Assessment and Alleviation of Pain and Distress in Animals
Stress is a normal feature of life for all animals and serves important adaptive functions, such as flight-or-fight, predation, or "social-climbing." Animals used in research are subject to many stressors that are not normal and under circumstances that do not offer normal adaptive options.
Distress occurs when an animal is unable to adapt completely to a stressor (scientific definition).
Distress may be manifested by some behaviors and by biochemical and physiological changes; however, some animals hide fear and distress. It is critical, therefore, that protocols be designed to minimize the possibility of stress on the animals.
NOTE:* Behavioral, biochemical, and physiological changes indicative of distress can markedly affect research data; therefore, preventing distress in research animals is of prime importance, from both a humane and a research standpoint.
Possible stressors for animals being used in research:
- inadequate space and overcrowding
- social hierarchy
- social deprivation
- lack of environmental conditions needed for species-specific behaviors (e.g., gnawing for rats, exercise for dogs)
- inappropriate handling and restraint
- high-intensity lighting
- irregularities in temperature, humidity, and light cycles
- diet and feeding schedules
- experimental procedures
- and more
Response of an animal to a stressor can vary depending on age, sex, past experience (e.g., handling, previous experimental procedures), genetic profile, physiologic state, psychological state
Not all stressors can be treated with drugs, so planning experiments to minimize stress on the animals is of paramount importance.
Ways to reduce or eliminate distress
- careful attention to animal husbandry (i.e., light, temperature, humidity, caging, bedding, etc.)
- provision of species-appropriate environmental enrichment (in some species, this is mandated by law)
- social housing for social species
- training (of people AND animals)
- gentle, quiet handling
- limiting the numbers of stressors imposed on an animal
- use of anesthetics, analgesics, and anti-inflammatory drugs for intra- and postoperative or experimentally induced pain
Although we cannot know exactly what an animal perceives as painful, the rule of thumb is to consider any stimulus we humans would consider painful as also painful to animals
Use of anesthetics and analgesics
- required by law unless withholding is scientifically justified and IACUC-approved
- should be planned in consultation with an RARC veterinarian; must be planned while writing protocols
- use of paralytic drugs not permitted without anesthesia
- "surgical plane of anesthesia" = unconsciousness, immobility, and analgesia
- anesthetized animals must be monitored and the monitoring recorded
- there is NO one "perfect" anesthetic for all animals
Choice of anesthetic depends on species, procedure, available equipment, expertise with anesthetic regiment, goals of the experiment.
|cat||Decreases due to dehydration or inappetence||Increase in acute pain, Decrease in chronic pain||Increase in acute pain, Decrease in chronic pain||3rd eyelid protrusion, circumanal gland discharge|
|cattle||Decreases due to dehydration or inappetence||Increase in severe pain||Increase and shallow||teeth grinding, lack of grooming, violent when handled|
|dog||Decreases due to dehydration or inappetence||Increase in acute pain, Decrease in chronic pain||Increase in acute pain, Decrease in chronic pain||Increase in urine specific gravity, Decrease in volume, pupils dilated|
|guinea pig||dehydration||Increase||Increase||upper respiratory congestion|
|horse||dehydration||Increase||Increase, with flared nostrils||interrupted feeding with food held in mouth uneaten, pupils dilated, limb-shifting, reluctance to move|
|nonhuman primate||dehydration, no eating or drinking||Increase||Increase||looks "miserable," lack of grooming, glassy eyes|
|other birds||Decreases, dehydration||Increase||Increase|
|rabbit||inappetence (prolonged); dehydration||Increase||Increase||upper respiratory congestion|
|rodent||Decreases due to dehydration or inappetence||Increase||Increase||eats neonates; excessive licking and scratching, hunched posture, porphyrin around eyes in rats|
|sheep||Decreases due to dehydration or inappetence||Increase||Increase and shallow||grunting, grinding of teeth|
|swine||Decreases, will still approach food, dehydration||Increase||Increase||allow handling, hide in bedding|
Reprinted from Rollins and Kessel. The Experimental Animal in Research, Vol. 1., CRC Press 1990.
|cat||growl or hiss, but mostly silent||stiff, hunched in sternal recumbency, limbs tucked under body||reluctant to move, may carry limb||reclusive|
|cattle||grunting; teeth grinding||rigid; head down; back humped||limps; reluctant to move painful area||dull, depressed; act violent when handled|
|chicken||gasping||stand on one foot; hunched; huddled||none||lethargic; allow handling|
|dog||whimper, howl, growl||Increase in acute pain, Decrease in chronic pain||drag hind legs||subdued, quiet, restless, or vicious; varies from acute to chronic pain|
|guinea pig||urgent repetitive squeals||cower, crouch, recumbent||reluctant to move; walk in circles or pace||docile, quiet; or terrified, agitated|
|horse||grunting, nickering||rigid; head lowered; kicks at abdomen||favor area in pain||restless; agitated; an become aggressive|
|nonhuman primate||scream, moan, grunt||head forward, arms across body; huddled and crouching||excessive motion to tonic immobility, depending on pain severity||docile to aggressive|
|other birds||chirping||huddled; hunched and "fluffed up"||unwilling to move; unable to stand||inactive, drooping; miserable appearance|
|pig||increase in squealing to no sound at all||all 4 feet close together under body||inactive; drag hind legs||passive to aggressive, depending on pain severity|
|rabbit||piercing squeal on acute pain||hunched; face back of cage||Increase||apprehensive; dull; sometimes aggressive depending on pain severity; eats neonates|
|rodent||squeak, squeal||rounded back; head tilted; back rigid||ataxia; running in circles||docile or aggressive, depending on pain severity; eats neonates|
|sheep||teeth grinding; grunting||rigid; head down||limps, reluctant to move painful area||disinterested in surroundings; dull, depressed|
Reprinted from Rollins and Kessel. The Experimental Animal in Research, Vol. 1, CRC Press, 1990.