Burying poultry carcasses on farms as a disposal option in crisis situations: learnings and perspectives from a field study during an avian influenza epizootic in France

Appropriate disposal of dead farming animals is required to guarantee effective disease control while protecting the environment. In crisis situations, alternatives to rendering can be used, including on-farm burial. The objectives of this study were to: (i) describe the burial and monitoring protocols used on poultry farms in France in response to major avian influenza outbreaks; (ii) assess the effectiveness of the burial protocol, in terms of both technical and biosecurity aspects, and microbiological, physical and chemical changes of the buried materials and the environment over time; (iii) provide recommendations for future burial and follow-up protocols. Five onfarm burial sites were monitored between March 2022 and March 2023, with at least four visits per farm. In addition to visual observations, soil, leachate, air and drilling water samples were collected, as well as boot swabs on/near the pit or on carcasses. For all five farms, microbiological analyses were performed to detect avian influenza virus (AIV), Clostridium botulinum and Salmonella spp. At one site, sampled drilling water was analysed to describe its physical and chemical properties. Visual anomalies were found at the sites over time, such as subsidence of the pits, presence of traces of wild and domestic animals, and rising to the surface of pieces of carcasses and feathers. AIV RNA was detected at all burial sites and in 4 % (8/201) of the collected samples. Viral genome was found up to nine months after burial on one farm. Clostridium botulinum was detected in 16 % (19/ 117) of the samples, whereas all samples tested negative for Salmonella spp. (0/109) at all sites and at all sampling points. All drilling water samples were compliant with drinking water standards. Our assessments demonstrated how the burial pits changed over time and the need to monitor them regularly so that corrective measures can be taken, if needed. In conclusion, our study can be used as a baseline for preparing better burial and follow-up protocols for future crisis situations. We recommend to standardise trench size and depth, to add mounding soil to the top of the pit and to set up a fence around. Proper pre-planning in peacetime will make it easier to meet the challenges associated with the management of repeated, high-frequency crises or crises of a new nature.