Purpose

This document provides guidance to researchers for determining and justifying appropriate animal numbers and species.

Policy

One of the IACUC’s charges under the Animal Welfare Act and the Public Health Service Policy on Humane Care and Use of Laboratory Animals is to review the investigator’s rationale for the number of animals and species of animals selected. Investigators must show that they are using the appropriate species and number of animals compatible with obtaining scientifically valid data.

Procedure

A.  Justification of animal numbers begins with a clearly-stated summary of the experimental design, including experimental animals, donor animals, and live-born offspring of pregnant animals and animals that are produced in breeding colonies, but cannot be used in research This justification must include information about the proposed experiment such as:

• The purpose of each experiment or set of related experiments,
• The number of experimental groups/subgroups,
• The number of animals by species/strain per group/subgroup,
• The number of animals necessary to provide sufficient tissues/cells.

B.  All animals involved in the study need to be included in the protocol.

C.  Potential animal losses due to morbidity, mortality or other difficulties with the experimental procedures must be described in order to justify the need for additional animals.

Justification of Animal Numbers

The IACUC recognizes that the basis for an appropriate justification of animal numbers depends largely on the nature of the study itself. The method by which the number of animals was determined must be clearly stated.

Basic types of studies are listed below, along with guidelines for justification of animal numbers appropriate for each type of study.

1. Teaching Protocols: Animal numbers are determined by a specified student-to-animal ratio, which must be explained in the justification narrative. Animal numbers should be minimized to the fullest extent possible without compromising the quality of the hands-on teaching experience for students.
2. Tissue Harvest Required for In-vitro Work (including antibody production): Animal numbers are typically determined by the amount of tissue/cells required and the number of individual animals needed to provide the appropriate amount of tissue/cells or antibodies, etc.
3. Exploratory or Pilot Studies: (use of live animals to demonstrate success or failure of a desired goal, such as the production of transgenic mice, proof of concept, or survey of a population): Animal numbers are typically justified based on the probability of the experimental procedure, and the PI’s experience and professional judgment.
4. Studies Requiring Inferential Statistical Analysis: If possible, animal numbers are determined by statistical power analysis. Alternatively, appropriate numbers of animals may be determined based on comparable studies for which the desired effect sizes were shown to be statistically significant.

Consultation with a statistician or use of statistical software during the design phase of the experiment may be useful. The UCD Center for Statistical Consulting can be contacted for assistance in estimating animal numbers in research proposals 530-752-6096; http://www-stat.ucdavis.edu/stats-lab/services.

Animal numbers cannot be justified on the basis of how many experiments the lab personnel can perform in a week, month, etc. The cost of the animal should not be used as a determining factor for the use of a particular species or model.

Procedure: IACUC-20
Date: 09/07/2006
Enabled By: PHS/USDA
Supersedes: 08/12/1999