Animal Care and Use

Fluid Regulation/Restriction for Large Animals

IACUC Policy

Created prior to 01/2012
Revised 05/2015

Scientific justification must be provided before the IACUC can approve any protocol requiring water restriction and/or deprivation. Furthermore, if approved by the IACUC, it is imperative that the least restriction that will achieve the scientific objective be used. 1


Water restriction/deprivation of research animals is sometimes necessary for behavioral training to meet specific scientific objectives. Research protocols that use fluid regulation can be divided into at least three main categories: 1) studies of homeostatic regulation of fluid balance; 2) studies of the motivated behaviors and physiologic mediators of thirst; and 3) studies that regulate fluid consumption to motivate animals to perform novel or learned tasks.2 Because these protocols have the potential for causing significant distress and can potentially adversely affect the health of the animals, guidelines have been established by the IACUC. Many neuroscience-related studies regulate the amount of fluid an animal receives as motivation (category #3 above) in experiments that require the animals to perform a behavioral task with a high degree of repeatability2, 3. However, fluid consumption is not an experimental variable in these types of studies. Rather, fluid regulation is used to motivate the experimental animals to perform the specific behavioral task(s) for water or other type of fluid reward. The regulation of fluid consumption outside of the experimental session ensures response reliability to the fluid rewards during the experimental sessions (i.e., operant conditioning). The following questions should be considered by both the PI and the IACUC when considering a protocol regulating access to fluid to facilitate operant training:

  1. What type of fluid regulation is most appropriate for meeting the experimental goals?
  2. Are there alternative procedures that would accomplish the same desired behavioral task without instituting fluid restriction?
  3. How will fluid access be restricted and will it be possible to allow periodic ad libitum access to water?
  4. What is the proposed schedule for monitoring fluid restricted animals so that adverse effects will be quickly recognized?
  5. What are the endpoints for intervention with supplemental hydration, if needed?

When regulation of fluid consumption is deemed necessary for experimental behavioral motivation, access to fluid outside of the experimental setting must be regulated to encourage performance of the rewarded behavior.3 Fluid regulation of individual animals is generally accomplished by one of two different designs: “fluid restriction” and “fluid scheduling.” In the “fluid restriction” method, animals are given a pre-determined amount of fluid per day and may drink that volume over any length of time. In “fluid scheduling,” the research staff determines the time of day the animal has access to fluid, but the duration of drinking and the volume consumed are determined by the behavior of the animal. Regardless of which type of fluid regulation is used, fluid restricted animals should generally be given free access to fluid for some period on days when the experimental sessions are not scheduled, unless precluding fluid supplementation is scientifically justified.3

In general, the difficulty of the behavioral task to be learned is inversely proportional to the level of fluid restriction necessary to motivate the animal to do the particular experimental task. 2 When training animals for a new task, it is important to gradually introduce them to the concept that fluid availability is restricted or context-dependent (e.g., they will obtain fluid rewards while in the experimental apparatus). This will expedite the learning curve of the animal as well as decrease the amount of stress fluid regulation can cause to the animal. Because of individual variation in water requirements, average guidelines for water intake or urine output for the assessment of physiologic status for individual animals is not appropriate.


  1. Water restricted/deprived animals should be monitored daily for continued good health as judged by stability in body weight; stability of performance in the experimental protocol; development of signs of dehydration (decreased skin turgor, dry mucous membranes, sunken eyes, decreased urine output, urinalysis results, lab testing of blood samples); and signs of stress (e.g., changes in normal sleep cycles, abnormal conspecific social interactions, development of abnormal behaviors).
  2. Records should be kept at appropriate intervals by the research laboratory staff to assist the Division of Comparative Medicine (DCM) veterinary staff in monitoring for undesirable effects on the health or behavior of individual animals being fluid restricted. At a minimum, records should be kept for the daily fluid volume as well as frequent body weight data for all animals during periods of fluid restriction. These records should be readily available to the DCM veterinary staff as well as to the IACUC during its semiannual facility inspections.
  3. The DCM veterinary staff may decide that it is clinically necessary to suspend fluid restriction for individual animals based on clinical assessment and/or the results of laboratory tests (e.g., CBC/differential, serum chemistry panel, serum osmolality measurement).


  1. The Guide for the Care and Use of Laboratory Animals: 8th Edition. (Guide). National Research Council. 2011, p. 30-31.
  2. Toth, L. A., and Gardiner, T. W. (2000). Food and water restriction protocols: Physiological and behavioral considerations. Contemporary Topics in Laboratory Animal Science, 39(6),pp.9-17
  3. NIH. (2002). Methods and Welfare Considerations in Behavioral Research with Animals. Washington, D.C.: U.S. Government Printing Office.
  4. Orlans, F.B., Prolonged Water Deprivation: A Case Study in Decision Making by an IACUC, ILAR News, Vol. 33 pp. 48-52, 1991.
  5. Desimone, R., Olson, C., and Erickson, R. The Controlled Water Access Paradigm, ILAR News, Vol. 34, pp. 27-29, 1992.
  6. Hughes, J.E., et al., Health Effects of Water Restriction to Motivate Lever Pressing in Rats, Laboratory Animal Science, Vol 44, pp. 135-140, 1994.