Complete Freund's adjuvant in laboratory animals: Reported welfare-relevant outcomes and alternatives-a scoping...

Complete Freund's adjuvant (CFA) is used in laboratory animals to stimulate strong immune responses. However, it can cause persistent local inflammation and tissue damage, raising welfare concerns. This scoping review aimed to (i) assess how frequently welfare-relevant outcomes are reported in CFA immunisation and antibody-production studies in mice, rats and rabbits; (ii) describe reported welfare-relevant outcomes and the methods used to assess them; (iii) chart CFA regimen details across studies; and (iv) summarise reported alternatives to CFA, including welfare comparisons where available. We followed a protocol registered in Systematic Reviews for Animals and Food and reported in accordance with PRISMA-ScR. We searched PubMed and Embase from 2015 onwards. Screening was conducted in two phases (title/abstract; full text) by one reviewer, with uncertainties resolved by a second reviewer. Data were charted on animal characteristics, CFA regimen details, welfare monitoring, reported local/systemic outcomes, analgesia/humane endpoints and comparator adjuvants. Of 1608 records screened, 689 were assessed at full-text level and 43 met inclusion criteria by reporting a welfare-relevant outcome (including 'no adverse effects'): local outcomes were reported in 24/43 and systemic in 8/43; structured pain or behaviour monitoring occurred in 4/43 and formal scoring in 1/43 studies. Alternatives were evaluated in 32/43; in studies involving head-to-head comparisons with CFA (28/32), alternatives were more often better tolerated (22/28) than similar (6/28), with efficacy usually comparable or higher (31/32). Despite well-recognised welfare concerns with CFA, welfare-relevant outcomes are rarely reported. Standardised reporting of CFA regimens, welfare assessment methods and results is needed to support evidence-based refinement and comparison with alternatives.