Food Restriction for Rodents

Policy

Rodents must be fed a nutritionally complete diet ad libitum unless adequate scientific justification for food restriction is provided in the animal use protocol. All protocols involving food restriction must include monitoring procedures that will ensure the animal's welfare. Food restriction may be related to animal body weight, weight or amount of an ad libitum diet, or energy content of a diet.

Background

The standard of care for laboratory rodents is to provide a nutritionally balanced diet to the animal at all times, which is referred to as feeding ad libitum (AL). When access to food is limited, either partially or completely, for >24 hours the animal is food restricted. Restriction of food intake may be required for some physiological or behavioral research. These studies should use the least restriction necessary to achieve the scientific objective while maintaining animal well-being.

The use of food restriction in rodent experiments requires evaluation of (1) the necessary level of restriction, (2) potential adverse consequences of restriction, and (3) methods for assessing the health and well-being of the animals during restriction1. The degree of food restriction that can be safely used depends on the species, strain, sex, and age of the animals. Animals should be closely monitored and excess weight, behavioral, or clinical changes used as criteria for removal of an animal from a protocol.

The degree of food restriction necessary for consistent behavioral performance is influenced by the difficulty of the task or the motivation required of the animal. In the case of conditioned-response research, the use of a highly preferred food or fluid as positive reinforcement, instead of restriction, is recommended1.

Metabolic demands change across the lifespan and stage of the life cycle. Pregnancy, lactation, birth to weaning, and post-weaning growth have different metabolic demands. The most sensitive time of life for energy restriction is the period from birth to weaning. Restrictions of >30% imposed directly on the pups will produce significant and permanent stunting of lean tissue and bone growth. During pregnancy and lactation, restrictions have been used to study malnutrition and the health of the pups or the dams. Energy restrictions up to 25% for the dam have had minimal effects on the pups. Rodents can maintain a pregnancy to term with energy restrictions up to 50% of AL intake although pups may be smaller at birth and permanently stunted.

Guide for Food Restrictions in Rodents

Food restriction within the following guidelines will be reviewed during the IACUC’s normal protocol review process but will not require discussion at a convened meeting of the IACUC. However, any IACUC member, for any reason, may call for any protocol to be discussed at a convened meeting.

Exceptions

Food restriction for rodents outside of these guidelines must be scientifically justified in detail in the IACUC protocol, will be reviewed by the veterinary staff, and will be called for Full Committee Review (FCR) by the IACUC.

References

1. Body Condition Scoring for Mice
2. Body Condition Scoring for Rats
3. Guide for the Care and Use of Laboratory Animals, 8th edition, NRC, 2011
4. Rowland, N.E. Food or fluid restriction in common laboratory animals: balancing welfare considerations with scientific inquiry. Comp Med 57, 149-160 (2007).
5. Health Research Extension Act of 1985. Animals in Research. Public Law 99-158, November 20 (1985).
6. Guidelines for Diet Control in Laboratory Animals