Policy

Food Restriction for Rodents

Type

Policy

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.

Management of caloric intake is an accepted practice for long-term housing of some rodents.1 For rodents, the classic studies of McCay2 demonstrated that food restriction of post-weaning rats to approximately 50% of AL intake extended the lifespan of the rats and resulted in long-term improved health of aged rats. Multiple studies show that AL-fed laboratory rodents suffer from the early onset of degenerative diseases, metabolic and endocrine disruptions, and diet-related tumors.3 Furthermore, AL feeding of laboratory rats over the animal’s lifetime results in body fat levels that would be considered obese in humans.

Research also shows that the use of AL-fed animals introduces variability into experiments,4 requiring the use of larger numbers of animals which are contrary to government principles for animal use.5 Examination of study-to-study variability in food consumption, body weight, and organ weights for the same strain or stock of rodents shows that AL-feeding results in laboratory-to-laboratory variability. The use of a nutritionally balanced diet, together with dietary restriction results in a better-controlled rodent model reducing study-to-study variability, thus increasing the statistical sensitivity and ultimately reducing the number of animals that are needed.

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.

Guidelines 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.

Description of Animal Parameter Monitored Acceptable Feed Restriction in Rodents Without Additional Justification
Rodents ≥ 8 weeks of age Bodyweight
  • ≥80% of initial body weight OR
  • ≥80% of age-matched, free-fed controls
Rodents ≥ 8 weeks of age Food availability
  • Food provided at ≥50% initial ad libitum intake OR
  • Food provided at ≥50% ad libitum intake of age-matched controls
Rodents <8 weeks of age Bodyweight ≥90% of body weight of age-matched controls
Pregnant dams Food availability based on restricted energy Food provided availability at ≥80% of ad libitum intake of pregnant control dam

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. Guide for the Care and Use of Laboratory Animals, 8th edition (The Guide), NRC, 2011. (https://www.ncbi.nlm.nih.gov/books/NBK54045/)
  2. McCay, C.M., Crowell, M.F. & Maynard, L.A. The effect of retarded growth upon the length of life and upon the ultimate body size. J Nutr 10, 63-79 (1935).
  3. Keenan, K.P., Hoe, C.M., Mixson, L., McCoy, C.L., Coleman, J.B., Mattson, B.A., Ballam, G.A., Gumprecht, L.A. & Soper, K.A. Diabesity: a polygenic model of dietary induced obesity from ad libitum overfeeding of Sprague-Dawley rats and its modulation by moderate and marked dietary restriction. Toxicol Pathol 33, 650-674 (2005).
  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 (https://oacu.oir.nih.gov/system/files/media/file/2021-02/b7_diet_control_in_laboratory_animals.pdf)

Approved Date

Revised Date