ARRIVE Essential - Experimental animals

​​DISCLAIMER: Information on this and related pages is based on or copied directly from the ARRIVE guidelines 2019 (please see the original guidelines for more information, references and examples that are not included on these pages):

• updated guidelines for reporting animal research
• explanation and elaboration​

ARRIVE Essential 10 - Item 8 - Experimental animals

8a. Provide details of the animals used, including species, strain and substrain, sex, age or developmental stage, and weight.

The species, strain, substrain, sex, weight, and age of animals are critical factors that can influence most experimental results. Reporting the characteristics of all animals used is equivalent to standardised human patient demographic data; these data support both the internal and external validity of the study results. It enables other researchers to repeat the experiment and generalise the findings. It also enables readers to assess whether the animal characteristics chosen for the experiment are relevant to the research objectives.

Report age and weight for each group, include summary statistics (e.g. mean and standard deviation) and, if possible, baseline values for individual animals (e.g. as supplementary information or a link to a publicly accessible data repository). For most species, precise reporting of age is more informative than a description of the developmental status (e.g. a mouse referred to as an adult can vary in age from six to 20 weeks). In some cases, however, reporting the developmental stage is more informative than chronological age, for example in juvenile Xenopus, where rate of development can be manipulated by incubation temperature.

8b. Provide further relevant information on the provenance of animals, health/immune status, genetic modification status, genotype, and any previous procedures.

The animals’ provenance, their health or immune status and their history of previous testing or procedures, can influence their physiology and behaviour as well as their response to treatments, and thus impact on study outcomes. For example, animals of the same strain, but from different sources, or animals obtained from the same source but at different times, may be genetically different. The immune or microbiological status of the animals can also influence welfare, experimental variability and scientific outcomes.

Report the health status of animals in the study, and any previous procedures the animals have undergone. For genetically modified animals, describe the genetic modification status (e.g. knockout, overexpression), genotype (e.g. homozygous, heterozygous), manipulated gene(s), genetic methods and technologies used to generate the animals, how the genetic modification was confirmed, and details of animals used as controls (e.g. littermate controls).

Reporting the correct nomenclature is crucial to understanding the data and ensuring that the research is discoverable and replicable. Useful resources for reporting nomenclature for different species include:

• ​Mice - International Committee on Standardized Genetic Nomenclature[1]
• Rats - Rat Genome and Nomenclature Committee[2]
• Zebrafish - Zebrafish Information Network[3]
• Xenopus - Xenbase[4]
• Drosophila – FlyBase[5]

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