071 | url-status = dead | archive-url = https://web.archive.org/web/20130613011042/http://nature.berkeley.edu/~kipwill/ESPM40_stuff/2011%20lec18%20Insect%20pain/Eisemann.pdf | archive-date = 13 June 2013))</ref><ref>[https://sencanada.ca/content/sen/committee/372/lega/witn/shelly-e.htm "Do Invertebrates Feel Pain?"] ((webarchive|url=https://web.archive.org/web/20100106084119/https://sencanada.ca/content/sen/committee/372/lega/witn/shelly-e.htm |date=6 January 2010 )), The Senate Standing Committee on Legal and Constitutional Affairs, The [[Parliament of Canada]] Web Site, accessed 11 June 2008.</ref><ref>((cite journal |author=Jane A. Smith |title=A question of pain in invertebrates |journal=ILAR Journal |volume=33 |issue=1–2 |year=1991 |url=http://www.abolitionist.com/darwinian-life/invertebrate-pain.html |url-status=live |archive-url=https://web.archive.org/web/20111008212237/http://www.abolitionist.com/darwinian-life/invertebrate-pain.html |archive-date=8 October 2011))</ref> there is some evidence that invertebrates, especially the decapod [[crustacean]]s (e.g. crabs and lobsters) and [[cephalopod]]s (e.g. octopuses), exhibit behavioural and physiological reactions indicating they may have the capacity for this experience.<ref name="Sherwin, 2001">Sherwin, C.M. (2001). Can invertebrates suffer? Or, how robust is argument-by-analogy? ''Animal Welfare'', 10(supplement): 103-118</ref><ref name="Elwood, 2011">((cite journal | last1 = Elwood | first1 = R.W. | year = 2011 | title = Pain and suffering in invertebrates? | url = http://dels-old.nas.edu/ilar_n/ilarjournal/52_2/PDFs/v5202Elwood.pdf | journal = Institute of Laboratory Animal Resources Journal | volume = 52 | issue = 2 | pages = 175–84 | url-status = dead | archive-url = https://web.archive.org/web/20120407023813/http://dels-old.nas.edu/ilar_n/ilarjournal/52_2/PDFs/v5202Elwood.pdf | archive-date = 7 April 2012| doi = 10.1093/ilar.52.2.175 | pmid = 21709310 | doi-access = free ))</ref><ref name="Fiorito, 1986">((cite journal | last1 = Fiorito | first1 = G. | year = 1986 | title = Is there ''pain'' in invertebrates? | journal = Behavioural Processes | volume = 12 | issue = 4| pages = 383–388 | doi=10.1016/0376-6357(86)90006-9| pmid = 24924695 | s2cid = 26181117 ))</ref>
[[Nociceptor]]s have been found in [[nematode]]s, [[annelid]]s and [[mollusk]]s.<ref name ="St John Smith, et al., 2009">((cite journal | last1 = St John Smith | first1 = E. | last2 = Lewin | first2 = G.R. | year = 2009 | title = Nociceptors: a phylogenetic view | journal = Journal of Comparative Physiology A | volume = 195 | issue = 12| pages = 1089–1106 | doi=10.1007/s00359-009-0482-z| pmid = 19830434 | pmc = 2780683 ))</ref> Most insects do not possess nociceptors,<ref>((cite journal | doi = 10.1007/BF00489606 |vauthors=DeGrazia D, Rowan A | year = 1991 | title = Pain, suffering, and anxiety in animals and humans | journal = Theoretical Medicine and Bioethics | volume = 12 | issue = 3| pages = 193–211 | pmid=1754965|s2cid=34920699 ))</ref><ref>((cite journal | doi = 10.2307/3495093 | author = Lockwood JA | year = 1987 | title = The moral standing of insects and the ethics of extinction | journal = The Florida Entomologist | volume = 70 | issue = 1| pages = 70–89 | jstor = 3495093 ))</ref><ref>((cite journal |author1=Eisemann C. H. |author2=Jorgensen W. K. |author3=Merritt D. J. |author4=Rice M. J. |author5=Cribb B. W. |author6=Webb P. D. |author7=Zalucki M. P. | year = 1984 | title = Do insects feel pain? — A biological view | journal = Experientia | volume = 40 | issue = 2| pages = 164–7|doi=10.1007/bf01963580 |s2cid=3071 ))</ref> one known exception being the [[Drosophila melanogaster|fruit fly]].<ref>((cite journal | author = Tracey, J., W. Daniel, R. I. Wilson, G. Laurent, and S. Benzer. |date=2003 | title=''painless'', a ''Drosophila'' gene essential for nociception. |journal=Cell|volume= 113|pages= 261–273|doi= 10.1016/S0092-8674(03)00272-1 |pmid=12705873 |issue=2|s2cid=1424315 |doi-access=free ))</ref> In [[vertebrates]], endogenous [[opioid]]s are neurochemicals that moderate pain by interacting with opiate receptors. Opioid peptides and opiate receptors occur naturally in nematodes,<ref name="Wittenburg and Baumeister, 1999">((cite journal | last1 = Wittenburg | first1 = N. | last2 = Baumeister | first2 = R. | year = 1999 | title = Thermal avoidance in Caenorhabditis elegans: an approach to the study of nociception | journal = Proceedings of the National Academy of Sciences USA | volume = 96 | issue = 18| pages = 10477–10482 | doi=10.1073/pnas.96.18.10477| pmid = 10468634 | pmc = 17914 | bibcode = 1999PNAS...9610477W | doi-access = free ))</ref><ref name="Pryor et al., 2007">((cite journal | author = Pryor, S.C., Nieto, F., Henry, S. and Sarfo, J. | date= 2007|title= The effect of opiates and opiate antagonists on heat latency response in the parasitic nematode Ascaris suum. |journal = Life Sciences|volume=80| issue= 18|pages= 1650–1655 |doi=10.1016/j.lfs.2007.01.011 |pmid=17363006))</ref> mollusks,<ref name="Dalton andiddowson, 1989">((cite journal | last1 = Dalton | first1 = L.M. | last2 = Widdowson | first2 = P.S. | year = 1989 | title = The involvement of opioid peptides in stress-induced analgesia in the slug Arion ater | journal = Peptides | volume = 10 | issue = 1| pages = 9–13 | doi=10.1016/0196-9781(89)90067-3| pmid = 2568626 | s2cid = 26432057 ))</ref><ref name="Kavaliers and Ossenkopp, 1991">((cite journal | last1 = Kavaliers | first1 = M. | last2 = Ossenkopp | first2 = K.-P. | year = 1991 | title = Opioid systems and magnetic field effects in the land snail, Cepaea nemoralis | journal = Biological Bulletin | volume = 180 | issue = 2| pages = 301–309 | doi=10.2307/1542401| pmid = 29304689 | jstor = 1542401 | url = https://www.biodiversitylibrary.org/part/8589 ))</ref> insects<ref name="Dyakonova et al., 1999">((cite journal | last1 = Dyakonova | first1 = V.E. | last2 = Schurmann | first2 = F. | last3 = Sakharov | first3 = D.A. | year = 1999 | title = Effects of serotonergic and opioidergic drugs on escape behaviors and social status of male crickets | journal = Naturwissenschaften | volume = 86 | issue = 9| pages = 435–437 | doi=10.1007/s001140050647| pmid = 10501691 | bibcode = 1999NW.....86..435D | s2cid = 9466150 ))</ref><ref name="Zabala and Gomez, 1991">((cite journal | last1 = Zabala | first1 = N. | last2 = Gomez | first2 = M. | year = 1991 | title = Morphine analgesia, tolerance and addiction in the cricket, Pteronemobius | journal = Pharmacology Biochemistry and Behavior | volume = 40 | issue = 4| pages = 887–891 | doi=10.1016/0091-3057(91)90102-8| pmid = 1816576 | s2cid = 24429475 ))</ref> and crustaceans.<ref name="Lozada et al., 1988">((cite journal | last1 = Lozada | first1 = M. | last2 = Romano | first2 = A. | last3 = Maldonado | first3 = H. | year = 1988 | title = Effect of morphine and naloxone on a defensive response of the crab Chasmagnathus granulatus | journal = Pharmacology Biochemistry and Behavior | volume = 30 | issue = 3| pages = 635–640 | doi=10.1016/0091-3057(88)90076-7| pmid = 3211972 | s2cid = 45083722 ))</ref><ref name="Maldonado and Miralto, 1982">((cite journal | last1 = Maldonado | first1 = H. | last2 = Miralto | first2 = A. | year = 1982 | title = Effects of morphine and naloxone on a defensive response of the mantis shrimp (Squilla mantis) | journal = Journal of Comparative Physiology A | volume = 147 | issue = 4| pages = 455–459 | doi=10.1007/bf00612010| s2cid = 3013237 ))</ref> The presence of opioids in crustaceans has been interpreted as an indication that lobsters may be able to experience pain, although it has been claimed "at present no certain conclusion can be drawn".<ref name="Sømme">((cite journal |author=L. Sømme |year=2005 |title=Sentience and pain in invertebrates: Report to Norwegian Scientific Committee for Food Safety |journal=Norwegian University of Life Sciences, Oslo))</ref>

One suggested reason for rejecting a pain experience in invertebrates is that invertebrate brains are too small. However, brain size does not necessarily equate to complexity of function.<ref name="Chittka and Niven, 2009">((Cite journal | last1 = Chittka | first1 = L. | last2 = Niven | first2 = J. | doi = 10.1016/j.cub.2009.08.023 | title = Are Bigger Brains Better? | journal = Current Biology | volume = 19 | issue = 21 | pages = R995–R1008 | year = 2009 | pmid =  19922859| s2cid = 7247082 | doi-access = free ))</ref> Moreover, weight for body-weight, the [[cephalopod]] brain is in the same size bracket as the vertebrate brain, smaller than that of birds and mammals, but as big as or bigger than most fish brains.<ref>((cite web|url=http://malankazlev.com/kheper/topics/intelligence/cephalopod_brainsize.html|title=Cephalopod brain size|website=malankazlev.com|access-date=8 April 2020))</ref><ref>((cite journal | last1 = Packard | first1 = A | year = 1972 | title = Cephalopods and fish: the limits of convergence | journal = Biological Reviews | volume = 47 | issue = 2| pages = 241–307 [266–7] | doi=10.1111/j.1469-185X.1972.tb00975.x| s2cid = 85088231 ))</ref> Remarkably, as demonstrated by cognitive tests, intelligence of cephalopods is comparable to that of five-year-old human children.<ref>((Cite book |last=Ermak |first=Gennady |title=Plant-Based, Meat-Based and Between: Ways of Eating for Your Health and Our World |publisher=KDP |year=2022 |isbn=979-8785908680 |pages=62))</ref>

Since September 2010, all cephalopods being used for scientific purposes in the EU are protected by EU Directive 2010/63/EU which states "...there is scientific evidence of their [cephalopods] ability to experience pain, suffering, distress and lasting harm.<ref name="EUdirective">((cite web|title=Directive 2010/63/EU of the European Parliament and of the Council|url=http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2010:276:0033:0079:EN:PDF|publisher=Official Journal of the European Union|access-date=17 April 2016|at=Article 1, 3(b)))</ref> In the UK, animal protection legislation<ref name="ASPA1986">((cite web|url=http://www.legislation.gov.uk/ukpga/1986/14/contents|title=Animals (Scientific Protection) Act 1986|access-date=18 April 2016|url-status=live|archive-url=https://web.archive.org/web/20160412220012/http://www.legislation.gov.uk/ukpga/1986/14/contents|archive-date=12 April 2016))</ref> means that cephalopods used for scientific purposes must be killed humanely, according to prescribed methods (known as "Schedule 1 methods of euthanasia") known to minimise suffering.<ref name="Schedule 1">((cite web|url=http://www.legislation.gov.uk/uksi/2012/3039/schedule/1/made|access-date=15 April 2016|title=The Animals (Scientific Procedures) Act 1986 Amendment Regulations 2012|url-status=live|archive-url=https://web.archive.org/web/20160211121110/http://www.legislation.gov.uk/uksi/2012/3039/schedule/1/made|archive-date=11 February 2016))</ref>

==In medicine and research==

===Veterinary medicine===
[[Veterinary medicine]] uses, for actual or potential animal pain, the same [[analgesic]]s and [[anesthetic]]s as used in humans.<ref>((cite journal |vauthors=Viñuela-Fernández I, Jones E, Welsh EM, Fleetwood-Walker SM |title=Pain mechanisms and their implication for the management of pain in farm and companion animals |journal=Vet. J. |volume=174 |issue=2 |pages=227–39 |date=September 2007 |pmid=17553712 |doi=10.1016/j.tvjl.2007.02.002))</ref>

===Dolorimetry===
[[Dolorimeter|Dolorimetry]] (''dolor'': Latin: pain, grief) is the measurement of the pain response in animals, including humans. It is practiced occasionally in medicine, as a diagnostic tool, and is regularly used in research into the basic science of pain, and in testing the efficacy of analgesics. 

The intense [[sociality]] of humans and the readiness with which they perceive, and [[Empathy|identify]] with, manifestations of physical pain in others have made the study of pain notoriously difficult to quantify. Indeed, many investigators of animal pain shy away from use of the word "pain" in published research. They consider the term to be unscientific and grounded in human emotion, preferring others such as "stress" or "avoidance". As the subjective experience of animals is very resistant to rational assessment, the subjective difference between their painless reflex responses to noxious stimuli ([[nociception]]) and pain as humans understand it has been nearly impossible to determine conclusively.

For this reason essentially all scientific research into the nature of animal pain has depended upon so-called pain proxies. These include obvious [[Ethology|behavioral changes]]—shying away, stamping, vocalization, ear cues etc.— as well as subtler changes, as when injured chickens or rats choose feed that has been laced with an analgesic over feed that has not. Most prized by scientists are the quantifiable physiological changes such as elevated [[heart rate]] or [[stress hormone]] [[Serum (blood)|serum]] concentrations. These physiological proxies are valued because their assessments are carried out by machines and do not rely on humans to determine the magnitude of the variable under study. This is seldom the case for behavioral pain proxies, which are most often scored by a researcher on some numerical scale ranging from "no response" to "intense response".<ref>((Cite journal |last1=Danbury |first1=T. C. |last2=Weeks |first2=C. A. |last3=Waterman-Pearson |first3=A. E. |last4=Kestin |first4=S. C. |last5=Chambers |first5=J. P. |date=March 2000 |title=Self-selection of the analgesic drug carprofen by lame broiler chickens |url=http://doi.wiley.com/10.1136/vr.146.11.307 |journal=Veterinary Record |language=en |volume=146 |issue=11 |pages=307–311 |doi=10.1136/vr.146.11.307|pmid=10766114 |s2cid=35062797 ))</ref>

==== Dolormetric methods in animals ====
Nonhuman animal pain measurement techniques include the [[Randall-Selitto test|paw pressure test]], [[tail flick test]], [[hot plate test]] and [[Grimace scale (animals)|grimace scales]]. Grimace scales are used to assess post-operative and disease pain in mammals. Scales have been developed for ten mammalian species such as mice, rats, and rabbits.<ref>((Cite journal|last1=Mogil|first1=Jeffrey S.|last2=Pang|first2=Daniel S. J.|last3=Silva Dutra|first3=Gabrielle Guanaes|last4=Chambers|first4=Christine T.|date=2020-09-01|title=The development and use of facial grimace scales for pain measurement in animals|url=http://www.sciencedirect.com/science/article/pii/S0149763420304747|journal=Neuroscience & Biobehavioral Reviews|language=en|volume=116|pages=480–493|doi=10.1016/j.neubiorev.2020.07.013|pmid=32682741|s2cid=220575703|issn=0149-7634))</ref> Dale Langford established and published the Mouse Grimace Scale in 2010,<ref>((Cite journal|last1=Langford|first1=Dale J.|last2=Bailey|first2=Andrea L.|last3=Chanda|first3=Mona Lisa|last4=Clarke|first4=Sarah E.|last5=Drummond|first5=Tanya E.|last6=Echols|first6=Stephanie|last7=Glick|first7=Sarah|last8=Ingrao|first8=Joelle|last9=Klassen-Ross|first9=Tammy|last10=LaCroix-Fralish|first10=Michael L.|last11=Matsumiya|first11=Lynn|date=2010|title=Coding of facial expressions of pain in the laboratory mouse|url=https://www.nature.com/articles/nmeth.1455|journal=Nature Methods|language=en|volume=7|issue=6|pages=447–449|doi=10.1038/nmeth.1455|pmid=20453868|s2cid=16703705|issn=1548-7105))</ref> with Susana Sotocinal inventing the Rat Grimace Scale a year later in 2011.<ref>((Cite journal|last1=Sotocina|first1=Susana G|last2=Sorge|first2=Robert E|last3=Zaloum|first3=Austin|last4=Tuttle|first4=Alexander H|last5=Martin|first5=Loren J|last6=Wieskopf|first6=Jeffrey S|last7=Mapplebeck|first7=Josiane CS|last8=Wei|first8=Peng|last9=Zhan|first9=Shu|last10=Zhang|first10=Shuren|last11=McDougall|first11=Jason J|date=2011-08-05|title=The Rat Grimace Scale: A Partially Automated Method for Quantifying Pain in the Laboratory Rat via Facial Expressions|journal=Molecular Pain|language=en|volume=7|pages=1744–8069–7-55|doi=10.1186/1744-8069-7-55|pmid=21801409|pmc=3163602|issn=1744-8069|doi-access=free))</ref> Using video stills from recorders, researchers can track changes in an animal's positioning of ears and whiskers, orbital tightening, and bulging or flattening of the nose area, and match these images against the images in the grimace scale.<ref>((Cite web|title=Grimace scales|url=https://www.nc3rs.org.uk/grimacescales|access-date=December 10, 2020|website=National Centre for the Replacement Refinement and Reduction of Animals in Research (NC3Rs).))</ref> Laboratory researcher and veterinarians may use the grimace scales to evaluate when to administer analgesia to an animal or whether severity of pain warrants a humane endpoint ([[euthanasia]]) or the animal in a study.

===Laboratory animals===
((See also|Animal testing regulations))
Animals are kept in laboratories for a wide range of reasons, some of which may involve pain, suffering or distress, whilst others (e.g. many of those involved in breeding) will not. The extent to which [[animal testing]] causes pain and suffering in laboratory animals is the subject of much debate.<ref>((cite journal | url = http://jas.fass.org/cgi/pmidlookup?view=long&pmid=1808195 | pmid = 1808195 | volume = 69 | issue = 12 | title = The implications of cognitive processes for animal welfare | date = December 1991 | journal = J. Anim. Sci. | pages = 5017–22 | last1 = Duncan | first1 = IJ | last2 = Petherick | first2 = JC | doi = 10.2527/1991.69125017x ))((dead link|date=March 2018 |bot=InternetArchiveBot |fix-attempted=yes )); ((cite journal | last1 = Curtis | first1 = SE | last2 = Stricklin | first2 = WR | year = 1991 | title = The importance of animal cognition in agricultural animal production systems: an overview | url = http://jas.fass.org/cgi/pmidlookup?view=long&pmid=1808193 | journal = J. Anim. Sci. | volume = 69 | issue = 12 | pages = 5001–7 | pmid = 1808193 | doi = 10.2527/1991.69125001x ))((dead link|date=March 2018 |bot=InternetArchiveBot |fix-attempted=yes ))</ref> [[Marian Stamp Dawkins]] defines "suffering" in laboratory animals as the experience of one of "a wide range of extremely unpleasant subjective (mental) states."<ref name=StampDawkins>[[Marian Stamp Dawkins|Stamp Dawkins, Marian]]. "Scientific Basis for Assessing Suffering in Animals," in [[Peter Singer|Singer, Peter]]. ''In Defense of Animals: The Second Wave''. Blackwell, 2006. p. 28.</ref> The [[U.S. National Research Council]] has published guidelines on the care and use of laboratory animals,<ref>((cite report|url=http://www.nap.edu/openbook.php?record_id=12910|date=2011|publisher=The National Academies Press|editor=Committee for the Update of the Guide for the Care and Use of Laboratory Animals|title=Guide for the Care and Use of Laboratory Animals|edition=8th|url-status=live|archive-url=https://web.archive.org/web/20130801084814/http://www.nap.edu/openbook.php?record_id=12910|archive-date=1 August 2013))</ref> as well as a report on recognizing and alleviating pain in [[vertebrates]].<ref>((cite report|url=http://ntp.niehs.nih.gov/NTP/About_NTP/SACATM/2009/June/NRCRecPainLabAnimals12526_508.pdf|title=Recognition and Alleviation of Pain in Laboratory Animals|publisher=The National Academies Press|author=[[United States National Research Council|National Research Council]], Division on Earth and Life Studies, Committee on Recognition and Alleviation of Pain in Laboratory Animals|date=2009|url-status=dead|archive-url=https://web.archive.org/web/20131103154553/http://ntp.niehs.nih.gov/NTP/About_NTP/SACATM/2009/June/NRCRecPainLabAnimals12526_508.pdf|archive-date=3 November 2013))</ref> The [[United States Department of Agriculture]] defines a "painful procedure" in an animal study as one that would "reasonably be expected to cause more than slight or momentary pain or distress in a human being to which that procedure was applied."<ref name=USDApaindef>[http://www.nal.usda.gov/awic/newsletters/v11n1/11n19cfr.htm Animal Welfare; Definitions for and Reporting of Pain and Distress"] ((webarchive|url=https://web.archive.org/web/20141006071514/http://www.nal.usda.gov/awic/newsletters/v11n1/11n19cfr.htm |date=6 October 2014 )), Animal Welfare Information Center Bulletin, Summer 2000, Vol. 11 No. 1-2, United States Department of Agriculture.</ref> Some critics argue that, paradoxically, researchers raised in the era of increased awareness of [[animal welfare]] may be inclined to deny that animals are in pain simply because they do not want to see themselves as people who inflict it.<ref>Carbone 2004, p. 151.</ref> PETA however argues that there is no doubt about animals in laboratories being inflicted with pain.<ref>((cite web|url=http://www.peta.org/issues/animals-used-for-experimentation/animals-in-laboratories.aspx|title=Cruelty to Animals in Laboratories|website=peta.org|date=22 June 2010 |access-date=3 May 2018|url-status=live|archive-url=https://web.archive.org/web/20131102211947/http://www.peta.org/issues/animals-used-for-experimentation/animals-in-laboratories.aspx|archive-date=2 November 2013))</ref> In the UK, animal research likely to cause "pain, suffering, distress or lasting harm" is regulated by the [[Animals (Scientific Procedures) Act 1986]] and research with the potential to cause pain is regulated by the [[Animal Welfare Act of 1966]] in the US.

In the U.S., researchers are not required to provide laboratory animals with pain relief if the administration of such drugs would interfere with their experiment. Laboratory animal veterinarian Larry Carbone writes, "Without question, present public policy allows humans to cause laboratory animals unalleviated pain. The AWA, the ''Guide for the Care and Use of Laboratory Animals'', and current Public Health Service policy all allow for the conduct of what are often called 'Category E' studies – experiments in which animals are expected to undergo significant pain or distress that will be left untreated because treatments for pain would be expected to interfere with the experiment."<ref>((cite journal|last1=Carbone|first1=L|title=Pain in Laboratory Animals: The Ethical and Regulatory Imperatives|journal=PLOS ONE|date=7 September 2011|volume=6|issue=9|pages=e21578|doi=10.1371/journal.pone.0021578|pmid=21915253|pmc=3168441|bibcode=2011PLoSO...621578C|doi-access=free))</ref>

==== Severity scales ====

Eleven countries have national classification systems of pain and suffering experienced by animals used in research: Australia, Canada, Finland, Germany, The Republic of Ireland, The Netherlands, New Zealand, Poland, Sweden, Switzerland, and the UK. The US also has a mandated national scientific animal-use classification system, but it is markedly different from other countries in that it reports on whether pain-relieving drugs were required and/or used.<ref name="Fenwick et al., 2011">((cite journal | last1 = Fenwick | first1 = N. | last2 = Ormandy | first2 = E. | last3 = Gauthier | first3 = C. | last4 = Griffin | first4 = G. | year = 2011 | title = Classifying the severity of scientific animal use: a review of international systems | journal = Animal Welfare | volume = 20 | issue = 2 | pages = 281–301 | doi = 10.1017/S0962728600002761 | s2cid = 70934694 ))</ref> The first severity scales were implemented in 1986 by Finland and the UK. The number of severity categories ranges between 3 (Sweden and Finland) and 9 (Australia). In the UK, research projects are classified as "mild", "moderate", and "substantial" in terms of the suffering the researchers conducting the study say they may cause; a fourth category of "unclassified" means the animal was anesthetized and killed without recovering consciousness. It should be remembered that in the UK system, many research projects (e.g. transgenic breeding, feeding distasteful food) will require a license under the [[Animals (Scientific Procedures) Act 1986]], but may cause little or no pain or suffering. In December 2001, 39 percent (1,296) of project licenses in force were classified as "mild", 55 percent (1,811) as "moderate", two percent (63) as "substantial", and 4 percent (139) as "unclassified".<ref name=RyderSinger>[[Richard D. Ryder|Ryder, Richard D.]] "Speciesism in the laboratory, " in [[Peter Singer|Singer, Peter]]. ''In Defense of Animals: The Second Wave''. Blackwell, 2006. p. 99.</ref> In 2009, of the project licenses issued, 35 percent (187) were classified as "mild", 61 percent (330) as "moderate", 2 percent (13) as "severe" and 2 percent (11) as unclassified.<ref>((cite web|url=http://www.homeoffice.gov.uk/publications/science-research-statistics/research-statistics/science-research/spanimals09/spanimals09?view=Binary|archive-url=http://webarchive.nationalarchives.gov.uk/20110922113036/http://www.homeoffice.gov.uk/publications/science-research-statistics/research-statistics/science-research/spanimals09/spanimals09?view=Binary|url-status=dead|archive-date=22 September 2011|title=Home Office Statistics |access-date=31 October 2011))</ref>

In the US, the ''Guide for the Care and Use of Laboratory Animals'' defines the parameters for animal testing regulations. It states, "The ability to experience and respond to pain is widespread in the animal kingdom...Pain is a stressor and, if not relieved, can lead to unacceptable levels of stress and distress in animals."<ref>Guide for the Care and Use of Laboratory Animals, ILAR, National Research Council, 1996 copyright, p. 64</ref> The ''Guide'' states that the ability to recognize the symptoms of pain in different species is essential for the people caring for and using animals. Accordingly, all issues of animal pain and distress, and their potential treatment with analgesia and anesthesia, are required regulatory issues for [[Institutional Animal Care and Use Committee|animal protocol approval]].

==See also==
((Portal|Animals))
((div col|colwidth=30em))
* [[Animal ethics]]
* [[Animal cognition]]
* [[Animal welfare]]
* [[Animal welfare science]]
* [[Bridge locus]]
* [[Animal consciousness]]
* [[Cruelty to animals]]
* [[Emotion in animals]]
* [[Ethics of uncertain sentience]]
* [[List of mutilatory procedures on animals]]
* [[Psychology of eating meat]]
* [[Moral status of animals in the ancient world]]
* [[Neural correlates of consciousness]]
* [[Philosophy of mind]]
* [[Three Rs (animal research)]]
* [[Wild animal suffering]]
((div col end))

==References==
((reflist|30em))

==External links==
* Animal Ethics [https://www.animal-ethics.org/sentience-section/animal-sentience/indicators-animal-suffering "Indicators of animal suffering"] ((Webarchive|url=https://web.archive.org/web/20220117001343/https://www.animal-ethics.org/sentience-section/animal-sentience/indicators-animal-suffering/ |date=17 January 2022 )), ''Animal Sentience''.
* Kent, J. E. & Molony, V. [http://www.vet.ed.ac.uk/animalpain/ ''Guidelines on the Recognition and Assessment of Pain in Animals'']
* Crawford, R. [https://web.archive.org/web/20200219190144/https://pdfs.semanticscholar.org/a3e4/426f680f7eac078fe5a536b83f5aa7f73947.pdf ''A Reference Source for the Recognition & Alleviation of Pain & Distress in Animals''], United States Department of Agriculture.
* [https://www.nal.usda.gov/awic/recognition-and-assessment <nowiki>Recognition and Assessment [of Pain]</nowiki>], Animal Welfare Information Center (USDA)
((animal cognition))
((animal rights))
((animal welfare))
((ethology))

[[Category:Pain in animals| ]]
[[Category:Animal emotions]]
[[Category:Cruelty to animals]]

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