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).


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

The University of North Carolina at Chapel Hill ("UNC-Chapel Hill" or "University") 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 (i.e., expected, part of the phenotype, and/or a humane endpoint) then research personal are responsible for monitoring and recording body weights as described in the approved protocol and at least weekly and more often for animals losing weight more rapidly. Some conditions or animal species may be evaluated by other means described in the approved protocol, such as Body Condition Score (BCS).  Evaluate according to the method and frequency recommended for that species or condition. 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-Chapel Hill IACUC Standard on Food and/or Water Restriction and/or Deprivation.)

The humane endpoint (euthanasia required) for body weight loss is 20% (as compared to the original body weight of an adult animal*).  Body weight loss may not exceed 20% without an approved Exception request (Section 8.)

*Consult with a DCM veterinarian for details regarding weight loss in obese animals or juvenile animals.

In conjunction with recorded weight loss, a rapid, practical, and objective health assessment is the BCS3,4. 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; however, the BCS will be decreased. Some species may be evaluated by BCS rather than body weight.

Links for relevant information for various species are listed below:

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

  • Anticipated weight loss equal to 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.
  • The humane endpoint (euthanasia required) for body weight loss is 20%.  This applies to free fed weight as part of conditioning experiments and other body weight loss studies. Body weight loss may not exceed 20% without scientific justification and an approved Exception request (see the UNC-Chapel Hill IACUC Standard on Exceptions).
  • 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. Body weight loss in growing animals indicates a more severe stress than a comparable weight loss in an adult animal. Therefore, veterinarians should be consulted for any anticipated weight loss greater than 10% in growing animals.

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-Chapel Hill 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.

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
Wed 2/14/24 11:54 AM
Effective Date
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10/20/2021 12:00 AM
Issuing Officer
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Vice Chancellor
Last Review
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10/18/2023 12:00 AM
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04/20/2022 12:00 AM
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10/18/2024 12:00 AM
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10/24/2019 12:00 AM
Responsible Unit
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Research-Institutional Animal Care & Use Committee