Spontaneous disease in animals model for human conditions

WE welcome the government's Replacing Animals in Science Strategy1 and its clear commitment to accelerating the development and adoption of non-animal methods in research. We strongly support the ambition for the UK to be a global leader in this area. However, one important opportunity for replacement is not explicitly addressed: the role of naturally occurring, spontaneous disease in veterinary patients as translational models for human disease. Companion animals develop many complex disorders that closely parallel human conditions, including cancer, obesity, heart disease, osteoarthritis, endocrine disorders, infectious and immune-mediated diseases, and chronic kidney disease. These conditions arise in genetically diverse populations and progress over clinically relevant timescales. Importantly, companion animals share key environmental and lifestyle exposures with people, including diet, physical activity patterns, long-term medication use and ageing. Together, these features provide potential insights that induced laboratory models cannot readily replicate. The study of spontaneous disease in veterinary patients therefore represents a powerful opportunity for replacement, reducing reliance on purpose-bred experimental animals while directly aligning with the aims of the government's strategy. Recognising spontaneous veterinary disease as a legitimate and valuable alternative within the replacement landscape would strengthen the UK's scientific capability and help address acknowledged gaps where current in vitro and computational methods cannot yet capture whole-organism complexity. We therefore encourage policymakers and funders to explicitly incorporate spontaneous veterinary disease research into future implementation of the Replacing Animals in Science Strategy, and to ensure that appropriate funding mechanisms are available to support this work.