Rodent Fluid Regulation

BU IACUC Approved March 2009, Revised January 2014, Revised February 2019, Approved March 2019

Boston University is committed to observe federal guidelines and AAALAC International’s guidelines for humane care and use of animals.

This policy deals with fluid regulation as part of the experimental protocol. Experimental reasons for introducing fluid regulation fall into three main categories, as follows: (1) studies of homeostatic regulation of energy metabolism or fluid balance, (2) studies of the motivated behaviors and physiologic mediators of hunger or thirst, and (3) studies that regulate fluid consumption to motivate animals to perform novel or learned tasks.

It is recommended that principal investigators consult with a BU ASC veterinarian prior to submitting a protocol involving fluid restriction or regulation to the IACUC for review.


A. PI is required to consult with veterinary staff before starting a fluid regulation study.

B. Animals on fluid regulation or restriction must be monitored daily and findings documented daily using the hyperlinked form on this page (see Procedures section, below). Animals on fluid restriction must be weighed at least twice a week, at least 48 hours apart.

C. Rodents on fluid regulation or fluid restriction must be identified by a card on their cage. See Procedures section below for specifics on BU ASC MED vs CRC facilities.

D. Scheduling of fluid intake: Animals are given ad lib access to water at least:

  1. Once every 24 hours for one hour for rats, and
  2. Once every 12 hours for one hour for mice

E. Animals must be acclimated gradually, over a period of at least 3 days, to new restriction/regulation paradigms.

F. Fluid restriction must be limited to a carefully calculated minimum daily volume required to keep the animal healthy.

G. Before a fluid restriction study is started, it is mandatory that the ad lib daily fluid intake is determined for the exact same strain, sex, and age to evaluate their normal, ad lib fluid intake. Specifics for this requirement are detailed in the Procedures section, below.

H. “For both types of fluid regulation (scheduling vs. restriction), animals generally should be given free access to fluid for some period on days when experimental sessions are not scheduled, unless scientifically justifiable reasons preclude such fluid supplementation.”1

I. Planned duration of fluid regulation/restriction must be specified in the IACUC protocol.

J. No rodent can be completely deprived of fluids for more than 24 hours.

K. Research staff responsible for monitoring animals on fluid regulation studies must be trained and competent to evaluate the animal’s condition.

L. “In the case of conditioned-response research protocols, use of a highly preferred fluid as positive reinforcement, instead of restriction, is recommended.”5

M. The investigator must use “the least regulation/restriction that will achieve the scientific objective.”5

N. Young or growing animals are especially sensitive to fluid restriction, and placing these classes of animals on fluid regulation/restriction must be evaluated with a concern for their health and minimum growth requirements.

O. Fluid regulation for research purposes must be scientifically justified, and a literature search for alternatives must be performed.

P. Supportive care and interventional endpoints must be observed as specified in the Procedures section of this policy below or, if different, specified in the IACUC protocol.

Q. Depending upon the severity of the fluid regulation/restriction paradigm, the IACUC will consider assigning the animals to USDA Pain and Distress Category E.2

R. In case of Boston University Animal Science Center (BU ASC) finding a dehydrated animal, every effort will be made to contact the assigned research staff and principal investigator. However, if it is not possible to contact these individuals, the animal will be treated according to directions from the attending veterinarian or designee.



Consideration of the Species' Circadian Rhythm, Behavior, and Physiology


Species-Specific Considerations: Mice


Mandatory Determination of Ad Lib Fluid Intake Prior to Fluid Restriction Study — Procedures


Supportive Care and Interventional Endpoints — Fluid Restriction


Special Card on Cage Required for Rodents on Fluid Regulation or Restriction


Rodents — Scheduling of Fluid Intake


Rodents —Restriction of Fluid Intake


Scheduling: Scheduling access to fluid sources so an animal consumes as much as desired (ad lib), but only at regular intervals.

Restriction: The total volume of fluid consumed is strictly monitored or controlled and animals will not receive their complete daily ad lib ration.


BU IACUC Approved March 2009, Revised January 2014, Revised February 2019, Approved March 2019

Animal Care Revised Food Fluid Form

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