Recognition and Treatment of Pain: In the Animal Welfare Act, a painful procedure is defined as, "... any procedure that would reasonably be expected to cause more than slight and momentary pain or distress in a human being..."

In both humans and most animals, the total pain experience results from an interaction between sensory pathways and the affective system, which provides the motivational and emotional component of pain. This varies considerably between species and individuals within a species.

Understanding the degree of pain involved in various experimental procedures provides an avenue of prediction of animal pain or distress. Physiological responses to pain can include increased blood pressure and heart rate, pupillary dilation, increased respiration, and an arousal response on the electroencephalogram. If baseline values are known for these variables, they can be monitored for changes.

To detect behavioral signs of pain, one must be familiar with the animal's normal behavior. It is worth a reminder that:  behavioral responses to pain vary between species, within species, and even within the same animal over different time points.

General behaviors that could be considered include: sleeping, feeding, drinking, locomotion, grooming, exploration, performance in learning and discrimination tasks, mating behavior, social interactions, and dominance/subservience responses within the social system.

Typical behavioral signs of acute pain:

• Protecting the painful area,

• Vocalizing (especially when handled or moving),

• Licking, biting, scratching, or shaking the painful area,

• Restlessness,

• Lack of mobility,

• Failure to groom

• Abnormal postures, or

• Lack of normal interest in surroundings.

Anthropomorphic Reflection of Potential Pain in Animals: Unless there is evidence to the contrary, assume that a procedure that causes pain in humans will cause pain in animals.

Other points to remember are:

• Abdominal surgery appears to be less painful in animals than humans, probably because most animals do not use their abdominal muscles for postural support (humans do use abdominal muscles for postural support). However, appearances can be deceiving.  Large animal abdominal surgery is more painful that small animal abdominal surgery, probably because of the increased abdominal contents weight of larger species.

• Lumbar and thoracic spinal surgery in animals also appears to be less painful than in man, probably due to man's postural requirements. However, procedures involving the cervical spine appear to be more uncomfortable in animals, than in humans.

• In animals, thoracic surgery involving the sternum appears to be more painful than surgery using a lateral intercostal approach.

• Surgery on the eye, ear or surrounding structures seems to elicit more signs of distress in animals than would be expected by comparing with human surgeries.  Signs such as head-tilt or shaking, or pawing or rubbing the area may be seen in animals, when the similar procedure in humans would not cause significant distress..

• Peri-rectal procedures seem to produce significant discomfort in animals (compared to humans). In addition to analgesia, protection of the affected areas is indicated in animals to prevent self or cage mate trauma.

• Surgery of the femur or humerus appears to be painful to most animals, and more painful that human experience, which may be due to trauma to the major muscle groups which overly these two bones.

• Animals in pain tend to distrust new taste or flavors, and if the association between a painful event and a new taste is made, the animal may refuse to consume it.  This is one reason why the use of analgesics administered AFTER the painful event had begun is often are often not as successful as analgesic administration BEFORE the development of pain (the phenomena of neophobia).

Influences of pain perception:

• Pain perception can be influenced by drugs, environmental, and behavioral factors. 

  • Practical application:  Always place analgesics on board before the painful event.

• Recovery in familiar surroundings may help to relieve distress and some pain.

  • Practical application:  Whenever possible, let the animal recover in its home cage.

• Acclimatization prior to a procedure may also facilitate recovery.

  • Practical application:  If  you'll be giving analgesics in the water, provide the treated water 3-5 days BEFORE the painful event to acclimate the animal to the taste of the medicated water.

  • Practical application:  If you are using testing chambers or restraining devices, place the animal in the device daily for 3-5 days BEFORE the test event and do nothing, to familiarize them to the chamber or device.

• The use of pre-emptive analgesia is a highly important concept to consider and employ!

  • Practical application:  Giving analgesic before anesthesia will decrease the amount of analgesic required, smooth the recovery, and decrease the amount of analgesic necessary post-procedure to control pain.

• The environment should be kept stable, minimizing stimuli that evoke a fearful response in the animal. Always handle the animal in an appropriate manner.

  • Practical application:  Kind and compassionate handling of the test animal will result in a calmer animal, less likely to bite or fight, and will provide more stable research data!

Various analgesics are available to the investigator to assist with pain management. When designing an analgesic section of the protocol, the investigator should consult Duke veterinarians who are experienced in animal pain management and elimination. Interaction of the analgesic with concurrently used drugs and the effect of the agent on study results must be considered when choosing the best agent for a given situation.