91´ÎÔª

Permissible Weight Loss for Animals Used in Research and Teaching

Number: IACUC-POL-016 

Responsible Office: Office of Research and Creative Scholarship (ORCS) 

Applies to: Principal Investigators Conducting Animal Research or All animal research and teaching protocols involving live vertebrate animals 

1. Purpose 

To establish institutional standards for monitoring body weight, defining permissible weight loss, and identifying required intervention points to ensure animal welfare and minimize pain or distress associated with research- or teaching-related activities.  

2. Policy  

Body weight is a critical indicator of animal health and well-being. All animals used in research or teaching must be monitored for changes in body weight when such changes may reasonably be anticipated due to experimental manipulation, clinical condition, or husbandry factors. 

Permissible weight loss limits, monitoring frequency, and intervention criteria must be clearly described and justified in the Animal Use Protocol (AUP) and approved by the IACUC prior to initiation of activities. Exceeding approved weight loss limits without prior approval constitutes noncompliance and must be reported to the IACUC. 

Unless scientifically justified and approved by the IACUC, animals may not be allowed to lose body weight beyond limits considered humane and consistent with accepted veterinary standards. 

3. Training 

All personnel responsible for animal monitoring must be trained to: - Accurately assess and record body weight and body condition, as applicable by species. - Recognize clinical signs associated with weight loss, dehydration, or poor body condition. - Initiate timely intervention and notification in accordance with the approved AUP and this policy.  

Training records must be maintained and made available to the IACUC and regulatory agencies upon request. 

4. Minimizing Pain and Distress 

Weight loss must be anticipated and proactively managed whenever possible. 

• Experimental designs should minimize unintended or excessive weight loss. 
• Nutritional support, dietary modifications, environmental enrichment, or supportive care must be implemented as appropriate. 
• Animals exhibiting clinical signs of pain, distress, dehydration, or poor body condition must receive prompt veterinary evaluation regardless of numeric weight loss thresholds.  

5. Procedure Guidelines  

Baseline and Monitoring Requirements 

• A baseline body weight must be obtained prior to the initiation of experimental manipulations. 
• Body weight monitoring frequency must be appropriate for the species, age, health status, and experimental design, and must increase when weight loss is anticipated. 
• Body condition scoring (BCS) should be used when validated for the species and may supplement or replace weight-based criteria when appropriate. 

General Permissible Weight Loss Limits (Absent Scientific Justification) 

Unless otherwise approved in the AUP: 

• Rodents and small mammals:
  • Up to 10% loss from baseline may be acceptable without intervention if animals are clinically normal. 
  • 10–15% loss requires increased monitoring and implementation of supportive measures. 
  • ≥15% loss requires veterinary consultation and intervention. 
  • ≥20% loss represents a humane endpoint and requires immediate veterinary consultation which generally requires euthanasia. Final determination is made by the Attending Veterinarian (AV). 
• Larger mammals (e.g., rabbits):
  • Up to 10% loss from baseline may be acceptable with close monitoring. 
  • >10% loss requires veterinary evaluation unless specifically justified and approved. 

Food or Water Restriction Studies 

• Restriction protocols must be scientifically justified and explicitly approved by the IACUC. 
• Target weights, duration of restriction, monitoring frequency, and intervention criteria must be clearly defined in the AUP. 
• Animals must be monitored at a frequency sufficient to ensure welfare is not compromised. 

Intervention and Humane Endpoints 

Intervention must occur when animals: - Reach or exceed approved weight loss thresholds. - Show clinical signs such as lethargy, dehydration, hypothermia, poor grooming, or reduced responsiveness. - Reach a body condition score indicative of compromised welfare. 

Interventions may include dietary supplementation, treatment, removal from study, or euthanasia, as approved in the AUP or as determined by the AV.  

6. Oversight and Compliance  

• The IACUC and Attending Veterinarian (AV) have authority to require modification or suspension of activities if weight loss exceeds approved limits or animal welfare is compromised. 

• Deviations from approved weight loss limits or monitoring plans must be promptly reported to the IACUC. 

• Records of body weight monitoring and interventions must be maintained as part of the protocol record.  

7. References 

1. Guide for the Care and Use of Laboratory Animals (NRC, 2010). 
2. AVMA Guidelines for the Euthanasia of Animals (current edition).  
3. Animal Welfare Regulations, 9 CFR 

8. Review, Approval and Version History 

Review and approval version history for this policy

Version	Date	Description of Changes	Approved By
1.0	January 13, 2026	Initial policy creation	IACUC Committee