Simple SummaryThe monitoring and assessment of animals is important for their health and welfare. The appropriate selection of multiple, validated, and feasible welfare assessment indicators is required to effectively identify compromises or improvements in animal welfare. Animal welfare indicators available can be animal based or resource based and collated together to form various assessment tools. The literature contains a wide variety of indicators; however, there is yet to be an ideal constellation of indicators for animal-based welfare assessment in small mammals. A systematic review was performed to identify and outline common animal-based indicators for animal welfare assessment in small mammals, specifically guinea pigs (Cavia Porcellus), mice (Mus musculus), rabbits (Oryctolagus cuniculus), and rats (Rattus norvegicus). This review aims to provide the basis for further research into animal welfare indicators for these species and their application to improve animal welfare assessment, management, and strategies.AbstractThe monitoring and assessment of animals is important for their health and welfare. The appropriate selection of multiple, validated, and feasible welfare assessment indicators is required to effectively identify compromises or improvements to animal welfare. Animal welfare indicators can be animal or resource based. Indicators can be collated to form assessment tools (e.g., grimace scales) or animal welfare assessment models (e.g., 5 Domains) and frameworks (e.g., 5 Freedoms). The literature contains a wide variety of indicators, with both types needed for effective animal welfare assessment; however, there is yet to be an ideal constellation of indicators for animal-based welfare assessment in small mammals such as guinea pigs (Cavia Porcellus), mice (Mus musculus), rabbits (Oryctolagus cuniculus), and rats (Rattus norvegicus). A systematic review of grey and peer-reviewed literature was performed to determine the types of animal-based welfare indicators available to identify and assess animal health and welfare in these small mammals maintained across a wide variety of conditions. The available indicators were categorised and scored against a selection of criteria, including potential ease of use and costs. This review and analysis aim to provide the basis for further research into animal welfare indicators for these species. Future applications of this work may include improvements to animal welfare assessments or schemes, guiding better management, and implementing future strategies to enable better animal welfare.