Permissible Weight Loss

Permissible Weight Loss

Approved March 22, 2001, revised October 17, 2013 (download)

Background: Weight losses may occur in research animals in association with a variety of experimental regimens including studies where feed and essential nutrients are withheld, such as studies of nutritional deficiencies, toxicology or cancer. Weight loss also occurs in association with many spontaneous diseases and is a prime indicator of declining clinical condition. Moderate food restriction and weight loss, rather than being detrimental, has been shown to promote health and extend the life of laboratory rodents and other species. The Institutional Animal Care and Use Committee (IACUC) has accepted weight losses of up to 20% as a humane limit. However, some studies (i.e., involving nutritional deficiency and tumors) may result in weight losses of greater than 20% that can be scientifically justified. Where possible, “performance based” testing has become more acceptable as a means of seeking a humane balance. For example, optimal or acceptable responses such as working for food rewards might occur with weight losses of far less than an arbitrarily accepted 20% weight loss limit. Such performance at lesser weight loss might also be achieved with a higher preference food reward.

Policy: The upper limit of acceptable weight loss in animals on experimental regimens shall generally be 20%. Written scientific justification must be provided to the IACUC for approval of a greater than 20% weight loss. In studies where weight loss is expected to occur, monitoring must be done by investigative staff trained and experienced in recognizing clinical signs of illness and distress in study animals. Weights must also be taken at least weekly under such circumstances and be readily available for review by the veterinary staff and the IACUC. In their protocol submissions, investigators must address situations where weight loss will exceed limits that are being proposed, and remedial measures that will be taken. Veterinary staff may intervene when such remedial measures prove ineffective or to address weight losses that occur in excess of 20% of pre-study body weight in any research animal, or when other limits approved by the IACUC have been reached or exceeded. Such intervention may include euthanasia. Exceptions to this policy will be allowed only if there is a veterinary determination that weight losses exceeding approved limits are not endangering animal health and well-being and scientific justification has been provided as part of an IACUC-approved protocol.

Criteria in addition to body weight measures might be used for rapidly growing animals, animals with tumors, or obese animals.  Body condition scoring can be used in addition to or instead of weight measures when appropriate.