Animal Care and Use

Humane Endpoints and Relief of Pain and/or Distress Policy

Approved and Adopted: August 2023

IACUC Policy

Protocols involving pain or distress must include a humane endpoint and mechanisms to alleviate pain or distress through the appropriate use of analgesics, anesthesia, sedation, or euthanasia. Painful procedures/conditions are those that would be reasonably interpreted as painful or distressful for a human. Distress is defined as a situation where animals cannot readily adapt or a situation where they cannot escape an aversive stimulus.

Monitoring plans must be designed to promptly identify signs of pain or distress and provide for timely intervention. Monitoring personnel must be trained, familiar with species- or model-specific indicators of pain and/or distress, and must follow the monitoring plan described in the protocol.

Signs of pain may be different for each species or type of procedure performed. Monitoring parameters must be appropriate for the specific animal species or research model used. DCM veterinary staff will evaluate proposed monitoring plans and signs of pain and distress during submission review to ensure the parameters are appropriate for the species. Signs of pain and distress must be addressed with appropriate analgesic interventions unless an alternative approach is described and scientifically justified in the IACUC protocol.

Under the regulatory requirement to provide adequate veterinary care, the DCM veterinary staff have the authority to euthanize or treat animals determined to be in pain or distress. Reasonable attempts will be made to contact the responsible research personnel. However, if the lab is unavailable, an emergency response is required, or the parties disagree about the course of treatment, the Attending Veterinarian (AV) or designee has the authority to treat or euthanize animals.

Humane Endpoint Recommendations and Examples

These examples are not an exhaustive list and may not represent the most appropriate option for a specific combination of species and experimental model. Consult the DCM veterinary staff to identify species-specific or model-specific humane endpoints appropriate for inclusion in the IACUC protocol.

Commonly used humane endpoints for small rodent species (mouse, rat, hamster, guinea pig)

  • Weight loss of 20% (weighing schedule required with initial weight defined)
  • Failure to eat or drink, indicated by decreased food/water consumption or lack of feces/urine in the cage
  • Abnormal posture or position (hunched back, piloerection, guarding, or head-pressing)
  • Self-induced trauma (licking, biting, or scratching an injured site)
  • Seizures or paralysis
  • Lethargy
  • Moribund state (a clinically irreversible condition leading inevitably to death)

Commonly used humane endpoints for large animal species (NHP, dog, pig, rabbit):

  • Weight loss >10% (weighing schedule required with initial weight defined)
  • Failure to eat or drink, indicated by decreased food/water consumption or lack of feces/urine in the cage
  • Abnormal posture or position (e.g., lameness, guarding body parts, reluctance to stand)
  • Self-induced trauma (licking, biting, or scratching an injured site)
  • Seizures or paralysis
  • Lethargy

Signs of Pain and Distress

These examples are not an exhaustive list and may not represent experimentally validated indicators of pain and/or distress. Consult the DCM veterinary staff to identify species-specific or model-specific signs appropriate for inclusion in the IACUC protocol. General signs of distress in any species include decreased physical activity, change in response to human interaction, and decreased interest in food &/or enrichment items.

Commonly observed signs of pain or distress for small rodent species:

  • Decreased food and water consumption
  • Lack of urine/feces in the cage
  • Weight loss
  • Failure to thrive or gain weight in a growing animal
  • Persistent self-induced trauma (licking, biting or scratching an injured site)
  • Lethargy, especially if longer than 1 day
  • Poor grooming indicated by rough, dull, or matted hair coat
  • Abnormal posture or positioning
  • Distended abdomen
  • Diarrhea
  • Increased respiratory rate in an inactive animal
  • Vocalization when handled or other signs of aggression

Commonly observed signs of pain or distress for large animal species:

  • Decreased food and water consumption
  • Lack of urine/feces in the cage
  • Weight loss
  • Failure to thrive or gain weight in a growing animal
  • Persistent self-induced trauma (licking, biting or scratching an injured site)
  • Lethargy, especially if longer than 1 day
  • Abnormal posture or positioning
  • Distended abdomen
  • Diarrhea
  • Increased respiratory rate in an inactive animal
  • Vocalization when handled or other signs of aggression
  • Elevated body temperature

Commonly observed signs of distress for aquatic species:

  • Increased opercular movement
  • Abnormal location or orientation within the tank (e.g., unable to maintain level and upright buoyancy &/or minimal movement within the tank)
  • Disinterest in food
  • Color blanching

The IACUC has established humane endpoints and monitoring plans for the following models listed below:

Tumor Models in Mice and Rats

Monitoring plans for tumor models must include provisions designed to detect body wasting and tumor size. Weights must be measured and recorded at the start of the study and then weekly thereafter. However, since tumor growth can meet or exceed muscle wasting, body condition scoring (BCS) is a more accurate measure of the animal’s status. Monitoring schedules for BCS and tumor size can be tailored to the expected growth rate or disease model. For example, weekly monitoring until the tumor is palpable and then increasing to daily monitoring as animals approach the humane endpoint. Daily monitoring must include weekends and holidays.

Euthanasia is required if a tumor bearing animal reaches any of the following humane endpoints:

  • A tumor reaches 2cm in any direction in a mouse or 3cm in a rat
  • A tumor is growing in a location that interferes with a vital bodily function (eat, drink, ability to move around)
  • 20% weight loss when compared to their original body weight
  • Low body condition score. A score of 2 out of 5 requires DCM veterinary consultation. A score of 1 out of 5 requires euthanasia. See Appendix 1 for an example scoring system.
  • Significant cutaneous ulceration that does not resolve or is unresponsive to treatment

Ascites Method for Antibody Production in Rodents

Ascites will typically develop after 3 days. Starting 48 hours after injection, animals must be monitored daily, including weekends and holidays. Fluid must be removed when abdominal distention becomes evident. Abdominal paracentesis (abdominal tap) must not be performed more than three (3) times and the third procedure must be terminal.

Euthanasia is required in response to the following humane endpoints:

  • Persistent signs of tachypnea or dyspnea
  • Persistent signs of circulatory shock (rough coat, inactivity, pale ears, tachypnea, hypothermia)
  • Failure to relieve abdominal distension with paracentesis or evidence of solid abdominal tumor growth
  • Impaired movement to move around the cage

Lethal or Toxic Challenge (Rodent Species)

Acute Studies – Animals must be monitored (minimally, every 30 minutes) for the first two (2) hours following toxic challenge. After the initial phase of a stable response, animals must be monitored for signs of delayed toxicity once a day until the end of the observation period described in the protocol. Animals that reach the humane endpoint or a moribund state must be euthanized.

Monitoring records for lethal or toxic challenge studies must include the date and time (AM/PM) of the observations, the initials of the monitor, and any relevant observations. Monitoring records must be maintained for a minimum of six months following the experiment and provided to the IACUC or DCM veterinary staff upon request.

Death as an Endpoint (Rodent Species)

When scientifically justified in the IACUC protocol, certain studies (toxic challenge, infectious disease models) may include death as an endpoint. Animals participating in this type of study require the following:

  • Animals must have easy access to food and water. The IACUC recommends placing food or diet gels on the floor of the cage to meet this requirement.
  • Monitoring must be performed and documented twice a day. Monitoring sessions must be a minimum of 4 hours apart. The IACUC recommends monitoring in the early morning and late afternoon.
  • Animals exhibiting abnormal behavior must be removed from the group and housed individually. Dead animals must be promptly removed.

Monitoring records for death as an endpoint studies must include the date and time (AM/PM) of the observation, the initials of the monitor, and any relevant observations. The observations may include information about behavior, clinical complications, or the number of dead animals. Monitoring records must be maintained for a minimum of 6 months following the experiment and provided to the IACUC or DCM veterinary staff upon request.

Appendix 1.

Use frequent visual and hands-on examination of each animal to determine the body condition score. For the hands-on evaluation, allow the animal to rest on the cage’s wire top. Assess the vertebrae by palpation of the lumbar spine and the pelvic bones by palpation of the hips.