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Policy: Food Restriction for Rodents (IACUC)
Policy: Food Restriction for Rodents (IACUC)
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 which 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.
Food restriction for research should be scientifically justified (NRC1 ). There is extensive literature on health benefits from some forms of food restriction. Welfare of the animals may be improved by a regimen of food restriction rather than ad libitum feeding.
Behavioral research often uses animals restricted from food for a period of time and then tested in tasks where food serves as a positive reinforcement. Either immediately after the test session or after a short delay, the animals are fed their ration of food that complements the amount of food consumed during the test session. The total amount of food eaten is typically held constant, or varied slightly, depending on whether the animal is above or below a specified target weight. Often rodents are maintained at 80-90% of their free fed body weights. In some cases, rats are given food rations adequate to maintain a particular healthy body weight and motivate the animals to work for food reinforcement. Studies involving use of food restriction often take months or even years to complete; therefore, a question that invariably arises is whether long-term food restriction regimens are healthy for rodents.
The literature provides a strong case that long-term restriction is, indeed, healthy. For rodents, the classic studies of McCay2 demonstrated that food restriction of post-weaning rats to approximately 50% of ad libitum (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 early onset of degenerative diseases, metabolic and endocrine disruptions, and diet-related tumors3. Furthermore, AL feeding of laboratory rats over a lifetime results in body fat levels that would be considered obese in humans, whereas food restriction to 75% of initial AL intake slows weight gain and allows a reasonable body fat content. Food restriction to 50% of initial AL intake results in a lean, but very healthy, rat4.
Research also shows that use of AL-fed animals introduces variability into experiments4, requiring use of larger numbers of animals which is contrary to government principles for animal use5. Examination of study-to-study variability in food consumption, body weight, and organ weights for the same strain or stock of rodent shows that AL-feeding results in tremendous laboratory-to-laboratory variability. The use of a nutritionally balanced diet, together with dietary restriction of up to 50% of AL intake, results in a better controlled rodent model with a lower incidence or delayed onset of metabolic and endocrine disruption, spontaneous diseases, and tumors. In addition, using a nutritionally balanced diet and moderate dietary restriction significantly improves survival, controls adult body weight and obesity, and reduces study-to-study variability, thus increasing the statistical sensitivity of expensive and long-term studies and ultimately reducing the number of animals that are needed.
Metabolic demands change across the lifespan, so these guidelines may not apply in certain conditions. The younger the animal, the greater the growth demands, and the lower the body fat reserves. Specific stages of the life cycle, including periods of pregnancy, lactation, birth to weaning, and post-weaning growth, produce 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 health of the pups or the dams. Rodents can maintain pregnancy to term with energy restrictions up to 50% of AL intake. Pups may be smaller at birth and permanently stunted and dams may lose more body weight during pregnancy and lactation, but litter size is expected to be normal. Beyond 50% restriction, rodents have had high incidences of resorbed placentae. Energy restrictions up to 25% for the dam have had minimal effects on the pups.
Guidelines for Scientifically Justified Food Restriction*
|Description of Animal||Parameter Monitored||Justifiable Feed Restriction in Rodents|
|rodents ≥8 weeks of age||body weight||
≥80% of initial body weight OR
≥80% of age-matched, free-fed controls
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||body weight||≥90% of body weight of agematched controls|
|pregnant dams||food availability based on restricted energy||food provided availability at ≥80% of ad libitum intake of pregnant control dam|
*Food restriction for rodents within these guidelines will not require discussion at a convened meeting of the IACUC. However, any IACUC member may call for any protocol to be discussed at a convened meeting for any reason. All food restriction is reviewed during the IACUC’s normal protocol review process.
Food restriction for rodents outside of these guidelines must be reviewed by the veterinary staff and the IACUC.
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 dietaryinduced 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).