ACAPAC Policy Number: 2013-051
Policy Title: Justification of Number of Animals in protocols.

Purpose: For justification of the species and number of animals proposed, the Guide states that in the preparation of the protocol by the researcher and its review by the IACUC, whenever possible, the number of animals and experimental group sizes should be statistically justified [p, 25, 4th in a list of 15 items], and that while the responsibility for scientific merit review normally lies outside the IACUC, the committee members should evaluate scientific elements of the protocol as they relate to the welfare and use of the animals. For example, hypothesis testing, sample size, group numbers, and adequacy of controls can relate directly to the prevention of unnecessary animal use or duplication of experiments (p. 26). The Animal Welfare Act states that a proposal to conduct an activity involving animals must contain the following: (1) identification of the species and the approximate number of animals to be used; (2) a rationale for involving animals, and for the appropriateness of the species and numbers of animals [Regulations 2.31,e,1,2)]. This policy and companion SOP provide guidance on appropriate approaches to justifying the number of animals requested in protocols submitted to the Animal Care and Use Committees.


  1. Whenever possible, the number of animals and experimental group size should be statistically justified using power calculations based on previous research, published data, pilot studies, or prior experience.
  2. When statistical justification is not possible, explain briefly why statistical justification is not possible, and then provide a rationale for the proposed animal numbers, such as citations of previous research or prior experience.
  3. For a pilot study to test the variability of an outcome or to verify planned procedures, a brief rationale for proposed animal numbers should be provided when statistical justification is not possible.
  4. For teaching protocols, a brief rationale for proposed animal numbers should be provided based on previous experience or projected needs for students’ learning experience.
  5. A firm number (not a range) of animals must be given for a three-year period. You may list a maximum number. It is recommended that you consider including a 5-10% overage to cover cases where animals must be removed from your studies for nonexperimental reasons.
See Companion SOP for assistance.

Author: R. Sunde
ePublication Date: 1/11/2013