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Policy: Food Restriction for Rodents (IACUC)

Policy: Food Restriction for Rodents (IACUC)

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 which will ensure the animal's welfare and compliance with the approved proposal.
Food restriction may be based on weight of a complete diet or by energy content of a diet.

Background

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.

Food restriction is often used in behavioral experiments in which animals are food-deprived for a period of time and then tested in behavioral 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 body weight that promotes health and at the same time motivates 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 intake extended the lifespan of the rats and resulted in longterm improved health of the aged rats. Multiple studies show that ad libitum (AL) or free-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-tostudy 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 would not apply in certain conditions. The younger the animal, the greater the growth demands, the lower the body fat reserves, and the more significant the stress. Specific stages of the life cycle, including periods of pregnancy, lactation, birth to weaning, and post-weaning produce different metabolic demands. The most sensitive time of life for energy restriction is in the newborn and the period from birth-to-weaning. Restrictions imposed directly on the pups of >30% will produce significant and permanent stunting of lean tissue and bone growth. During pregnancy and lactation, restrictions have been used to study malnutrition and either the health of the pups or the dams. Rodents can maintain normal pregnancy with energy restrictions up to 50% of AL intake. Pups will be smaller at birth and permanently stunted and dams lose more body weight during pregnancy and lactation, but litter size is normal. Beyond 50% restriction, rodents will have high incidence of resorbed placentae. Energy restrictions up to 25% for the dam have minimal effect on the pups.

Guidelines

Guidelines for Scientifically Justified Food Restriction*

Description of Animal Parameter Monitored Justifiable Feed Restriction in Rodents
adult rodents >8 weeks of age body weight

>80% of initial body weight OR

>80% of age- matched, free-fed controls

food availability

 food provided at >50% initial ad libitum intake OR

food provided at > 50% ad libitum intake of age-matched controls

growing 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.

Exceptions

Food restriction for rodents in excess of these guidelines must be reviewed by the veterinary staff and referred to the IACUC for committee review and action as appropriate. 

References

1. Guide for the Care and Use of Laboratory Animals, NRC (2011).

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).

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Approved 5/4/2010
Updated: 7/9/2013

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