Health & Management / Ruminants Pain Management / Techniques and protocols OVERVIEW:
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Introduction and General Information

Assessment of pain in animals, as in human infants that are unable to verbally describe their pain, is recognised to be difficult. (J4.221.w8, B323.3.w3)
  • In order for pain to be assessed it is necessary to consider various biochemical, physiological and behavioural parameters. No system is available whereby the relative importance of these different parameters may be compared effectively. (J3.118.w4)
  • The primary way in which pain in animals is assessed is by measurement of behavioural and physiological responses to procedures which are putatively painful. (J284.71.w1)
  • Assessment of pain is largely subjective and interpretation of the degree of pain will inevitably vary to some extent between individual observers. (P54.2.w9)
    • Observer experience is important for accurate assessment of pain. (P54.2.w16)
  • Note: Relatively little is known about assessment of chronic pain in animals. (P54.2.w15)
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Responses to Pain

It is possible to recognise several types of responses to pain: (J3.118.w4, J284.75.w1, B325.w4) 
  • Responses which are designed to modify the individual’s conscious behaviour, allowing it to learn and thereby avoid situations leading to pain. Responses of this type result from the aversive quality of pain and require high level central nervous system (CNS) function. (J3.118.w4, J284.75.w1, P61.62.w5)
  • Responses designed to protect the individual/part of the individual. These responses are often automatic and may range from withdrawal reflex to running away or attacking the source of the stimulus (e.g. by biting it). (J3.118.w4, J284.75.w1, P61.62.w5, B325.w4)
  • Responses designed to minimise pain, and in doing so improve healing. This includes reducing activity, for example lying down, standing very still or taking a different posture. (J3.118.w4, J284.75.w1, P61.62.w5, B325.w4)
  • Responses designed to convey the presence of the painful experience to other individuals, of the same or another species, which might assist in alleviating the situation, for example by eliciting assistance. (J3.118.w4, J284.75.w1, P61.62.w5; B325.w4)
    • Such responses include pain-specific vocalisations, postures and facial expressions, but may be suppressed under evolutionary pressure in order to avoid the attention of predators. (J3.118.w4, B325.w4)

These responses frequently occur concurrently. (B325.w4)

In response to pain, farm animals undergo changes in heart rate, blood pressure, temperature, activity level, body weight, food intake, behaviour, mental status, posture, facial expression, responses to handling and vocalisation, although there are variations in the recognizable signs of pain between species and between individuals. (J4.221.w4)

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Assessment - General and Background Information

General information about the animal and its background may be useful for interpretation. (J3.118.w4)

Details of the animal:

  • Species, breed, genetic strain, age, sex, weight, reproductive status and activity of the animal should be recorded. (J3.118.w4, B325.w5)
    • Younger animals may react differently to pain than older animals, for example being more responsive to pain but, due to lesser learning experiences, with less sensitivity to anxiety associated with anticipation of a procedure. (J3.118.w4, B325.w5)
  • The animal’s history including origin and previous experience should also be recorded, e.g. wild caught or captive bred, parent or hand-reared. (J3.118.w4, B325.w5)

History of the animal(s) and establishment:

This should include:

  • The signs and course of the present problem. (J3.118.w4, B325.w5)
  • Previous problems in the animal(s) under consideration or others in the same or similar environments; this includes medical and behavioural problems. (J3.118.w4, B325.w5)
  • Stocking density, the size of the group/colony, (J3.118.w4, B325.w5) also behavioural interactions within the group. (V.w5)
  • Access to other species including feral animals and potential disease vectors such as insects, rodents and birds. (J3.118.w4, B325.w5)
  • Intake of food and water, including the amount, type of food, pattern of feeding, food wastage and selection, growth and weight gain (or loss), size and weight for age. (J3.118.w4, B325.w5)
  • Environmental parameters: temperature, humidity, ventilation, availability of food and water, presence of any toxic, infectious or allergic contaminants. (J3.118.w4, B325.w5)
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Factors affecting Behaviour and Signs of Pain

Species/Breed/Strain:
  • The responses to pain may vary markedly between species. (B322.4.w4)
  • An understanding of the normal behaviour for the species is required in order to properly interpret behavioural signs of pain. (B322.4.w4)
  • Prey species are likely to show few overt signs of pain as this may attract the attention of predators. (J290.21.w1, J303.7.w1)
  • Social species are more likely to show signs of pain which may elicit help and support from other members of the group than are solitary or herd species. (J290.21.w1)
  • The responses to pain also may vary markedly between breeds or strains within a species. (B322.4.w4)

Ruminants:

  • Behavioural signs of pain in ruminants, which are prey species, are generally subtle, since overt signs would increase the risk of the individual being noticed and targeted by a predator. (J3.152.w1, J290.21.w1, J303.7.w1, J303.7.w2)

Individual variation:

  • Even within a particular breed or strain of animal there will be individual variations in behavioural responses to pain. (B322.4.w4)
    • Knowledge of the normal behaviour of the individual is required for correct interpretation of behavioural signs. The individual's temperament may affect, for example, whether it responds in an aggressive or a passive way to pain. (B322.4.w4)

Age:

  • Younger animals may react differently to pain than older animals, for example being more responsive to pain but, because of lesser learning experiences less likely to feel anxiety associated with anticipation of a procedure. (J3.118.w4, B325.w5)
  • It should be remembered that very young animals may have a limited repertoire of responses. (B322.4.w4)

Isolation:

  • Isolation acts as a stressor for herd animals, particularly herbivores, and signs of pain may not be shown overtly in such circumstances. (B322.4.w4)
  • Isolated neonates tend to be less likely to show overt signs of pain or to vocalise in response to pain. (B322.4.w4)

Presence of potential predators:

  • Prey species in particular will tend to mask signs of pain (and of illness in general), particularly in the presence of potential predators. (B322.4.w4, J16.36.w1)
    • e.g. for cats, dogs are recognised as predators. (B322.4.w4)
  • It is important to recognise that for wild and feral animals and even farm animals and laboratory animals humans are recognised as predators. This may be true also for pet animals in the presence of a human whom they do not know. (B322.4.w4)
  • Many zoo animals react to the veterinarian as a potential predator (V.w5)

Presence or absence of owner:

  • Demonstration of behavioural signs of pain, of pet animals, particularly dogs, may vary markedly depending on the presence or absence of the owner. (B322.4.w4)

Environmental location:

  • Animals which are not in their normal surroundings will tend to be nervous, apprehensive or excited, and this may mask signs of pain. (B322.4.w4)

Physical status, physical restraint, effects of drugs:

  • Animals may be physically unable to employ normal methods of reaction to pain due to injury or severe debility, physical restraint, or the effects of drugs, including sedatives. (J4.213.w2, W513.Jun04.w1, B322.4.w4)
    • An animal which has been given neuromuscular blocking drugs will be unable to react to pain by physical means, including vocalisation. (J3.118.w4)
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Behavioural Assessment of the Individual's Pain

Assessment of the general appearance and undisturbed behaviour of the animal should be carried out before it is approached; parameters such as respiratory rate and character should also be evaluated before the individual is approached. (J3.116.w3)

Behaviour is a valuable index of distress, and pain-related behaviours can be good indices of the duration and of the different phases of an experience, "however behavioural changes are often poorly correlated with the maximum intensity of the noxious experience as indicated by physiological variables." (J10.48.w4)

It is important to acknowledge that, in evolutionary terms, showing an abnormality (including abnormal behaviour in response to pain) may reduce the chance of survival (therefore behaviours indicating pain may not be shown); however it would be wrong to assume that because there is no visible evidence of pain there is no pain. That is, pain cannot always be detected by visual observation. (J4.221.w4)

Wild animals are very likely to hide signs of pain even when presenting with severe injuries. (J34.24.w2) 

  • NB. The normal behaviour of the species must be known and the assessing individual must have experience with the species in order for abnormal behaviour associated with pain to be assessed. (J3.116.w3, J4.213.w2, J15.24.w1, J147.12.w1, B323.3.w3, J288.59.w1, P54.2.w16, W513.Jun04.w1)
    • Behaviour may also be affected by the environment; it is necessary to know the normal behaviour of the particular type of animal within its particular environment, if abnormal behaviour associated with pain is to be properly assessed. (P61.62.w3)
    • Behavioural signs of pain in animals are often very subtle; recognition of these signs is probably best developed in those working closely with the animals. (J4.213.w2, J290.21.w1, W513.Jun04.w1)
    • Behavioural responses to the same insult may vary between species: in calves abnormal standing and foot stamping may be good indicators of pain following castration, while abnormal lying postures and restlessness may be better indicators in lambs. (J21.56.w1)
  • Most species of mammals show escape behaviour, sometimes with aggression, and vocalisation, in response to acute pain. (B322.4.w4); immobility may also be seen. (P49.1.w2)
  • Animals experiencing pain often display a striking absence of normal behaviour. (B325.w6)
  • Assessment of pain may be improved by combined use of two or more indices rather than just one indicator; statistical (multivariate) analysis may be used to indicate appropriate combinations of indices. (J284.75.w1)
    • For example a combination of the time spent lying in an abnormal ventral position and the time spent in abnormal active behaviours was shown to give a more accurate indicator of acute pain following castration and tail docking in lambs than any one behavioural or physiological indicator. (J284.75.w1)

Mental status:

  • Assessment of the mental status should be made in relation to the normal behaviour of the individual animal and of individuals of its species/breed/strain. (J3.118.w4, B325.w5)
    • This may often be best assessed by a person with personal knowledge of that animal in health – the stockperson, keeper or attendant. (J3.118.w4, B325.w5)
    • Descriptive terms which may be used to describe mental state include: dull, depressed, unresponsive, unaware, apprehensive, anxious, bright, alert, aware, excitable, hypersensitive, aggressive, or timid. (J3.118.w4, B325.w5)
  • Assessment should take into account the animal’s interaction with other individuals of the same species and, if applicable, any changes in its ability to perform previously learned tasks or respond to previously learned commands. (J3.118.w4, B325.w5)
  • There may be changes in the animal's personality in response to pain, such as aggression in a normally docile animal, or a normally aggressive individual becoming quiet and docile. (J4.213.w2, W513.Jun04.w1)
  • Individuals in pain may appear generally unresponsive and withdrawn, and not react to a person in their normal manner. (J4.213.w2, W513.Jun04.w1)
    • Responses to standard stimuli, such as the approach of the stockperson, should be assessed. (J284.75.w1)
  • The state of consciousness or awareness may be assessed by use of appropriate tests such as response to visual or auditory threats or enticements (allowing for the fact that such responses depend on the presence of the motor competence to respond to the tests: use of neuromuscular blocking agents abolishes such responses, without affecting the state of consciousness). (J3.118.w4, B325.w5)
  • The overall state of the CNS may be assessed by responses to reflex and flexor withdrawal reflex, to determine whether, and to what degree, CNS function is depressed. (J3.118.w4, B325.w5)

In cattle: 

  • An individual in pain may appear dull, depressed, and show little interest in its surroundings. (J3.118.w4, J303.7.w2)
  • Responses of cattle to abdominal or thoracic visceral pain include general dullness and depression. (B322.4.w4, P54.2.w9)

In sheep: 

  • There may be no overt signs of pain. (B325.w6)
  • An individual in pain may appear dull, depressed, and show little interest in its surroundings. (J3.118.w4, J4.221.w4, P54.2.w9)
  • Dullness with chronic pain. (B322.4.w4)
  • The response to the approach of the shepherd or sheepdog should be assessed. (J284.75.w1)
  • A sheep in pain may stand away from the rest of the flock. (J4.221.w4)

In goats:

  • An individual in pain may appear dull, depressed, and show little interest in its surroundings. (J3.118.w4)

Abnormal activity:

  • This includes a reduction in or absence of normal behaviours. (B325.w6)
  • Behaviours shown by an individual which are unusual, or which are not being shown by other animals in its group, may suggest pain. (P61.62.w3)
  • Abnormal activity may be generalised and range from total inactivity (lethargy and recumbency) to restlessness (pacing, repeated lying down and getting up again) or manic hyperactivity. (J3.118.w4, J4.213.w2, B325.w5, W513.Jun04.w1)
    • The type and extent of abnormal activity will depend on factors including the species, the severity of the pain and the location of the pain. It is most likely to be recognised by the person (stockperson, keeper or attendant) who normally cares for the animal. (J3.118.w4, B325.w5)
  • Pain may affect wake/sleeping patterns. (B325.w5; J297.22.w1)
  • Pain may affect exploratory behaviour. (B325.w5)
  • Eating and foraging behaviour may be changed. (B325.w5; J297.22.w1)
  • Normal grooming behaviour may be changed. (J297.22.w1)
  • Specific abnormal activities may result from pain in particular anatomical locations, for example quidding /cud-dropping due to pain in the mouth/teeth in horses and cattle and kicking at the abdomen in response to abdominal pain in horses (and to a lesser extent in cattle). (J3.118.w4, B325.w5)
  • Pacing, repeated lying down and getting up, rolling and thrashing, looking and/or kicking at the abdomen are all signs of acute pain. (J288.59.w2)
  • Licking, biting and scratching may be directed at a painful area, and the painful part of the body may be shaken. (J4.213.w2, W513.Jun04.w1)
  • Persistent severe pain may produce significant changes in normal behaviours. (J297.22.w1)

In ruminants:

  • Impaired function of the rumen may occur in response to any painful condition. (J3.113.w)

In cattle:

  • Inappetance and weight loss may occur, also in milking cows a sudden reduction in milk yield (milk-drop). (J3.118.w4, B325.w6, P54.2.w9)
  • Kicking at the abdomen may occur in response to abdominal pain but is generally less marked than in horses. (J3.118.w4, B325.w6)
  • Flank kicking may be seen with severe visceral pain. (B322.4.w4)
  • Grooming commonly ceases, due to unwillingness to relax a rigid posture to turn the neck. (B325.w6, P54.2.w9)
  • Frequent lying and standing, or prolonged recumbency, may be seen in cattle with severe visceral pain. (B322.4.w4)
  • Straining is indicative of pain associated with the genital or urinary tracts (either obstruction or inflammation). (B322.4.w4)
  • Persistent licking at or kicking at a particular area may occur in response to localised pain in that area. (B325.w6)
  • Lame cows may move about less. (J3.133.w2)
  • Cattle in pain may be reluctant to move. (J4.221.w4)
  • Straining may be seen with pain of the urogenital tract. (B322.4.w4)

In goats:

  • Grooming commonly ceases. (B322.4.w4)
  • With visceral pain cessation of cudding, inappetance, flank watching and flank kicking. (B322.4.w4)
  • Goats in pain may appear agitated and show foot stamping behaviour. (J4.221.w4)
  • There may be an absence of normal head pushing behaviour. (B325.w6)

In sheep:

  • Tooth grinding and head pressing are seen associated with severe pain. (B322.4.w4)
  • With visceral pain, tooth grinding, lip curling and cessation of cudding may occur. (B322.4.w4)
  • In lambs, various abnormal activities may be seen following castration and tail docking.
    • Repeated lying down and standing up may be noted. (B325.w6, J21.55.w1)
    • Abnormal activities, rarely seen in unstressed individuals, include curling of the upper lip, rolling briefly onto the back, restlessness, immobility, extension of the neck and hyperventilation. (J21.51.w1)
    • There may be tail wagging, neck extension, curling of the dorsal lip, kicking and rolling. (B325.w6, J21.51.w1)
    • Restlessness, kicking, stamping, rolling, jumping, easing of the hind quarters, licking/biting at the affected site and tail wagging are all recognised. (J21.55.w1, J284.75.w1)
    • Prolonged periods of inert lateral lying may be seen, during which it can be difficult to elicit evidence of conscious awareness; the ewe sometimes paws vigorously at its lamb in response to this state. (J284.75.w1)
    • "Statue standing", seen after surgical castration and tail docking in particular, in which the lamb remains immobile for several minutes at a time. This may minimise stimulation of sensitized tissues. (J21.55.w1)

Posture:

  • In some species postural mechanisms are utilised for communication of experiences. (J3.118.w4, B325.w5)
  • A "tucked up" appearance due to tensed abdominal and back muscles is particularly noticeable in some species including dogs, cats, and rodents. (J4.213.w2, W513.Jun04.w1)
  • Postural changes are commonly elicited by painful foci in particular anatomical locations: dogs with pharyngeal pain will often stand with the head and neck extended, those with abdominal pain may lie with the belly on a cold floor, while hens with abdominal pain may adopt a “penguin like” stance. Horses with pain in one forefoot may “point” the toe. (J3.118.w4, B325.w5)
  • Changes in posture can be voluntary or involuntary. (J284.75.w1)
    • Involuntary: nociceptor activity can elicit involuntary spinal and brainstem reflexes; some of these may cause hyper-reflexia including an increase in muscle tone. (J284.75.w1); for example following lamb castration using a rubber ring, full hind limb extension may be seen. (J284.75.w1)
    • Voluntary: an immobile stance may be adopted to reduce/avoid stimulation of hyperalgesic tissues, for example following castration. (J284.75.w1)

In cattle:

  • Abdominal splinting may be seen in response to visceral pain. (B322.4.w4)
  • Individuals with rigid posture due to pain may show signs of a lack of grooming, due to reluctance to turn the neck. (J3.118.w4)
  • Individuals with pain due to acute abdominal conditions (e.g. intestinal strangulation) adopt a characteristic stance with one hind foot directly in front of the other. (B325.w6)
  • With traumatic reticuloperitonitis a slightly arched back and stretched out head and neck is characteristic. (P54.2.w9)
  • With intussusception the back may be depressed and flexed to one side. (P54.2.w9)
  • Lame cows may adopt abnormal postures including abnormal lying and sitting postures, such as lying with the hindlimbs stretched out as well as abnormal standing postures. (J3.133.w2)
    • Abnormal standing postures in lame cows include the back being arched (common). Lame cows in cubicles may stand with only the front feet in the cubicle, or with one hind foot in the cubicle and the other in the passage. The lame foot may be held stretched forward (under the body for a hind foot) or with only the toe tips touching the ground. If lame on both hind feet then frequent shifting of the weight on the hindfeet may occur. (J3.133.w2)
    • Cows with moderate lameness show arching of the back when standing. (J72.54.w1, J296.47.w1)
    • In individuals with fractures of the inner pedal bone of both front feet a pronounced cross-legged stance is seen. (P54.2.w9)
  • Arching of the spine commonly indicates lameness. (J15.24.w2)
  • Severely lame individuals may show extreme reluctance to bear any weight on the affected limb or may be non weight bearing on that limb. (J296.47.w1)
  • Lame individuals may show repeated lifting of the affected limb or limbs while stationary. (J303.7.w2)
  • Lame individuals may attempt to support their weight on the least painful part of the claw. (J303.7.w2)

In sheep:

  • Changes in posture and movement may be noted. (J3.118.w4, B325.w6)
  • Abnormal standing postures and abnormal lying postures are commonly seen in lambs following castration and tail docking and include:(J21.55.w1, J284.75.w1)
    • The lamb may repeatedly lie down and stand up; (B325.w6)
    • Following lamb castration using rubber rings, full hind limb extension may be seen (involuntary reflex).;(J284.75.w1)
    • Ventral lying with partial extension of one leg; (J284.75.w1)
    • Ventral lying with full extension if one or more legs; (J21.55.w1, J284.75.w1)
    • Lateral lying with a shoulder down and the head up; (J21.55.w1, J284.75.w1)
    • Abnormal stance or detectable swaying; (J284.75.w1)
    • Immobile/statue standing; (J284.75.w1)
    • Standing still with the hind legs stretched back; (J21.55.w1)
    • Standing with the back hunched; (J21.55.w1)
    • Standing and trembling. (J21.55.w1)
  • Note: Statue" standing is seen more following surgical castration than following rubber ring or combined rubber ring and Burdizzo clamp castration. (J21.55.w1)

In goats:

  • Changes in posture and movement may be noted. (J3.118.w4, B325.w6, J4.221.w4)

Gait/Locomotor signs:

  • Lameness is a common manifestation of limb pain. (B322.4.w4)
    • Lameness and/or non-use of an extremity may be seen. (J288.59.w2)
    • The affected limb may be carried. (J4.213.w2, W513.Jun04.w1)
  • Reluctance to move may be seen. (J4.213.w2, W513.Jun04.w1, J288.59.w2)
  • Note: bilateral limb pain may not cause overt lameness. (B322.4.w4)
  • The gait will be modified by pain associated with locomotion and may affect a single limb, only the hindlimbs, only the forelimbs, or all four limbs. (B325.w5)
  • It is possible to grade lameness using a scoring system. (B325.w5, J15.24.w2, J296.47.w1, J303.7.w2)
  • It is important to rule out mechanical and other non-painful causes of lameness before ascribing this sign to pain; this is often achievable by using local, regional or general analgesic or anti-inflammatory treatment to reduce painful signs. (J3.118.w4)

In cattle:

  • Adduction or abduction of the limb may be seen, reducing the amount of weight borne on a painful digit. (P54.2.w9)
  • Lesions affecting both hind legs or feet may lead to a stilted gait and arching of the back as weight is transferred to the forelimbs. (B322.4.w4)
    • There may be weight loss due to reluctance to move reducing the ability to compete with other individuals for access to feed. (B322.4.w4)
  • Cows with even mild lameness, without obvious gait change, may show arching of the back when walking; this is a sensitive indicator of lameness, particularly when tenderness of the feet is bilateral. (J72.54.w1, J296.47.w1)
  • As lameness increases the affected individual may show short-striding of one or more limbs, then the gait becomes one deliberate step at a time, with one or more limbs being favoured, until in severe lameness there is an extreme reluctance or inability to bear weight on one or more limbs/feet. (296.47.w1)
  • Cattle may be reluctant to move. (J4.221.w4)
    • Reluctance to move may be seen with conditions such as traumatic reticuloperitonitis, laminitis and generalised peritonitis. (P54.2.w9)
  • Non-weight bearing may be seen on the affected limb. (P54.2.w9)

In sheep:

  • General reluctance to move. (B325.w6)
  • Individuals with severe foot rot commonly graze standing on their knees to reduce pain associated with weight-bearing. (B322.4.w4)
  • In lambs following castration/tail docking, recognised abnormal locomotion includes abnormal and unsteady gait, ataxia, swaying, stilted walking, walking backwards, walking on the knees and falling over. (J21.55.w1, J284.75.w1)

In goats:

  • General reluctance to move. (B325.w6)

Facial expression:

  • This is an important means of communication in some species although subtleties of facial expression have not been analyses for most species. (J3.118.w4, B325.w5)
  • Persons working with particular species frequently become aware of facial expressions although they may be unable to describe them in detail. (J3.118.w4, B325.w5)
  • Dull eyes, dilated pupils, pinning back of the ears, grimacing and a sleepy expression are examples of changes in facial expression which may be seen in animals experiencing pain. (J4.213.w2, W513.Jun04.w1)

In cattle:

  • Changes in facial expression may be seen associated with pain. (J4.221.w4)

In sheep and goats:

  • Facial expression changes may be seen associated with pain. (J3.118.w4, J4.221.w4, B325.w6)

Vocalisation:

  • Vocalisation is a very common unlearned reaction to pain (J297.22.w1)
  • Vocalisation in response to pain may be voluntary or involuntary and may be “angry” or “plaintive”. (J3.118.w4, B325.w5)
  • Vocalisations in large animals may include grunts, bleats and crying; tooth-grinding may also occur. (J288.59.w2)
  • In some cases there may be characteristic noises associated with a particular act or physiological function, such as a dog with a painful bladder yelping when urinating. If pain is longer than momentary then associated vocalisations are generally repeated. (J3.118.w4, B325.w5)

In cattle:

  • Grunting. (J3.118.w4, B325.w6, J4.221.w4)
    • Grunting may be heard with gastrointestinal pain, including traumatic reticuloperitonitis, but also with respiratory pain due to pleurisy and bronchopneumonia. (P54.2.w9)
  • Tooth grinding. (J3.118.w4, B325.w6, J4.221.w4, W513.Jun04.w1)
    • Tooth grinding is a common response to abdominal pain. (P54.2.w9)
  • Bellowing. (B322.4.w4, B325.w6, J4.221.w4)
    • Cattle rarely cry out in response to pain. (P54.2.w9)

In sheep:

  • Sheep rarely grunt or vocalise. (B322.4.w4)
  • Individuals may grunt. (J3.118.w4)
  • Teeth grinding is common in individuals experiencing pain. (J3.118.w4, J4.213.w2, J4.221.w4W513.Jun04.w1); particularly with severe or visceral pain. (B322.4.w4)
    • Tooth grinding may occur for example with urethral obstruction by calculi. (P54.2.w9)
  • Bleating may occur. (J4.221.w4)
    • Sheep sometimes bleat in response to pain, but less often than do goats. (P54.2.w9)

In goats:

  • Goats tend to vocalise more in response to pain than do cattle or sheep. (J3.118.w4, P54.2.w9)
  • Vocalisation and tooth grinding may both occur in response to pain. (J4.221.w4, B325.w6)
    • A marked increase in bleating and crying is common. (B322.4.w4)
    • Tooth grinding is common in individuals experiencing pain. (J4.213.w2, W513.Jun04.w1)
      • Tooth grinding may occur for example with urethral obstruction by calculi. (P54.2.w9)

Response to handling:

  • Individuals in pain may show changes in their normal responses to handling and to being manipulated. (J3.118.w4, B325.w6)
    • This may be include either aggression towards the examiner or avoidance and withdrawal behaviour. (J288.59.w2)
  • Palpation may produce changes in posture, vocalisation or attack; this may reveal pain which was not overtly observable beforehand. (J3.118.w4, B325.w5)

In cattle: 

  • Rigidity of posture (designed to immobilise the painful area) may be seen, or a violent response to handling may be noted. (J3.118.w4, B325.w6, P54.2.w9)
  • Kicking may occur in response to handling of a crushed teat. (P54.2.w9)
  • With mastitis there may be obvious resentment of any handling of the affected mammary gland, due to allodynia. (B322.4.w4)
  • The foot may be snatched away if a painful digit is manipulated. (P54.2.w9)
  • Abdominal guarding is evident on ballotment in individuals with generalised peritonitis. (P54.2.w9)

In goats:

  • Resentment of handling is a common sign of pain. (B322.4.w4)
Change in appetite:
  • Reduced appetite and water intake may be apparent; this may lead to weight loss and dehydration. (J4.213.w2, W513.Jun04.w1)

Clinical examination:

  • The animal should be examined for the presence of any disease due to infectious, toxic or allergic agents, dietary deficiencies or abnormalities, or trauma. (J3.118.w4)
  • It should be noted that the presence of pre-existing disease may mask the presence of pain. (J3.118.w4)
  • Physiological signs of pain including increased heart rate, increased respiratory rate and raised body (rectal) temperature may be noted. (J3.118.w4, B325.w5, J4.213.w2, W513.Jun04.w1) SEE SECTION BELOW: Physiological Evidence of Pain

In cattle:

  • Signs of reduced grooming may be noted with chronic pain (both somatic and low grade visceral). (B322.4.w4)
  • Lachrymation and blepharospasm indicate ocular pain. (B322.4.w4)

In sheep:

  • Individuals with severe foot-rot tend to lose body condition. (B322.4.w4)
  • Loss of condition is seen with chronic pain. (B322.4.w4)

In goats:

  • May be signs of decreased grooming. (B322.4.w4)

Signs of chronic pain:

Individuals in chronic pain may show changes in feeding, social, sleeping and explorative behaviour, guarding behaviour, with avoidance of situations which aggravate the pain and seeking of factors/environments which relieve the pain, self-care of a painful area of the body, self-mutilation, signs of stress and decreased productivity. (P49.1.w2)

Behavioural indicators of chronic pain may be vague and subtle. (J4.221.w6) These may include:

  • Loss of appetite;
  • Changes in personality;
  • Alterations in urinary and defecatory activity;
  • Soiling due to reduced or absent grooming.
(J288.59.w2)

Persistent severe pain may produce significant changes in normal behaviours such as feeding and drinking, the sleep/wake cycle, grooming and sexual behaviours. (J297.22.w1)

In cattle:
  • Loss of weight and condition may be seen in lame individuals. (J3.132.w4)
  • Reduced grooming. (B322.4.w4)

In sheep:

  • Loss of weight and condition may be seen in lame individuals. (B322.4.w4, J15.26.w1)
  • General dullness. (B322.4.w4)

Systems to assess the severity of pain:

Assessment of the severity of pain may employ a Numerical Rating scale (NRS) or a Visual Analog Scale (VAS).

  • A Numerical Rating scale (NRS) is a scale used for the subjective measurement of a clinical sign/syndrome, in which numerical scores are given (e.g. 0 to 4). A description is given for each score. The observer chooses, for each individual observed, the number on the scale which they consider most closely matches that individual. (J13.54.w5; D152.w4)
    • This system groups information in discrete units, which may place a constraint on the observer. (J13.54.w5)
    • The NRS can also be used without a descriptor for each score, but is improved by the addition of the descriptions. (D152.w4)
  • The Visual Analog Scale (VAS) is a scale used for subjective measurement of clinical signs/syndromes, including pain. It uses a straight line, usually 100 mm long, with the limits of the line marked with perpendicular lines. The two ends of the line are labelled with verbal descriptions indicating the lower and upper extremes of the clinical sign/syndrome which is to be evaluated (to make it easier for the observer to assign intermediate points), and the observer marks the line at a position representing the severity of that sign/syndrome. A score of 0 to 100 mm is awarded based on the measurement of the distance (in mm) along the line where the observer's mark has been made. In humans, self-scoring of pain is sometimes carried out using a VAS. (J13.54.w5, D152.w4)
    • For assessment of lameness, the ends of the line may be marked with, for example, "sound" and "could not be more lame." (J13.54.w5)
    • For self-assessment in humans the scale is marked "No pain" at one end and "excruciating or unbearable pain" or "worst pain imaginable" at the other. (J290.21.w2; J297.22.w1)
    • The VAS allows a continuous assessment of pain (rather than the discrete measurements in an NRS). (D152.w4)
  • While verbal descriptors - mild, moderate, severe, excruciating, burning, sharp, dull, localised etc. are used by humans to describe pain they are feeling, it has been found difficult to use these effectively to describe pain being felt by animals. (D152.w4)
  • Examples of systems used to classify lameness in cattle and sheep are given in the section below: Lameness Classification Systems.

Assessment of pain in experimental situations:

There are several difficulties which arise when comparing the relative degrees of pain and distress experienced by animals undergoing, for example, different methods of castration or other management procedures which may be painful. 

"A suite of behaviours indicative of pain may be used to determine the duration of the noxious experience, but the use of a single behaviour may be misleading." (J10.47.w3)

In studies of procedures ("treatments") which are likely to be painful:

  • "A behaviour is likely to be a useful indicator of noxious sensory input leading to pain and distress if it is not seen in control animals but is seen after treatment in treated animals." (J10.47.w3)
  • "Behaviour elicited by treatment can be validated as measures of noxious sensory input if effective local anaesthesia returns levels close to those seen in control animals." (J10.47.w3)
  • "Unique behaviours elicited by different treatments cannot be used meaningfully to compare the pain or distress responses to these treatments; behavioural responses common to both treatments are required for each comparison." (J10.47.w3)
  • "When different treatments elicit unique behavioural responses this probably occurs because the sensations experienced by the animals will not be the same, if different tissues are damaged or the same tissues damaged in different ways. Thus surgical castration causes apparent reluctance to move, whereas ring castration causes restlessness." (J10.47.w3)
  • "Comparison should only be made between similar animals (age, sex, genotype, management) under similar conditions." (J10.47.w3)
    • However some studies have used animals of varied genotypes (J21.66.w1) while others have been carried out specifically to compare responses to a given procedure between animals of different ages. (J21.55.w1)

In castration of lambs, restlessness and lateral lying appear to be indicative of ischaemic pain. (J10.47.w3)

Problems associated with behavioural observations include variations between individuals in behaviours displayed, the limited number of behaviours recorded and the presence of false-positive behaviours (i.e. behaviours which are considered to indicate pain) in control animals. (J21.66.w1)

  • Visual Analog Scale (VAS) scoring for active behaviours, unresponsive behaviour and scrotal pain (on palpation) has been used in association with cortisol measurements and mechanical nociceptive threshold testing for quantification of pain responses associated with castration. It was noted that active behaviours were more apparent following ring castration while unresponsive behaviours were more apparent following surgical castration, thus that use of either behaviour type alone for pain scoring would be misleading in pain assessment. While cortisol responses were higher in ring castrated and surgically castrated lambs than in those castrated by combined ring plus Burdizzo clamp (full scrotal width), the prolonged period of hypoalgesia (measured by raised mechanical nociceptive threshold) seen with the combined method (and with surgically castrated lambs) but not with ring castrated lambs, and abolition of the hypoalgesia if local or general anaesthesia was given, indicated that application of the clamp was itself painful and that this is responsible for the rise in nociceptive thresholds and the active pain behaviours. (J21.66.w1)
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Lameness Classification Systems

IN CATTLE:

Various systems have been developed to score lameness of individual cows, including the following: 
Scoring system Score/grade Observations Comments
Manson & Leaver, 1988 (J301.47.w1) 1.0 "Minimal abduction/adduction, no uneveness of gait, no tenderness" "Researchers commonly use this scoring system. It has nine points which can make it complicated to use. As nearly half of the scores in this system are dedicated to changes in gait prior to clinical lameness, it is useful for identifying early signs of discomfort. It takes considerable practice to learn this system and not all definitions are suited to animals already standing and walking. If possible, learn the system from someone who has used this scoring method before." (J15.24.w2)
1.5 "Slight abduction/adduction, no uneveness or tenderness"
2.0 "Abduction/adduction present, uneven gait, perhaps tender"
2.5 "Abduction/adduction present, uneven gait, tenderness of feet"
3.0 "Slight lameness, not affecting behaviour"
3.5 "Obvious lameness, some difficulty in turning, not affecting behaviour pattern"
4.0 "Obvious lameness, difficulty in turning, behaviour pattern affected"
4.5 "Some difficulty in rising, difficulty in walking, behaviour pattern affected"
5.0 "Extreme difficulty in rising, difficulty in walking, adverse effects on behaviour"
Tranter & Morris, 1991 (J10.39.w1) 0 "No abnormality of gait" In scoring lameness the following were noted: "the degree of difficulty in deciding which leg was affected; the degree and timing of head movement (the head usually moves up as the affected limb contacts the ground); the degree of sinking of the hind quarter on the sound side; any abduction or adduction of the limbs; shortening or lengthening of the stride (the hind foot is normally placed in exactly the same place as the front foot)." (J10.39.w1)

"A more simple scoring system with some useful guidelines for identifying lame cows. Wells and others (1993) produced a similar scale with the top score defined as "non-ambulatory". (J15.24.w2)

1 "lameness hardly noticeable"
2 "slightly lame"
3 "markedly lame"
4 "affected limb not weight bearing"
Wells et al., 1993 (J4.202.w1) 0 no gait abnormality: "gait abnormality not visible at a walk; not reluctant to walk" It was noted that although cows scoring "1" were not classified as clinically lame in this study, "cows with early or resolving lameness of clinical importance, however, undoubtedly also were included in this category." (J4.202.w1)
1 mild gait abnormality: "mild variation from normal gait at walk; includes intermittent mild gait asymmetry or mild bilateral or quadrilateral restriction in free movement"
2 moderate gait abnormality: "moderate and consistent gait asymmetry or symmetric gait abnormality, but able to walk without continuous stimulation"
3 severe gait abnormality: "marked gait asymmetry or severe symmetrical abnormality"
4 nonambulatory: "recumbent"
Whay et al., 1997 (J35.154.w2) 1 Sound "This system was designed to be used quickly without complicated and restricting descriptions. It includes a score for cows walking abnormally but which are not apparently lame or which potentially have multilimb lameness." (J15.24.w2)

 

2 Imperfect locomotion
3 Mild lameness 
4 Moderate lameness
5 Severe lameness
6 As lame as possible while upright
Sprecher et al., 1997 (J296.42.w1) 1 - Normal "The cow stands and walks with a level-back posture. Her gait is normal." "This system introduced the idea of looking at the cow's spine when trying to identify lameness." (J15.24.w2)

"The descriptors are somewhat confusing." (J303.7.w2)

2 - Mildly Lame "The cow stands with a level-back posture but develops an arched-back posture while walking. Her gait remains normal."
3 - Moderately Lame "An arched-back posture is evident both while standing and walking. Her gait is affected and is best described as short-striding with one or more limbs."
4 - Lame "An arched back posture is always evident and gait is best described as one deliberate step at a time. The cow favours one or more limbs/feet."
5 - Severely Lame "The cow additionally demonstrates an inability or extreme reluctance to bear weight on one or more of her limbs/feet."
Simple yes/no

Whay, 2002 (J15.24.w2)

No "Not lame"  "A very simple system will still give useful information about the prevalence of lame cows or animals. This type of simple scale is adequate for farm assurance assessments and allows identification of cows with tender feet or multilimb lameness." (J15.24.w2)
? "Not walking easily/not obviously lame/perhaps tender/showing discomfort when walking/perhaps lame on more than one limb" 
Yes "Lame" 
Whay et al., 2002 (P57.12.w2)

 

0 "Sound" "Overall prevalence of clinical lameness was defined as the sum of those animals scoring 2 and 3." (P57.12.w2)
1 "abnormal locomotion / tender footed"
2 "lame"
3 "severe lameness"
Whay et al., unpublished (see J303.7.w2) Visual Analog Scale (VAS) Line with the left end marked "completely sound" and the right end "could not be more lame" "This system gives greatest sensitivity of scoring with a representative mark/score placed somewhere between the defined ends of the 100 mm line. This is better done by the same person." (J303.7.w2)
Posture scoring system, O'Callaghan et al., 2003 (J147.12.w1) 1 Good/normal This system was based on the following description for sound (non-lame) cattle: "A sound cow walks with a level spine. The hind feet almost exactly trace the placement of the forefeet. The gait appears comfortable and the cow walks at an even pace. Feet point in the direction of travel." The scoring system was designed to assess deviations from this. Scores were given for each of the following individual indicators: spine curvature (the degree of spinal arching), speed (ease/comfort of gait), tracking (of hind feet onto fore feet positions), head carriage (extent of movement and level of head carriage) and abduction/adduction (rotation of the feet from the direction of travel, plus an overall locomotion assessment. (J147.12.w1)
2 Imperfect
3 Mildly abnormal
4 Moderately abnormal
5 Severely abnormal

IN SHEEP:

Systems used for scoring lameness in individual sheep include the following:
Scoring system (Reference) Score/grade Observations Comments
Ley et al. 1994, 1995 (J21.57.w1, J3.137.w6) 0 Normal movement Used together with scores for pathology of the feet. (J3.137.w6)
1 Occasional limping
2 Lifting foot while standing, use on movement
3 Carrying foot, but lame on movement
4 Carrying foot all the time
Welsh et al., 1993 (J13.54.w5) 0 "Clinically sound" "The VAS and the NRS are reproducible and repeatable methods of scoring lameness in sheep, but should not be used interchangeably." (J13.54.w5)

Comparing the NRS with the VRS (see below) it was noted that "the maximal NRS score of 4 was associated with VAS values > 68 mm, indicating that the NRS divisions did not reflect equal increases in lameness." (J13.54.w5)

The NRS (and the VAS) gives highly reproducible scores for a given observer; scores are more variable for sheep which are "moderately lame" than for those with either mild or severe lameness. (J13.54.w5)

1 "Barely detectable lameness"
2 "Obvious lameness"
3 "Severe head nod and possibly resting the affected foot when standing"
4 "Carrying foot at the trot"
Welsh et al., 1993 (J13.54.w5) Visual Analog Scale (VAS) Line with the left end marked "sound" and the right end "could not be more lame". (J13.54.w5) "This system gives greatest sensitivity of scoring with a representative mark/score placed somewhere between the defined ends of the 100 mm line. This is better done by the same person." (J303.7.w2)

The VAS (and the NRS) gives highly reproducible scores for a given observer; scores are more variable for sheep which are "moderately lame" than for those with either mild or severe lameness. (J13.54.w5)

"Visual analogue scales provide a continuous method of subjective method and remove the constraints placed on observers by the NRS, which groups information in discrete units." (J13.54.w5)

The VAS may allow more accurate interpretation "because it does not force observers to group unlike data." (J13.54.w5)

 

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Assessment of the Anatomical Location of Pain in Animals

"The source, location, and intensity of pain may not be readily identifiable." (J4.221.w4)

While some signs of pain are general, others are more specifically related to the location of the pain.

  • Licking, biting and scratching may be directed at a painful area, and the painful part of the body may be shaken. (J4.213.w2, W513.Jun04.w1) Cattle may kick at a painful area or persistently lick at a painful area. (B325.w6)

Foot and Limb Pain:

  • The posture of cattle may indicate the site of lameness: (J3.72.w3)
    • Frequent shifting of the weight from one foot to another is indicative of bilateral lameness; (J3.72.w3)
    • Abduction of the leg so that weight is borne mainly by the inner claw suggests the painful condition is affecting the outer claw; (J3.72.w3)
    • Standing with just the toes of the hind feet on the edge of the stall, so that no weight is on the heels, suggests pain in the heels. (J3.72.w3)
    • A cross-legged stance, with the affected foot or feet held well under the cow (adducted) transfers weight onto the outer claw and may be seen when the inner claw is the site of pain. (J15.14.w4)

Oral Pain:

  • Quidding (cud dropping) is a feature of pain of the mouth or teeth in ruminants. (B325.w5)

Ocular Pain:

Visceral Pain:

In cattle: 

  • Inappetance (total or partial), dullness, depression, increased respiratory rate, abdominal splinting, grunting. (B322.4.w4)
  • With severe pain bellowing, tooth grinding, cessation of rumination and cessation of cudding. (B322.4.w4)
  • Tachycardia, other sympathetic-mediated changes. (B322.4.w4)
  • With severe pain reluctance to move, flank kicking. (B322.4.w4)
  • Recumbency or repeated lying and standing. (B322.4.w4)
  • Separation from the herd with prolonged pain. (B322.4.w4)
  • Downward arching of the back together with treading of the hind feet with acute visceral pain. (B207.5.w5)
  • Adult cattle may lie down with abdominal pain, but rarely roll (unlike horses). (B207.5.w5)
  • With subacute pain the back is arched and the animal grunts on walking, on lying down, and on deep palpation of the abdomen. (B207.5.w5)
  • Immobility may be noted with subacute visceral pain. (B207.5.w5)
  • Calves may lie down and bellow with severe abdominal pain.(B207.5.w5)
  • Pain associated with traumatic reticuloperitonitis: 
    • A cow will often stop grooming due to reluctance to flex her neck and back. (P54.2.w9)
      • Return of lick marks following treatment is a good indicator that the pain has been removed. (P54.2.w9)
    • A marked inappetance may be seen, together with reduced frequency and amplitude of rumen contractions and decreased defecation. (P54.2.w9)
    • A marked reduction in milk yield may be noted. (P54.2.w9)
    • Grunting occurring when the animal walks (particularly downhill), defecates or urinates. (P54.2.w9)
    • Grunting in response to upward pressure behind the xiphisternum. (P54.2.w9)
    • Grunting when the withers are pinched, stimulating the cow to crouch suddenly and stretch the abdominal floor. (P54.2.w9)
  • Pain associated with intestinal obstruction: Acute abdominal pain is indicated by the animal kicking at its abdomen, uneasy treading with the hind legs, depression of the back and sometimes groaning or even bellowing with pain. (B207.6.w6)

Pain associated with the Urinary or Genital Tract:

  • Straining is an obvious sign of pain of either the genital or urinary tract. (B322.4.w4)

Elicitation of pain by examination:

Pain may be elicited as part of clinical examination and is an essential part of the examination. (B207.2.w2)

  • Techniques to elicit pain include:
    • Pressure by palpation, including firm ballotment with a fist and use of a pole beneath a cow to arch the back upwards. (B207.2.w2)
    • Pressure by compression, for example of parts of the hoof to detect the location of the painful area. (B207.2.w2)
    • Active movement (e.g. by making the animal walk). (B207.2.w2)
    • Passive movement to flex and extend parts of the body such as limbs and neck. (B207.2.w2)
    • Eliciting the cough reflex to stimulate pain associated with coughing. (B207.2.w2)

Pain associated with foot lesions:

  • Pain together with heat and swelling are the classical signs of foot lesions causing acute lameness. (B359.14.w14)
  • In sheep with a white line lesion, the affected digit should be identifiable by the pain response on examination, as well as by the heat of the digit. (B346.w4)
  • A coronary band that is painful, swollen and hot indicates infection which has tracked into deeper structures of the foot such as the navicular bursa or tendon sheaths. (B344.31.w31)
  • Localised pain may be evident, for example pain on handling of the coronary band of the affected digit in sheep with septic pedal arthritis. (J15.17.w3)

Pain associated with infected joints:

  • Pain and swelling may be noted at the affected joints. (B344.32.w32)
    • Note: in calves lameness due to joint infection may be apparent before the joint swelling and pain on examination of the affected joint(s). (B344.32.w32)

In cattle with abdominal pain:

  • With acute localised pain (e.g. associated with traumatic reticuloperitonitis), while listening over the trachea with a stethoscope, to more easily hear any grunt, pressure is placed upwards on the ventral body wall caudal to the xiphoid sternum. In a small cow it may be possible to carry this out using a closed fist, while in larger animals a pole is placed just caudal to the xiphoid sternum and lifted upwards sharply by an assistant on each side. Several attempts should be made to elicit a grunt and pressure should be placed on the ventral abdomen and both sides from the xiphoid sternum to the region of the umbilicus to ensure that points of pain are detected. (B207.5.w5)
  • With acute localised pain (e.g. associated with traumatic reticuloperitonitis), while listening over the trachea with a stethoscope, to more easily hear any grunt, the withers are pinched. (B207.5.w5)
  • For the anterior abdomen (pain associated with localised peritonitis caused by traumatic reticuloperitonitis or abomasal ulceration), percussion, deep palpation, pinching of the withers and pressure on the xiphoid may be used. (B351.30.w10)
  • For the ventral abdomen percussion and application of pressure to a localised area may be used for localisation of pain associated with rumenitis, rumen abscessation, perforating abomasal ulceration. (B351.30.w10)

Pain associated with mastitis:

  • Allodynia may be such that even gentle touching of the affected udder is resented, being felt as painful. (B322.4.w4)

NOTE: Relief of pain by correction of a lesion is also part of clinical examination and diagnosis. (B207.2.w2)

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Physiological Evidence of Pain

Whenever possible, a combination of behavioural and physiological signs should be used for the assessment of pain. (P61.62.w3)
  • It is probable that pain cannot occur without stress (although stress may occur without pain). (J290.21.w1)
    • The association between pain and stress makes interpretation of physiological signs as being purely pain-related difficult. (J290.21.w1)
  • Measurement of physiological changes in the sympathetic adrenomedullary system or the hypothalamic-pituitary-adrenocortical (HPA) system does not directly measure pain, but does indicate how unpleasant the painful experience is. (J10.48.w4; P61.62.w4)
Activity in afferent nerves:
  • It has been shown that afferent activity from nociceptors in the testes and tail increased significantly following castration and tail docking with rubber rings in lambs. (J284.75.w1)
  • The time course of the increase in nociceptor activity correlates with increases in plasma cortisol and in abnormal behaviour. (J284.75.w1)

Activity of the sympathetic nervous system.

  • The sympathetic adrenomedullary system is primarily concerned with the rapid "flight or fight" responses; these are reflected in measurable changes in heart rate, levels of circulating adrenaline and noradrenaline and related parameters. (P61.62.w4) 
    • Measurements of this system may be most useful as an indicator of responses in the first five minutes after a noxious procedure has been implemented. (P61.62.w4)
  • This may be measured by changes in heart rate, pupil diameter, skin resistance and peripheral blood flow. (J284.75.w1)
  • Heart rate may be monitored by electrocardiogram. (J284.75.w1)
  • Changes consistent with predicted pain have been detected in animals following castration. (J284.75.w1)
    • The heart rate is also affected by variables such as eating, exercise and noises; these additional factors which may affect heart rate decrease its usefulness as a practical means of assessing pain. (J284.75.w1)
  • Levels of circulating hormones such as adrenalin may be affected by pain. (J290.21.w1)
    • Serial measurements of plasma catecholamines may be used to assess the activity of the sympathetic nervous system.(J284.75.w1)
  • Noradrenaline release, probably by damaged tissues, occurs in response to traumatic injury and may also be measured. This response occurs more slowly than adrenalin release but faster than the responses of the hypothalamic-pituitary-adrenocortical system. This response may be detected for up to about one hour. (P61.62.w4)

Activity of the hypothalamo-pituitary-adrenal axis.

  • The hypothalamic-pituitary-adrenocortical (HPA) system initiates metabolic and anti-inflammatory responses which are longer lasting than those of the sympathetic adrenomedullary system. (P61.62.w4) 
    • Indices of activity of the HPA system include plasma levels of cortisol, adrenocorticotropic hormone (ACTH) and corticotropic releasing factor. (P61.62.w4)
    • In general, activity in the HPA axis increases in a graded way in response to the presumed noxiousness of various experiences. (J10.48.w4; P61.62.w4)
    • Measurement of activity in the HPA axis are more likely to be useful after the first few minutes following a noxious procedure, and for several hours after the procedure has been completed. (P61.62.w4)
      • The response time of the HPA axis is such that this is insensitive for use as an index of distress elicited in the first few minutes after an insult. (J10.48.w4)
  • Plasma cortisol concentration is measured most commonly; the magnitude of the cortisol response usually agrees with the predicted degree of noxiousness of a procedure. (P61.62.w4)
    • Care is required when interpreting cortisol responses at the lower extreme of the response range. (P61.62.w4)
    • Care is required when interpreting cortisol responses at the higher extreme of the response range. Different noxious stimuli, applied at the same time as one another, may not have additive effects on cortisol responses, therefore the overall noxiousness of two such stimuli applied simultaneously may be underestimated. (P61.62.w4)
  • Levels of circulating hormones such as cortisol and vasopressin may be affected by pain. (J290.21.w1)
  • Levels of corticosteroids in plasma or saliva may be measured to most easily monitor activity.(J284.75.w1)
    • It is necessary to make a series of measurements both before and after the potentially painful stimulus, in order to accommodate the characteristics of corticosteroid release and elimination and to determine the changes. (J284.75.w1)
  • It has been shown that plasma cortisol concentrations closely follow the time course of changes in posture and activity seen after castration and tail docking. (J284.75.w1)
    • Interfering variables include individual variation, diurnal changes and other stressors which activate the hypothalamo-pituitary-adrenal axis. (J284.75.w1)
  • Changes in plasma cortisol levels have been used for evaluation of the magnitude and duration of (pain-associated) distress caused by castration, dehorning and tail docking in cattle. (J10.44.w2) 
    • Studies indicate that changes in the plasma cortisol concentration are suitable as an index of acute pain-induced distress. (J24.76.w3)
    • Problems with plasma cortisol measurements include difficulties in interpretation in the absence of other reliable indicators of pain and distress. (J21.66.w1)
  • There are individual animal-specific differences in cortisol responses: some individuals will consistently show high responses to a given stimulus while others will consistently show low responses to the same stimulus. (P61.62.w4)
  • It is important to consider variable effects of different stressors acting on individuals prior to a procedure being carried out, by comparing cortisol levels measured before the treatment with non-stressed levels, and whether or not they return to non-stressed levels. (P61.62.w4)
  • Note: a return of cortisol concentrations to pretreatment levels at the end of the acute response following a noxious stimulus does not necessarily indicate that the individual is free of pain at that time. Rather it indicates that the noxious input, in relation to what preceded it, is insufficient to cause a rise in plasma cortisol. (P61.62.w4)

Physiological signs noticeable on clinical examination:

  • These are generally aspects of the (adrenergic) defence (flight or fight) reactions and may include any combination of: 
    • pupillary dilatation;
    • wide opening of the eyelids;
    • transient blood pressure increases or decreases;
    • heart rate increase;
    • respiratory rate increase and alteration of character (may be seen as gasping or panting);
    • whisker movements;
    • piloerection;
    • body temperature increase;
    • muscle tone increase;
    • sweating;
    • skin temperature changes;
    • rectum or para-anal sac evacuation. 

    (J3.118.w4, B325.w5, J4.213.w2, W513.Jun04.w1)

NOTE: Cardiovascular responses in response to pain, in association with other physiological disturbances such as dehydration, acid-base imbalance and/or toxic shock, may contribute to a fatal outcome of a condition. (B207.2.w2)

In cattle: 

  • Rapid shallow respiration may be noted in individuals with severe pain, including, for example, acute foot pain. (J3.118.w4, J3.72.w4, P54.2.w9)
  • Milk-drop may be seen. (J3.118.w4, P54.2.w9)
  • There may be an identifiable decrease in production in cows in pain. (J4.221.w4)
  • Increased heart rate may occur but this may also be raised in response to fever, toxaemia etc. (P54.2.w9)
  • Sweating is NOT a feature of pain in cattle. (J4.213.w2, W513.Jun04.w1)

In sheep:

  • Rapid shallow respiration may be noted in individuals with severe pain. (J3.118.w4)
  • Hyperventilation may be seen in lambs following castration and tail docking. (B325.w6)

In goats:

  • Rapid shallow respiration may be noted in individuals with severe pain. (J3.118.w4, J4.221.w4)
  • Rapid respiration with abdominal splinting can be seen in response to visceral pain. (B322.4.w4)
  • Tachycardia in response to visceral pain. (B322.4.w4)
  • Decreases in production and loss of body condition are seen rapidly in dairy goats in pain. (J4.221.w4)

Data from experimental situations:

  • In calves subjected to hot-iron disbudding without analgesia, a raised heart rate, raised plasma cortisol levels, delayed return to rumination, reduced frequency of rumination and behavioural signs of pain such as head shaking and ear flicking were recorded. It was noted that the cortisol response was relatively short lived (30-60 minutes) compared with the raised heart rate (213 minutes) or the behavioural signs (hours). (J35.158.w2)
  • Since sedatives such as xylazine and butorphanol are known to reduce heart rate, heart rate is not an appropriate parameter to measure as an indicator of analgesic effect of these drugs. (J35.158.w2)
  • In experiments on castration and tail-docking of lambs using rubber rings, heart rate, and systolic, diastolic and mean arterial blood pressure, all remained raised for longer than did either ACTH or cortisol, indicating that heart rate and blood pressure measurements may be more sensitive indicators of pain than ACTH or cortisol measurements. (J10.50.w1, P61.62.w4)
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Response to Analgesics

"The ability of analgesic or anti-inflammatory drugs to reverse signs of pain can provide a powerful diagnostic aid." (B325)
  • The peripheral nociceptive basis of acute pain may be confirmed by reduction in behavioural and physiological changes indicative of acute pain on treatment of the affected tissues with local anaesthetic. (J284.75.w1)
  • Provision of post-operative analgesia either just before or just after recovery from general anaesthesia may reduce morbidity; this indicates that the animal may otherwise have experienced pain. (P54.2.w15)
  • It is a reasonable assumption that "If analgesics improve a "situation", it was pain that the animal experienced." (P54.2.w16)
Response to analgesics may be a useful diagnostic aid indicating the presence of pain. (B325.w5, J284.71.w1) 
  • If a particular behaviour is thought to be caused by pain and when an anaesthetic or analgesic is given the behaviour is eliminated, it is reasonable to consider that the behaviour was due to pain. (J284.71.w1)
    • To an extent this argument is circular, since it is stating that the signs of pain are those which are normalised by administration of analgesics. (J290.21.w2)
  • If it is uncertain whether or not an animal is in pain, for example post-operatively, the response of the animal to a single administration of an analgesic may be used to assist in deciding whether or not analgesic treatment is required. (J4.191.w19)
  • However:
    • It is important to ensure that the analgesic agent does not in itself affect behaviour or prevent expression of pain. (J284.71.w1)
    • Most analgesics affect one or more of the physiological functions which may act as signs of pain; monitoring of physiological signs for pain assessment may be misleading in the presence of analgesics. (J290.21.w1)
    • There may be difficulties in assessing pain by the action of analgesic drugs such as opiates, NSAIDs or alpha-2 agonists if the effectiveness of the analgesic drug for a particular type of pain in the species in question has not been established. (J284.75.w1)

Examples of effects of analgesics:

  • Physiological and behavioural changes in response to castration/tail docking are reduced or eliminated by the use of local anaesthetics. (J284.75.w1)
    • This confirms that the acute pain associated with these procedures is based on peripheral nociception. (J284.75.w1)
  • Physiological and behavioural responses to tail docking has been reduced by use of xylazine, while the NSAID diclofenac was found to be effective against the pain caused by Burdizzo clamp castration but not that caused by either rubber ring castration or tail docking. (J284.75.w1)
  • Intrathecal morphine or etorphine did not affect responses to castration or tail docking. (J284.75.w1)
  • The visceral testicular pain caused by rubber ring castration may be resistant to alleviation by commonly used analgesic drugs. (J284.75.w1)
  • Although a response to analgesic therapy may be an excellent indication that pain had existed, it is known from studies of intractable pain in humans that the absence of such a response does not mean that pain is absent. (B323.3.w3)
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Assessment of Analgesia

  • The efficacy of analgesics may be tested objectively by an increase in the pain tolerance threshold of the animal. (P54.2.w16)
  • If a change in behaviour results from a procedure which is considered to be painful, and this change in behaviour is reversed by the administration of analgesics, then this is generally taken to indicate effective analgesia. (J290.21.w2)
    • It is important to consider the behavioural effects of the analgesic drug on normal individuals who are not in pain. (J290.21.w2)
    • Failure to include control, non-medicated individuals, when assessing the efficacy of an analgesic regime, may result in failure to detect than the analgesia is ineffective or insufficient. (J290.21.w2)
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Difficulties and Development of the Assessment of Pain in Animals

Development of methods for assessment of pain in animals has been delayed by the reluctance of some people to accept the fact that animals might experience pain in a similar way to humans. (J284.75.w1, )
  • Pain is a subjective experience and therefore direct measurement is not possible. It is necessary to make a value judgment, based on physiological and/or behavioural indices which provide indirect evidence of pain. Preferably several different indices should be used. Evaluation of indices for measurement of pain can be improved by training and by experience in their use. (J284.75.w1)

Changes in behaviour in response to pain reflect a complex integrated response and it is necessary to learn to interpret these changes in behaviour. (J4.221.w2)

  • Illness and depression may cause some behavioural changes similar to those seen associated with pain, which can make assessment of pain more difficult. (J4.221.w4)
  • Fear (particularly in non-domestic animals) may cause immobility which may be misinterpreted as indicating that the animal is not experiencing pain. (P20.1998.w2)

Many physiological measurements measure stress, which may be due to pain but can also be due to other stressors, such as isolation of herd animals, and restraint; this complicates interpretation of results. (J284.75.w1, J290.21.w1)

  • Some physiological indicators, such as heart rate, may be affected not only by pain and stress but also by a wide range of other factors including exercise and eating, which further complicates interpretation. (J284.75.w1)

Whenever possible, more than one means of assessment of pain should be used, for example combined use of behavioural and physiological measurements. (P61.62.w3)

Determining the site of origin of pain is recognised to be more difficult in animals than in humans who are able to explain where the pain is. (B207.2.w2)

Methods of assessment used in studies of pain:

Simple withdrawal reflexes, complex unlearned behaviours and learned behaviours may all be used in studies of pain in animals. (B326.14.w14, J297.22.w1)

Measurement of simple reflexes:

  • Simple reflex measures are commonly used for experimental assessment of pain, for example to demonstrate effectiveness of a method of analgesia. (B326.14.w14, J297.22.w1)
  • Disadvantages of the use of simple reflexes to measure pain include:
    • Simple reflexes are a measure of reflex activity rather than pain sensation; they do not measure the critical higher CNS functions which are involved in the experience of pain. (B326.14.w14, J297.22.w1)
    • Changes in either sensory or motor processing can cause an alteration in reflex activity. (B326.14.w14)

Measurement of complex (organised) unlearned behaviours:

  • These involve "a voluntary purposeful act requiring supraspinal sensory processing". (B326.14.w14)
    • These include, for example, paw-licking, prolonged withdrawal from a painful stimulus, guarding behaviours and vocalisation. (B326.14.w14, J297.22.w1)
    • Behaviours such as vocalisation may also be elicited by non-noxious stimuli. (J297.22.w1)

Measurement of learned behaviours:

  • These techniques use the fact that animals will seek to avoid aversive experiences, including pain, and appear to avoid places where painful procedures occur. (J284.74.w2, J297.22.w1, P61.62.w5)
    • Measurements can be made of, for example, the time taken for sheep to enter a race, and the degree of pushing required to make a sheep enter the race, after previous experiences of painful or otherwise unpleasant experiences at the other end of the race. (J284.74.w2)
    • By offering a choice (e.g. between two arms of a "Y", after different procedures have been carried out at the two ends of the "Y", relative aversion to different treatments can be measured. (J284.74.w2)
    • An important limitation is that the animals involved must learn to expect the aversive treatment. Therefore the effects are affected by the learning abilities of the animals and are difficult to use in assessment of procedures which are carried out only once, such as castration, dehorning or branding. (J284.74.w2, J288.28.w1, P61.62.w5)

Measurement of self-administration of analgesics:

  • This has been used in studies on lameness in broiler chickens, but has not been used in ruminants. (P61.62.w5)

Changes in nociceptive threshold:

  • This has been used to assess the presence of hypoalgesia or hyperalgesia in animals after application of routine surgical procedures, or associated with chronic painful conditions. (P61.62.w5)
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Authors & Referees

Authors Dr Debra Bourne MA VetMB PhD MRCVS (V.w5)
Referee A.B.Forbes BVM&S.,CBiol.,MIBiol.,DipEVPC.,MRCVS (V.w66); Dr H.R. Whay (V.w70)

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