Standard on Weight Loss in Research Animals


University of North Carolina at Chapel Hill Standard on Weight Loss in Research Animals



The standards and procedures described below provide guidance to all researchers and animal handlers for managing potential weight loss that may occur due to experimental variables or conditions that could interfere with eating and / or drinking (e.g. difficulty with ambulation).

Scope of Applicability

All personnel engaged in the experimentation and/or monitoring of research animals with potential health issues, including weight loss.

The UNC-CH Institutional Animal Care and Use Committee (IACUC) expects that anyone involved in animal work at the University will comply with this Standard. Requests for exceptions to this Standard must be reviewed and approved by the IACUC.


The development of animal protocols that involve models or procedures resulting in body weight loss should include sufficient monitoring to track the weight loss adequately.

If weight loss is listed in the protocol (expected, part of the phenotype, and/or an endpoint) then body weights should be recorded weekly and more often for animals losing weight more rapidly. (Some species may be evaluated by other means, such as body condition, so evaluate according to the method and frequency recommended for that species.) Research personnel should maintain written records for each animal to document daily food and fluid consumption, hydrations status, and any behavioral and clinical changes used as criteria for removal of the animal from the protocol.1

One example of protocols involving weight loss is those that involve food or fluid restriction. The use of food or fluid regulation requires the evaluation of three factors: the necessary level of regulation, potential adverse consequences of regulation, and methods for assessing the health and well-being of the animals.1 In instances where weight loss is anticipated due to a restricted caloric intake, the research personnel should closely monitor animals to ensure that food and fluid intake meets their nutritional needs. (See the UNC IACUC Standard on Food and/or Water Restriction and/or Deprivation.)

The maximum percentage of body weight loss should not exceed 20% of its initial (or adult-sized) body weight. When a body weight loss of > 20% is anticipated, an exception should be requested (as detailed below.)

In conjunction with recorded weight loss, a rapid, practical, and objective health assessment is the body conditioning score (BCS)3,4. The BCS is particularly useful where there is a decrease in the body condition without a corresponding loss of body weight5. (For example, when a tumor is growing, the tumor growth may add to the animal’s weight, and off-set some of the weight loss, but the BCS will be decreased.) Some species may be evaluated by body condition, rather than body weight (ex. Aquatic species).

Links for relevant information for various species are listed below:

The following conditions apply when anticipating weight loss in research animals.

  • Anticipated weight loss over 10% due to experimental manipulation must be scientifically justified and described in the approved Animal Care Application (ACAP). The investigator must measure an initial baseline weight and must monitor and record subsequent weight loss.
  • Weight loss as part of conditioning experiments may be as high as 20% of free fed weight if justified and appropriately monitored.
  • Anticipated weight loss greater than 20% requires a request for exception to the IACUC policy (see the UNC IACUC Standard on Exceptions) and will only be approved by the IACUC under special circumstances and if scientifically justified.
  • Weight loss studies in obese animal models should be designed in consultation with a veterinarian. The veterinarian will assist with determining the goal weight as a greater weight loss may be necessary to achieve the study goals.
  • Developing animals have increased dietary requirements to ensure normal growth. Controlled diet, or other procedures causing weight loss, in growing animals may prevent normal growth while not resulting in an overall weight loss. Weight loss in excess of 10% in growing animals indicates a more severe stress than a comparable weight loss in an adult animal and should be brought to the attention of the veterinary staff.

The US Department of Agriculture (USDA) and Public Health Service (PHS) policies require proper documentation of animal care and use to assess compliance with research protocols and clinical care procedures. All records must be available for review at any time by IACUC and external regulatory officials. See the UNC IACUC Standard on Animal Monitoring and Record Keeping.


1 National Research Council (US) Committee for the Update of the Guide for the Care and Use of Laboratory Animals, Guide for the Care and Use of Laboratory Animals, 8th ed. (Washington, DC: National Academies Press, 2011).

2 National Institutes of Health, Office of Animal Care and Use, "Guidelines for Diet Control in Laboratory Animals."

3 Charmaine J Foltz and Mollie Ullman-Cullere, "Guidelines for Assessing the Health and Condition of Mice," Lab Animal 28, no.4 (April 1999): 28-32.

4 Mollie Ullman-Cullere and Charmaine J Foltz, "Body Condition Scoring: A Rapid and Accurate Method for Assessing Health Status in Mice," Laboratory Animal Science 49, no. 3, (June 1999): 319-323.

5 National Institutes of Health, Office of Animal Care and Use, "Guidelines for Endpoints in Animal Study Proposals."


Requests for exceptions to this Standard must be reviewed and approved by the IACUC. If your experimental procedure requires a significant deviation to this Standard, please amend your application(s) to include Addendum 8.0 Request for Exception to Policy.

You must indicate the following:

  1. a description of the exception;
  2. the rationale (provide scientific justification and/or justification based on animal welfare);
  3. the potential adverse effects/clinical signs resulting from the exception; and
  4. specify which (and the total number of) animals in the approved protocol that will be affected.

The IACUC will review your request at the next monthly meeting.


IACUC: Institutional Animal Care and Use Committee

DCM: Division of Comparative Medicine

University Standard: The minimum acceptable limits or rules used to achieve Policy implementation, enforceable by the IACUC.

Body Condition Score (BCS): An assessment of an animal’s weight and its relative proportions of muscle and fat.

Related Requirements

External Regulations and Consequences

University Policies, Standards, and Procedures

Contact Information

Contact Information Table
Subject Contact Telephone Email
Animal Health Questions DCM Veterinary Services 919-843-3407
Protocol Questions Office of Animal Care and Use 919-966-5569

Important Dates

  • Effective Date and title of Approver: 01/16/2003; UNC IACUC
  • Revision and Review Dates, Change notes, title of Reviewer or Approver: Revised 02/27/04, Revised 09/09/2011, Revised 04/2014, Placed on University Standard and links updated 09/2018; UNC IACUC

Approved by: UNC IACUC

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Article ID: 132216
Thu 4/8/21 9:26 PM
Tue 7/20/21 10:42 PM
Effective Date
If the date on which this document became/becomes enforceable differs from the Origination or Last Revision, this attribute reflects the date on which it is/was enforcable.
10/21/2020 12:00 AM
Issuing Officer
Name of the document Issuing Officer. This is the individual whose organizational authority covers the policy scope and who is primarily responsible for the policy.
Issuing Officer Title
Title of the person who is primarily responsible for issuing this policy.
Vice Chancellor for Research
Last Review
Date on which the most recent document review was completed.
10/21/2020 12:00 AM
Last Revised
Date on which the most recent changes to this document were approved.
10/21/2020 12:00 AM
Date on which the original version of this document was first made official.
10/24/2019 12:00 AM
Responsible Unit
School, Department, or other organizational unit issuing this document.
Research-Institutional Animal Care & Use Committee