When experimental situations require food or fluid restriction, at least minimal quantities of food and fluid should be available to provide for development of young animals and to maintain long-term well-being of all animals. Restriction for research purposes should be scientifically justified, and a program should be established to monitor physiologic or behavioral indexes, including criteria (such as weight loss or state of hydration) for temporary or permanent removal of an animal from the experimental protocol (Van Sluyters and Oberdorfer 1991). Restriction is typically measured as a percentage of the ad libitum or normal daily intake or as percentage change in an animal’s body weight.
If a study requires food and/or water deprivation, it must be carefully controlled by frequent observation of the animal’s condition and behavior. Precautions that should be used in cases of fluid restriction to avoid acute or chronic dehydration include daily recording of fluid intake and/or recording of body weight at least once a week (NIH 1990) – or more often, as might be needed for small animals, such as rodents. Special attention should be given to ensuring that animals consume a suitably balanced diet (NYAS 1988) because food consumption might decrease with fluid restriction. The least restriction that will achieve the scientific objective should be used. In the case of conditioned-response research protocols, use of a highly preferred food or fluid as positive reinforcement, instead of restriction, is recommended.
Reduction of body weight should take place over a long period with a gradual decrease in caloric intake. It is not acceptable to deprive food completely until the target weight is reached.
Water should not be totally withheld for a period exceeding 24 hours. Water restriction should not be prolonged to the point that clinical signs of dehydration occur (inelasticity of skin, rough hair coat, sinking of eyes into the orbit).
Food and water restriction of laboratory animals has considerable potential for stress. Daily recording of body weight should be used to evaluate progress.
Control animals of identical age and sex on free choice feed should be used to establish the normal body weight index. This is particularly important for animals in a growth phase of life.
NRC, (1996). Guide for the Care and Use of Laboratory Animals. Washington, DC: National Academy Press.