Pain and suffering in laboratory animals
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Pain Pain is a distressing feeling often caused by intense or damaging stimuli. The International Association for the Study of Pain defines pain as "an unpleasant sensory and emotional experience associated with, or resembling that associated with, ...
negatively affects the health and welfare of animals. "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 damage, or described in terms of such damage." 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. Therefore, this concept is often excluded in definitions of pain in animals, such as that provided by 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." 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. 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. Overview of anatomy of the nervous system across animal kingdom indicates that, not only vertebrates, but also most of invertebrates have the capacity to feel pain.


The experience of pain

Although there are numerous definitions of
pain Pain is a distressing feeling often caused by intense or damaging stimuli. The International Association for the Study of Pain defines pain as "an unpleasant sensory and emotional experience associated with, or resembling that associated with, ...
, almost all involve two key components. First,
nociception Nociception (also nocioception, from Latin ''nocere'' 'to harm or hurt') is the sensory nervous system's process of encoding noxious stimuli. It deals with a series of events and processes required for an organism to receive a painful stimulus, co ...
is required. This is the ability to detect noxious stimuli which evoke a
reflex In biology, a reflex, or reflex action, is an involuntary, unplanned sequence or action and nearly instantaneous response to a stimulus. Reflexes are found with varying levels of complexity in organisms with a nervous system. A reflex occurs ...
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 Suffering, or pain in a broad sense, may be an experience of unpleasantness or aversion, possibly associated with the perception of harm or threat of harm in an individual. Suffering is the basic element that makes up the negative valence of a ...
– 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

Nociception usually involves the transmission of a signal along
nerve fiber An axon (from Greek ἄξων ''áxōn'', axis), or nerve fiber (or nerve fibre: see spelling differences), is a long, slender projection of a nerve cell, or neuron, in vertebrates, that typically conducts electrical impulses known as action po ...
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 In biology, a reflex, or reflex action, is an involuntary, unplanned sequence or action and nearly instantaneous response to a stimulus. Reflexes are found with varying levels of complexity in organisms with a nervous system. A reflex occurs ...
response, such as flinching or withdrawal of a limb, is produced by return signals originating in the spinal cord. Thus, both
physiological Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chemical ...
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 taxa.


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
adaptive value The adaptive value represents the combined influence of all characters which affect the fitness of an individual or population. Definition Adaptive value is an essential concept of population genetics. It represents usefulness of a trait that c ...
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. In 2014, the adaptive value of sensitisation due to injury was tested using the predatory interactions between
longfin inshore squid The longfin inshore squid (''Doryteuthis pealeii'') is a species of squid of the family Loliginidae. Description This species of squid is often seen with a reddish hue, but like many types of squid can manipulate its color, varying from a deep ...
(''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 MgCl2) 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.


Argument-by-analogy

To assess the capacity of other species to consciously suffer pain we resort to 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 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. Other analogies have been pointed out. For example, when given a choice of foods, rats and chickens 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
anthropomorphic Anthropomorphism is the attribution of human traits, emotions, or intentions to non-human entities. It is considered to be an innate tendency of human psychology. Personification is the related attribution of human form and characteristics t ...
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

The idea that animals might not experience
pain Pain is a distressing feeling often caused by intense or damaging stimuli. The International Association for the Study of Pain defines pain as "an unpleasant sensory and emotional experience associated with, or resembling that associated with, ...
or
suffering Suffering, or pain in a broad sense, may be an experience of unpleasantness or aversion, possibly associated with the perception of harm or threat of harm in an individual. Suffering is the basic element that makes up the negative valence of a ...
as humans do traces back at least to the 17th-century French philosopher, René Descartes, who argued that animals lack consciousness.Carbone, Larry. '"What Animal Want: Expertise and Advocacy in Laboratory Animal Welfare Policy''. Oxford University Press, 2004, p. 149.The Ethics of research involving animals
Nuffield Council on Bioethics, Accessed 27 February 2008
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.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. In his interactions with scientists and other veterinarians,
Bernard Rollin Bernard Elliot Rollin (February 18, 1943 – November 19, 2021) was an American philosopher, who was emeritus professor of philosophy, animal sciences, and biomedical sciences at Colorado State University. He was considered to be the "father of ...
was regularly asked to "prove" that animals are conscious, and to provide "scientifically acceptable" grounds for claiming that they feel pain. Some authors say that the view that animals feel pain differently is now a minority view. 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, some authors continue to question how reliably animal mental states can be determined.


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. 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.


Nociception

Nociceptive nerves, which preferentially detect (potential) injury-causing stimuli, have been identified in a variety of animals, including invertebrates. The medicinal
leech Leeches are segmented parasitic or predatory worms that comprise the subclass Hirudinea within the phylum Annelida. They are closely related to the oligochaetes, which include the earthworm, and like them have soft, muscular segmented bodie ...
, '' Hirudo medicinalis,'' and sea slug are classic model systems for studying nociception. 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. Some criteria that may indicate the potential of another species to feel pain include: # Has a suitable nervous system and
sensory receptor Sensory neurons, also known as afferent neurons, are neurons in the nervous system, that convert a specific type of stimulus, via their receptors, into action potentials or graded potentials. This process is called sensory transduction. The cell ...
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 receptors and shows reduced responses to noxious stimuli when given
analgesic An analgesic drug, also called simply an analgesic (American English), analgaesic (British English), pain reliever, or painkiller, is any member of the group of drugs used to achieve relief from pain (that is, analgesia or pain management). It ...
s and
local anaesthetic A local anesthetic (LA) is a medication that causes absence of pain sensation. In the context of surgery, a local anesthetic creates an absence of pain in a specific location of the body without a loss of consciousness, as opposed to a general an ...
s # Shows trade-offs between stimulus avoidance and other motivational requirements # Shows
avoidance learning An avoidance response is a natural adaptive behavior performed in response to danger. Excessive avoidance has been suggested to contribute to anxiety disorders, leading psychologists and neuroscientists to study how avoidance behaviors are learned u ...
# High
cognitive ability Cognitive skills, also called cognitive functions, cognitive abilities or cognitive capacities, are brain-based skills which are needed in acquisition of knowledge, manipulation of information and reasoning. They have more to do with the mechanisms ...
and
sentience Sentience is the capacity to experience feelings and sensations. The word was first coined by philosophers in the 1630s for the concept of an ability to feel, derived from Latin '':wikt:sentientem, sentientem'' (a feeling), to distinguish it fro ...


Vertebrates


Fish

A typical human cutaneous nerve contains 83% 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. The rainbow trout has about 5% C type fibres, while sharks and rays have 0%. Nevertheless, fish have been shown to have sensory neurons that are sensitive to damaging stimuli and are physiologically identical to human nociceptors. 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. 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.


Invertebrates

Though it has been argued that most invertebrates do not feel pain, there is some evidence that invertebrates, especially the decapod crustaceans (e.g. crabs and lobsters) and
cephalopod A cephalopod is any member of the molluscan class Cephalopoda (Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head ...
s (e.g. octopuses), exhibit behavioural and physiological reactions indicating they may have the capacity for this experience.Sherwin, C.M. (2001). Can invertebrates suffer? Or, how robust is argument-by-analogy? ''Animal Welfare'', 10(supplement): 103-118 Nociceptors have been found in
nematode The nematodes ( or grc-gre, Νηματώδη; la, Nematoda) or roundworms constitute the phylum Nematoda (also called Nemathelminthes), with plant-Parasitism, parasitic nematodes also known as eelworms. They are a diverse animal phylum inhab ...
s,
annelid The annelids (Annelida , from Latin ', "little ring"), also known as the segmented worms, are a large phylum, with over 22,000 extant species including ragworms, earthworms, and leeches. The species exist in and have adapted to various ecol ...
s and mollusks. Most insects do not possess nociceptors, one known exception being the fruit fly. In vertebrates, endogenous opioids are neurochemicals that moderate pain by interacting with opiate receptors. Opioid peptides and opiate receptors occur naturally in nematodes, mollusks, insects and crustaceans. 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". 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. Moreover, weight for body-weight, the
cephalopod A cephalopod is any member of the molluscan class Cephalopoda (Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head ...
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. Remarkably, as demonstrated by cognitive tests, intelligence of cephalopods is comparable to that of five-year-old human children. 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 ephalopodsability to experience pain, suffering, distress and lasting harm. In the UK, animal protection legislation 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.


In medicine and research


Veterinary medicine

Veterinary medicine uses, for actual or potential animal pain, the same
analgesic An analgesic drug, also called simply an analgesic (American English), analgaesic (British English), pain reliever, or painkiller, is any member of the group of drugs used to achieve relief from pain (that is, analgesia or pain management). It ...
s and anesthetics as used in humans.


Dolorimetry

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 Sociality is the degree to which individuals in an animal population tend to associate in social groups (gregariousness) and form cooperative societies. Sociality is a survival response to evolutionary pressures. For example, when a mother wasp ...
of humans and the readiness with which they perceive, and 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 Nociception (also nocioception, from Latin ''nocere'' 'to harm or hurt') is the sensory nervous system's process of encoding noxious stimuli. It deals with a series of events and processes required for an organism to receive a painful stimulus, co ...
) 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 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 Serum may refer to: *Serum (blood), plasma from which the clotting proteins have been removed **Antiserum, blood serum with specific antibodies for passive immunity * Serous fluid, any clear bodily fluid * Truth serum, a drug that is likely to mak ...
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".


Dolormetric methods in animals

Nonhuman animal pain measurement techniques include the paw pressure test, tail flick test, hot plate test and 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. Dale Langford established and published the Mouse Grimace Scale in 2010, with Susana Sotocinal inventing the Rat Grimace Scale a year later in 2011. Using video stills from recorders, researchers can track changes in an animal's the 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. 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 Euthanasia (from el, εὐθανασία 'good death': εὖ, ''eu'' 'well, good' + θάνατος, ''thanatos'' 'death') is the practice of intentionally ending life to eliminate pain and suffering. Different countries have different eut ...
) or the animal in a study.


Laboratory animals

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. Marian Stamp Dawkins defines "suffering" in laboratory animals as the experience of one of "a wide range of extremely unpleasant subjective (mental) states." Stamp Dawkins, Marian. "Scientific Basis for Assessing Suffering in Animals," in Singer, Peter. ''In Defense of Animals: The Second Wave''. Blackwell, 2006. p. 28. The
U.S. National Research Council The National Academies of Sciences, Engineering, and Medicine (also known as NASEM or the National Academies) are the collective scientific national academy of the United States. The name is used interchangeably in two senses: (1) as an umbrell ...
has published guidelines on the care and use of laboratory animals, as well as a report on recognizing and alleviating pain in vertebrates. 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."Animal Welfare; Definitions for and Reporting of Pain and Distress"
, Animal Welfare Information Center Bulletin, Summer 2000, Vol. 11 No. 1-2, United States Department of Agriculture.
Some critics argue that, paradoxically, researchers raised in the era of increased awareness of
animal welfare Animal welfare is the well-being of non-human animals. Formal standards of animal welfare vary between contexts, but are debated mostly by animal welfare groups, legislators, and academics. Animal welfare science uses measures such as longevity ...
may be inclined to deny that animals are in pain simply because they do not want to see themselves as people who inflict it. PETA however argues that there is no doubt about animals in laboratories being inflicted with pain. 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."


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. 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". Ryder, Richard D. "Speciesism in the laboratory, " in Singer, Peter. ''In Defense of Animals: The Second Wave''. Blackwell, 2006. p. 99. 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. 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."Guide for the Care and Use of Laboratory Animals, ILAR, National Research Council, 1996 copyright, p. 64 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 animal protocol approval.


See also

*
Animal ethics Animal ethics is a branch of ethics which examines human-animal relationships, the moral consideration of animals and how nonhuman animals ought to be treated. The subject matter includes animal rights, animal welfare, animal law, speciesism, ani ...
* Animal cognition *
Animal welfare Animal welfare is the well-being of non-human animals. Formal standards of animal welfare vary between contexts, but are debated mostly by animal welfare groups, legislators, and academics. Animal welfare science uses measures such as longevity ...
* Animal welfare science *
Bridge locus In neuroscience the bridge locus for a particular sensory percept is a hypothetical set of neurons whose activity is the basis of that sensory percept. The term was introduced by D.N. Teller and E.Y. Pugh Jr. in 1983, and has been sparingly used. Ac ...
*
Animal consciousness Animal consciousness, or animal awareness, is the quality or state of self-awareness within a non-human animal, or of being aware of an external object or something within itself. In humans, consciousness has been defined as: sentience, aware ...
*
Cruelty to animals Cruelty to animals, also called animal abuse, animal neglect or animal cruelty, is the infliction by omission (neglect) or by commission by humans of suffering or harm upon non-human animals. More narrowly, it can be the causing of harm or suf ...
* Emotion in animals *
Ethics of uncertain sentience The ethics of uncertain sentience refers to questions surrounding the treatment of and moral obligations towards individuals whose sentience—the capacity to subjectively sense and feel—and resulting ability to experience pain is uncertain; ...
*
List of mutilatory procedures on animals Numerous procedures performed on domestic animals are usually more invasive than purely cosmetic alterations, but differ from types of veterinary surgery that are performed exclusively for urgent health reasons. Such procedures have been grouped ...
*
Psychology of eating meat The psychology of eating meat is a complex area of study illustrating the confluence of morality, emotions, cognition, and personality characteristics. Research into the psychological and cultural factors of meat-eating suggests correlations with ...
* Moral status of animals in the ancient world * Neural correlates of consciousness * Philosophy of mind * Three Rs (animal research) * Wild animal suffering


References


External links

* Animal Ethic
"Indicators of animal suffering"
''Animal Sentience''. * Kent, J. E. & Molony, V
''Guidelines on the Recognition and Assessment of Pain in Animals''
* Crawford, R
''A Reference Source for the Recognition & Alleviation of Pain & Distress in Animals''
United States Department of Agriculture.
Recognition and Assessment [of Pain
/nowiki>">f Pain">Recognition and Assessment Animal emotions">f Pain
/nowiki> Animal Welfare Information Center (USDA) {{ethology Pain in animals"> Animal emotions Cruelty to animals