Unintended Veterinary Drug Residues in Feed from Upcycled Agricultural By-Products: A Hidden Threat to One Health and the Circular Economy

Abstract

The global food system faces an unprecedented challenge: feeding a growing population while reducing environmental degradation. Upcycling agricultural by-products and food waste into animal feed has emerged as a promising circular economy strategy, with potential to increase global food supply by up to 13% in calories and 15% in protein content while freeing 31–54 million hectares of cropland. However, this transition introduces hidden food safety threats, particularly unintended veterinary drug residues. This narrative review synthesizes current evidence on the sources, hazards, regulatory frameworks, and risk management strategies associated with veterinary drug residues in upcycled feeds. Residues enter circular feed systems through multiple pathways: carryover during feed manufacturing, contamination of processed animal proteins and distillers grains, environmental pollution from manure-amended soils, and animal-to-animal transfer. Public health consequences include direct toxicity (allergic reactions, hepatotoxicity, carcinogenicity), disruption of intestinal microbiota, and—most significantly—acceleration of antimicrobial resistance (AMR), projected to cause 10 million annual deaths by 2050. Regulatory approaches vary substantially: Japan, South Korea, and Taiwan recycle over 65% of food waste into safe animal feed through mandatory heat treatment (70–90°C for 30–60 minutes) and certification systems, while the European Union and United States recycle only 5–10% due to restrictive regulations. Key knowledge gaps include limited occurrence data for non-European by-product streams, insufficient understanding of residue fate through processing, and lack of empirical validation for long-term accumulation in closed-loop systems. The review concludes that realizing circular economy benefits without compromising food safety requires internationally harmonized action levels, risk-based monitoring of imported feeds, investment in rapid screening technologies, and adoption of successful certification models from Asian leaders.