Humane Endpoint
What is a Humane Endpoint?
When an experiment is expected to result in extreme pain or distress to laboratory animals, criteria for terminating the experiment are required in order to enhance the ethics of animal experimentation and the reliability of the experimental results.
Even if an animal is not used in the experiment or the desired results are not obtained, objective criteria for humane termination are needed when the animal experiences unexpected pain or is unable to eat or move normally. These humane endpoint criteria must be presented when preparing the protocol.
For experiments that require confirmation of mortality, an animal judged to have reached a moribund state is regarded as dead and is humanely euthanized.
Humane Endpoint Using a Scoring System
The following is a scoring system and a Body Condition Score (BCS) system used to determine the humane endpoint.
[Table 2] Example of a Scoring System for Determining the Humane Endpoint
| Variable | Score | Criteria |
|---|---|---|
| Body Weight Change | 0 | Normal |
| 1 | <10% weight loss | |
| 2 | 10–15% weight loss | |
| 3 | >20% weight loss | |
| Body Condition Score (BCS) |
0 | BCS >3 |
| 1 | BCS >2 and <3 | |
| 2 | BCS >1 and <2 | |
| 3 | BCS 1 or below | |
| Appearance | 0 | Normal |
| 1 | Lack of grooming | |
| 2 | Rough coat, nasal/ocular discharge | |
| 3 | Severely rough coat, abnormal posture, dilated pupils | |
| Clinical Signs | 0 | Normal |
| 1 | Minor changes | |
| 2 | 1–2℃ change in body temperature, ~30% increase in heart rate and respiratory rate | |
| 3 | Change in body temperature exceeding 2℃, ~50% increase or sharp decrease in heart rate and respiratory rate | |
| Behavior | 0 | Normal |
| 1 | Minor changes | |
| 2 | Abnormal, reduced movement, reduced alertness, inactive | |
| 3 | Distressing vocalization, self-mutilation, almost no movement | |
| Response to External Stimuli |
0 | Normal |
| 1 | Mildly depressed/increased response | |
| 2 | Moderately abnormal response | |
| 3 | Aggressive response or comatose state |
** If the total score is 5 or higher, or if any single item scores 3 points, humane euthanasia must be performed following evaluation by a veterinarian. This scoring system must be applied appropriately to the animal experiment plan and animal model, and must be modified for the specific animal species.
[Figure 1] Body Condition Score (BCS) System in Rodents
| BCS | Mouse | Rat |
|---|---|---|
| BC1 Emaciated/Debilitated |
Skeleton prominently protrudes. Almost no flesh. Vertebrae are markedly separated and visible. | Segmentation of the vertebrae is prominent. Almost no flesh covering the pelvic bones. The pelvic bones markedly protrude. Segmentation of the caudal vertebrae is clearly visible. |
| BC2 Under-conditioned |
Separation of the protruding vertebral column is visible. Dorsal pelvic bones are easily palpable. | Segmentation of the vertebrae is prominent. Thin skin and subcutaneous fat cover the pelvic bones, which are easily palpable. The caudal vertebrae are also covered by thin skin and palpable with light pressure. |
| BC3 Well-conditioned |
The vertebral column and pelvic bones are not prominently visible and are palpable when slight pressure is applied. | Segmentation of the vertebrae is easily palpable. Adequate subcutaneous fat covers the pelvic bones, palpable with slight pressure. There is adequate fat at the tail base, and the caudal vertebrae are not prominent but are palpable. |
| BC4 Over-conditioned |
The dorsal bones are continuous without segmentation. The vertebrae are palpable only when firm pressure is applied. | Segmentation of the vertebral column is palpable with slight pressure. The pelvic bones are surrounded by thick subcutaneous fat and palpable only with firm pressure. The fat tissue at the tail base is thick, and the caudal vertebrae are difficult to palpate. |
| BC5 Obese |
The mouse appears flat and bloated. The skin and subcutaneous fat tissue are thick, and the skeleton has disappeared. | Segmentation of the vertebrae is palpable only with firm pressure or appears continuous. The pelvic bones are surrounded by thick subcutaneous fat tissue and difficult to palpate. The fat tissue at the tail base is thick, and the caudal vertebrae are difficult to palpate. |
* Record the BCS using '+' and '-'. For an additional increase, record as '2+' or '2-'.
Example of an Endpoint Using a Scoring System in Rodents
IACUC Standard Operating Guidelines, Table 3-2
| Score | Body Weight Change | Hair Coat | Eyes and Nose | Behavior | |
|---|---|---|---|---|---|
| Activity | Posture | ||||
| 0 | Normal weight | Normal | Normal | Normal | Normal |
| 1 | 10% weight loss | Rough hair coat | Eyes squinted or closed | Reduced response to mild stimuli and reduced activity | Sits in a hunched posture |
| 2 | 20% weight loss | Rough and unkempt hair coat, hair loss occurs | Eyes squinted or closed. Swelling around the eyes, porphyrin staining observed | No response to stimuli and no movement | Sits hunched on the floor, head positioned on the floor |
| 3 | 30% weight loss | - | - | - | Frequently lies on the floor |
※ If the total of each item, including clinical signs, is 8 points or higher, or if the maximum score is recorded in two or more items (e.g., body weight change 3 points and hair coat 2 points), euthanasia is performed.
Example of an Endpoint Based on External Clinical Signs
IACUC Standard Operating Guidelines, Table 3-3
| External Clinical Sign | Field of Application | Humane Endpoint |
|---|---|---|
| Size/degree of tumor | · Subcutaneous/intraperitoneal tumor experiments · Hybridoma experiments |
· When the tumor exceeds 10% of body weight · When necrosis, infection, or ulceration interferes with feed intake or water consumption |
| Anorexia and continuous weight loss | · Disease metastasis or chronic infection experiments | · When body weight rapidly decreases by 20% or more of normal weight |
| Inability to walk | · Various research fields | · When the time spent in a recumbent posture increases |
| Severe organ-specific or systemic symptoms | · Toxicity testing · Systemic disease induction experiments |
· Peripheral nervous system: when muscle weakness or spastic paralysis is observed · Central nervous system: circling, blindness, dementia, convulsion, etc. |
| Hypothermia | · Infectious disease research · Vaccine potency testing |
· A 4–6℃ drop in body temperature in rodents |
| Imminent death (moribund state, etc.) | · Various research fields | · When characteristic clinical signs appear at the pre-mortality stage |