Veterinary antimicrobial stewardship is implemented across clinical environments that differ substantially in diagnostic capacity, prescribing routines, client or farmer relationships, organizational resources, economic constraints, guideline infrastructure, and regulatory expectations. Consequently, interventions with similar stewardship objectives may produce different prescribing responses across settings. This realist review examined how contexts interact with mechanisms to influence veterinary antimicrobial prescribing and stewardship outcomes. Searches conducted on 22 August 2026 generated 109 result instances; 46 duplicates were removed, leaving 63 unique records for screening. Thirteen records were excluded during initial screening and 12 after detailed eligibility assessment, yielding 38 included evidence units. Evidence was appraised for relevance, richness, and rigor and coded through context–mechanism–outcome reasoning, with attention to confirming, disconfirming, and context-dependent findings. The synthesis indicates that stewardship is unlikely to function as a simple consequence of guideline exposure or clinician knowledge. Diagnostic actionability, clinical uncertainty, prescribing habits, client or farmer negotiation, team organization, time, affordability, availability of feasible alternatives, and regulatory accountability can modify whether stewardship resources become usable in practice. Intervention evidence also indicates that improvements in selected prescribing behaviors, adherence measures, or intentions do not necessarily imply uniform reductions in antimicrobial use or improvements in clinical, welfare, resistance, or public-health outcomes. A refined program theory is therefore developed in which stewardship depends on context-sensitive activation of capability, opportunity, confidence, legitimacy, and practical feasibility. The resulting configurations are explanatory propositions rather than validated causal rules and require prospective testing across species, diseases, practice systems, and policy environments.
