Endpoints in IACUC Applications

Experimental endpoints are defined as the points in time when the aims of an experimental study have been achieved and the study is concluded. In describing the design of a study, investigators should clearly define the objectives of the study, the expected timeline of experiments, the sequence of procedures, treatments and tests, and how long animals would be held under observation.

The study design should also provide information as to, how the procedures used may impact the health of the animals, and what behavioral observations and clinical criteria would be used to determine the health and well-being of animals.

Such criteria should be: i) objective, ii) appropriate for the species, iii) commensurate with the degree of invasiveness of procedures, and/or the potential for procedures to inducing pain and distress.

Humane endpoints refer to the point in time when a decision is made to remove an animal from an experiment or euthanize it. Such decisions should be made on the on the basis of a set of predetermined criteria indicating an irreversible deterioration in health conditions (e.g. loss of weight, loss of body condition, …), or behavioral evidence of severe pain and/or distress. In accordance with this definition, humane endpoints would always precede and supersede experimental endpoints.

Examples of humane endpoints criteria are: loss of body weight of 20%, body condition score (BCS) ≤2, cachexia, dehydration, recumbency, lethargy, respiratory distress, inability to reach food and water, lack of grooming, tumor size, tumor ulceration, persistent hypothermia etc).


  • Ullman-Cullere, M. Body condition scoring: a rapid and accurate method for assessing health status of mice. Laboratory Animal Science 1999, 49(3):319-323.)