Behavioral research often requires that an animal perform a task for which it receives food or fluid reward. This situation is not unlike conditions in the wild, in which animals must forage, travel distances, solve problems, or otherwise work to obtain their food and water. In the professional judgement of many investigators, performing a task for rewards is behaviorally enriching for laboratory animals, especially nonhuman primates.
The purpose of this document is to provide investigators with guidelines for the proper use of diet control in behavioral studies.
Whenever an animal obtains any portion of its diet through food reward, the investigator must ensure that the sum of the nutritional value of the food earned through reward and of the food provided "free" (without the necessity of earning it) is sufficient to maintain the animal in a healthy state. Whenever possible, the food reward should be a "treat" (e.g., raisins, peanuts) which is sufficiently desirable and motivating for the animal that dietary restriction is unnecessary. However, dietary restriction may be justified in some cases, depending on the species, the behavioral task, and the requirements of the research proposal. In such cases, food must be provided every day, unless a specific exception to this policy has been obtained in an approved research proposal. In addition, weekly weight records must be kept, which should be available for examination by the veterinary staff and the ACUC.
If an animal under diet restriction loses more than 15% of its body weight (compared to its weight measured prior to the restriction) its food intake should be increased immediately until it regains its normal weight (+/- 15%). Exceptions to this policy will be allowed only if the attending or facility veterinarian determines that the weight loss does not endanger the health of the animal (as, for example, in the case of an animal that was initially overweight), or if prior approval has been obtained from the ACUC for the specific animal study proposal. Young, developing animals may have additional dietary requirements for maintaining their normal rate of growth; investigators working with young animals should specifically address this issue in their animal study proposal. The ACUC is aware that certain strains of large rats (e.g., Sprague-Dawley) may require up to a 20% loss of body weight before performing a behavioral task for rewards. Exceptions to the 15% maximum weight loss policy (up to a maximum of 20% weight loss) will be considered in such cases, but only if such strains are adequately justified in the animal study proposal.
As with food intake, whenever an animal obtains any portion of its fluid requirements through fluid rewards in behavioral testing, the investigator must ensure that the sum of the fluid earned through reward and the fluid provided "free" (without the necessity of earning it) is sufficient to maintain the animal in a healthy state. When water is not provided ad libitum, either the animal should be permitted to earn fluids to satiety during the period of behavioral training or its fluid intake should be appropriately supplemented on a daily basis.
In cases where supplements are required, the minimum amount of fluids to be provided daily should be equivalent to the amount typically consumed by the animal when either it is permitted to earn fluids to satiety or it is provided with water ad libitum. An exception to this policy will be made for the day immediately following a 24 hour or longer period in which the animal is provided with fluids ad libitum. On such days only, a reduced fluid supplement is permitted, but only if the normal supplement is demonstrated to interfere with behavioral training.
Assessment of adequacy of fluid intake
Even though animals typically learn to meet all of their daily fluid requirement during the testing session, a number of precautions must be taken to avoid the possibility of acute dehydration or chronic fluid deficiency. The type (e.g. water, fruit juice) and concentration, if applicable, of the fluid reward should be specified in the animal study proposal. Daily records of fluid intake must be maintained and be available for review by the veterinary staff and the ACUC. Each animal under fluid restriction will be observed daily for health status by the animal care staff. If the Institute veterinarian determines that an animal is dehydrated on the basis of either physical examination or clinical pathological measurements, the animal's fluid intake must be immediately increased. A small but chronic fluid deficiency, however, may occasionally escape detection by physical observation.
Such chronic fluid deficiencies often result in a loss of body weight due to reduced food consumption. Therefore, as a further precaution against chronic deficiency, the animal's weight must be measured and recorded at no less than weekly intervals. If an animal shows a loss in body weight of more than 15%, fluids must be increased appropriately. Exceptions to this policy will be allowed only if the attending or facility veterinarian determines that an animal is adequately hydrated and that the weight loss does not endanger its health or prior approval has been obtained from the ACUC for the specific animal study proposal.
Albee, R.R., J.L. Mattsson, B.L. Yano, and L.W. Chang (1987).
Neurobehavioral effects of dietary restriction in rats.
Neurotoxicology and Teratology 9: 203-211.
Descriptors: male Fischer rats, body weights, grip strength, body temperature, flash evoked potential, auditory brainstem response, somatosensory and cerebellar evoked responses, caudal nerve action potentials, cortical flicker fusion, Feed restriction protocol involved feeding 15 percent (mild) or 50 percent (severe) less feed than controls had consumed (ad lib) the previous day. Dietary restriction has significant effects on numerous behavioral and neurophysiological parameters that should be considered in the interpretation of data when body weight differences are present, diet restricted rats were more excitable while restrained for testing.
Driscoll, P., J.R. Martin, P. Kugler, and K. Baettig (1983).
Environmental and genetic effects on food-deprivation induced stomach
lesions in male rats. Physiology and Behavior 31(2): 225-228.
NAL call number: QP1.P4
Abstract: When Roman high- and low-avoidance (RHA/Verh and RLA/Verh) rats were individually housed in plastic cages with sawdust bedding and food-deprived (F-D) for 4-5 days, it was found that F-D RHA/Verh rats had more lesions than their unfasted controls and more lesions than F-D RLA/Verh rats. The lesions were mostly petechial in nature and located in the glandular portion of the stomach. Also, F-D RHA/Verh rats which were housed in the same room as the controls, as well as F-D RHA/Verh rats which were housed in a separate room with a strong food odor present, had more lesions than F-D RHA/Verh rats housed in the same separate room when there was no food odor, and when none of the rats present had access to food. When F-D RHA/Verh and F-D RLA/Verh rats were individually housed in metal cages with grid floors, however, a general increase in lesion scores resulted and differences between the two rat lines disappeared, as did differences among the room conditions. Also, many lesions were of an ulcerative nature and were located in the rumenal portion of the stomach. It was concluded that sensory (in this case olfactory, at least) and genetic factors are capable of playing roles in the induction of stomach lesions in rats, and that the type, extent and location of the lesions can depend upon whether or not the animals have access to sawdust bedding.
Descriptors: food deprivation, housing, odors, inbred rat strains, stomach ulcers, body temperature regulation, gastric acid secretion, purpura etiology, stomach diseases, wood, litter.
Hughes, J.E., H. Amyx, J.L. Howard, K.P. Nanry, and G.T. Pollard (1994).
Health effects of water restriction to motivate lever-pressing in rats.
Laboratory Animal Science 44(2): 135-140.
NAL call number: 410.9 P94
Abstract: The objectives of this study were to determine the degree of water restriction necessary and sufficient to motivate acquisition and performance of a lever-press response in rats and the physiologic and general health effects of chronic daily restriction. Parameters examined included: hematological and clinical chemistry, body weight, gross necropsy, clinical examination.
Hohenegger, M., U. Laminger, P. Om, A. Sadjak, K. Guttmann, and M. Vermes
(1986). Metabolic effects of water deprivation. Journal of Clinical
Chemistry and Clinical Biochemistry 24(5): 277-282.
NAL call number: RB40.A1Z4
Descriptors: dehydration, resuscitation, experimental disease.
Horne, T., A. Gutman, S.H. Blondheim, and H.B. Aronson (1982). Effects
of 24 hour food and water deprivation on biochemical variables in blood.
Israel Journal of Medical Sciences 18(5): 591-595.
Descriptors: humans, 2.5 fold increase in plasma free fatty acids, 2 fold increase in bilirubin, significant increases in serum sodium, chloride, total proteins, albumin, uric acid, phosphorous, alkaline phosphatase, and aspartate aminotransferase, decrease in serum glucose and triglycerides, no changes in urea, potassium, cholesterol, or calcium.
Kyriazakis, I. and C.J. Savory (1997). Hunger and thirst. In
Animal Welfare, M.C. Appleby and B.O. Hughes, (eds.), Oxon, UK and
New York: CAB International, pp. 49-62.
NAL call number: HV4711.A586 1997
Descriptors: nutrient requirements, animal behavior, animal welfare, hunger, thirst, definitions, measurements of hunger, sources of malnutrition, sources of undernutrition, restriction, deprivation, welfare problems, behavioral problems related to restriction, stress related physiological problems, farm animals, laboratory animals.
Laties, V. (1987). Control of animal pain and distress in behavioral
studies that use food deprivation or aversive stimuli. JAVMA
(Journal of the American Veterinary Medical Association)
NAL call number: 41.8 Am3
Descriptors: overview of food deprivation in behavioral studies, effects of feed restriction, effects of handling and injections, overview of studies where pain is being studies.
Levin, S., D. Semler, and Z. Ruben (1993). Effects of two weeks of feed
restriction on some common toxicologic parameters in Sprague-Dawley rats.
Toxicologic Pathology 21(1): 1-13.
Abstract: This study was intended to identify changes caused by short-term reduced feed intake in rats such as may occur with unpalatable feed or other forms of anorexia. For 2 wk, groups of rats (10/sex/group) were fed ad libitum (control group) or given 75% (mildly restricted group), 50% (moderately restricted group), or 25% (severely restricted group) of the amount of feed eaten the day before by controls. The control group and mildly restricted group grew steadily, but the terminal body weights of the mildly restricted group (both males and females) were only about 80% of controls. The moderately restricted group did not grow during the first week but grew slightly during the second week (terminal body weights about 65% of control). The severely restricted group lost weight throughout the study (terminal weight about 40% of control). Restricted groups exhibited hemoconcentration directly related to the degree of feed restriction. White blood cell counts were reduced (principally due to lymphopenia) in severely restricted rats. Platelet counts were decreased in all restricted groups. Total serum protein concentration was reduced (decreased globulins) in all female restricted groups and in the severely restricted males. The severely restricted rats had increased serum bilirubin, electrolyte derangements, and (in females only) decreased cholesterol. Thymus and liver weights (absolute and relative) were decreased in the moderately and severely restricted groups. All the feed-restricted groups had an increased incidence of superficial gastric erosions. The mildly and moderately restricted groups had slightly decreased hematopoietic tissue in sternal bone marrow, while the severely restricted group had bone marrow necrosis, thymic atrophy, and mild testicular degeneration. Findings in the severely restricted group were distinct from those in the other groups on the basis of their severity and were considered adverse. Changes in the mildly and moderately restricted groups were considered adaptive and innocuous since feed restriction of this degree has historically been associated with increased longevity and decreased disease incidence in chronic studies.
Levine, S. and A. Saltzman (1998). An alternative to overnight
withholding of food from rats. Contemporary Topics in Laboratory
Animal Science 37(3): 59-61.
NAL call number: SF405.5 A23
Abstract: Withholding of food overnight has been used for numerous experimental purposes, including to reduce errors of intraperitoneal injections by diminishing the size and weight of the gastrointestinal tract, to prepare for gavage or surgery, or to avoid the effects food in the gastrointestinal tract might exert on drugs or nutrients. However, withholding food overnight causes undesirable side effects including loss of body and hepatic weight and decreases in blood glucose concentrations. Withholding food from rats housed on bedding can also lead to ingestion of bedding. Providing rats with commercially available sucrose cubes overnight ameliorated these undesirable effects while still reducing the size of the gastrointestinal tract. Rats housed in cages without access to bedding had an additional reduction in weight of the gastrointestinal tract. Analysis of the results indicated that providing sucrose cubes overnight and reducing access to bedding was an effective alternative to overnight withholding of all food.
Descriptors: methods, food deprivation, fasting, digestive tract, drugs, body weight, hepatic weight, blood sugar, bedding, sucrose, liver, rats.
Preparation and Maintenance of Higher Mammals During Neuroscience
Experiments. Report of a National Institutes of Health Workshop, March 1991
. Bethesda, Maryland: DHHS, Public Health Service, National Institutes of
Health, 45 p.
NAL call number: HV4930.P74
Descriptors: prolonged non-survival recording procedures, survival anatomical procedures, perinatal procedures, food and water restriction, inducing neurological deficits, awake behaving preparations, animal care and use concerns, sample research protocols.
Ray, S. (1998). An alternative to water deprivation techniques in animal
learning studies. Animal Technology 49(3): 113-120.
NAL call number: QL55.I5
Abstract: Many laboratories use a period of water deprivation to motivate animals on a variety of water reinforced learning paradigms including aversive conditioning and maze learning tasks. Such procedures can lead to long periods without water and increase inter-animal variability in learning performance. Reported is an alternative procedure using sucrose rich drinks, or sucrose solutions, as a reward in maze and discrimination learning procedures with no prior water deprivation. An initial experiment compares performance over trials of a water deprived group of rats learning to negotiate a Y maze, and a group of genetically matched animals running an identical maze with no water deprivation. Both groups negotiating the maze for a sucrose reward. Results show that non-deprived animals showed teaming that was equally as good as the water deprived animals. Similar results were confirmed in a Lashley jump stand discrimination task. The ability to study learning in non-deprived animals may be of great interest in studies of learned behaviour after lesion or other surgical interventions, when periods of dehydration may affect the animal's health. Further, the development of non-deprivation motivated techniques will reduce the severity of many commonly employed rodent learning paradigms. These results may also offer a useful heuristic to explore learning paradigms without food or water deprivation schedules in other species.
Schwartz, E., J.A. Tornaben, and G.C. Boxhill (1973). The effects of
food restriction on hematology, clinical chemistry, and pathology in the
albino rat. Toxicology and Applied Pharmacology 25(4): 515-524.
NAL call number: 391.8 T662
Descriptors: body weight, blood enzyme levels, erythrocyte counts, hematocrit, alanine aminotransferase, alkaline phosphatase, blood glucose, platelets, blood urea nitrogen, leukocyte count, organ weight, sex factors, time factors.
Shimamura, T. and S. Trojanowski (1976). Effects of repeated deprivation
of drinking water on the structure of the renal medulla of rats.
American Journal of Pathology 84(1): 87-92.
NAL call number: 442.8 AM39
Descriptors: pathological changes in renal medulla, tubulointerstitial nephritis, dehydration.
Vermeulen, J.K., A. de Vries, F. Schlingmann, and R. Remie (1997). Food
deprivation: Common sense or nonsense? Animal Technology 48(2):
NAL call number: QL55.I5
Abstract: Overnight fasting (food deprivation) is a very common procedure in pharmacological research. One of the many reasons is to empty the animal's stomach. Solvay Duphar investigated the effects of overnight fasting and the possibility to shorten the period of the overnight fasting on male Wistar rats. In case of the effects being far-reaching (quality research and animal well-being), it might be necessary to develop an alternative method. This experiment fits very well in the concept of the 3 R's of Russell and Burch. The experiment used 24 male rats. There were four experimental units. The rats were deprived respectively for 0 hours (controls), 6, 12, or 18 hours. This was done during the dark phase of the (facility) light cycle. A balance plateau was used for registration of animal behavior. After the deprivation, the animals were anesthetized with halothane (N2O/O2) and killed by decapitation. Liver weight, stomach contents, and bowel contents were parameters to be measured. Food deprivation causes severe changes in physiology and behavior of the rat. After six hours of food deprivation, the rat already has an empty stomach. The use of fasted rats in experiments seems only to be permitted when the duration of food deprivation is as short as possible.
Descriptors: experimental methods, animal behavior, drinking, eating, locomotion, grooming, resting, physiological changes.
University of California at Irvine
Policy for Food or Fluid Restriction
University of Colorado Health Sciences Center, Animal Care & Use
Water and/or Food Restriction; To get to this policy, click on Care and Use Policies in the left frame on the web page.
University of Vermont, Institutional Animal Care and Use Committee
Food or Fluid Restriction, Definitions, Policies and Guidelines
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Last updated June 11, 2005