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Determining which animals to include in the estimated number of animals in an animal-use protocol can be confusing to the investigator in the absence of IACUC-developed guidelines. The estimated number of animals that are kept for breeding purposes and not subjected to any experimental manipulations should be part of the animal-use protocol. That is in keeping with requirement to include animals “maintained but not yet used in experiments” in the USDA Annual Report of Research Facility. Each IACUC needs to develop practical guidelines about when to include young animals in the estimated number of animals. Instructions for USDA Annual Report of Research Facility do not specifically address breeding colonies except to note that animals that are used in experiments must be reported in the appropriate category.
If a study requires fertilized one-cell eggs, embryos, or fetuses, then the experimental-design section of the protocol should indicate the number of eggs, embryos, or fetuses that are required. But the estimated number of experimental animals should be limited to the number of female animals that are mated and euthanized or surgically manipulated to collect the required eggs, embryos, or fetuses. In this situation, males would be listed as breeders because they are not subjected to any experimental manipulation.
At what age to include suckling animals in the estimated number of animals is the next question. Requiring an investigator to include all animals born fails to recognize factors that result in stillbirths. Counting all live-born animals fails to recognize normal preweaning mortality. If a suckling animal will be subjected to any manipulation—such as thymectomy, toe-clipping or ear-notching for identification, tail-tip excision for genotyping, or behavioral tests—the estimated number of manipulated sucklings must be included in the number of animals used. If suckling animals will be euthanized at or before weaning because they are of the wrong genotype or sex for the experiment, they should be included as animals held but not subject to experimental manipulation.
One alternative is to instruct investigators to include all preweaning animals subjected to experimental manipulation in the estimated number of animals or for the IACUC to request estimated animal numbers as follows:
Estimated number of weaned and adult animals to be subjected to experimental manipulation