The risk of cross-contamination due to the use of antimicrobial medicated feed throughout the trail of feed from the feed mill to the farm

The cross-contamination of non-medicated feed with residues of antimicrobials causes a public and animal health concern associated with the potential for selection and dissemination of resistance in commensal and potentially zoonotic bacteria. To identify the extent of the situation, we built a model that provides a way to estimate the percentage of cross-contaminated pig feed in total and per different levels at which cross-contamination may occur (i.e. the feed mill, the transport truck, the farm), for different levels of antimicrobial medicated feed (AB MF) produced in a country per year.

The potential carry-over of AB traces was assessed from the feed mill to the transport truck and the storage and distribution at the farm. The model was thus subdivided in three modules, one for each level, and five exposure pathways were considered. It was built using @Risk^® software (Palisade Corporation^®) and was run at 10,000 iterations per simulation.

The model estimated that, given our assumptions, when a hypothetical level of xi=2% of the feed produced in a country per year is AB MF, C1i= 5.5% (95%CI 3.4%; 11.4%) of the total feed produced in a year (T1i) could be cross-contaminated with different levels of AB due to practices related to MF. In detail, 1.80% (95%CI 0.2%; 7.7%) of T_1i in such a country would be due to cross-contamination occurring at the feed mill, 1.83% (95%CI 1.3%; 2.0%) at the transport truck and 1.84% (95%CI 1.2%; 2.0%) at the farm level. The model also demonstrated that, even in cases where MF would be produced in end-of-line mixers or fine dosing system (FDS) trucks would be used, the risk would not be completely removed; the percentage of cross-contaminated feed produced in a country (where xi=2%) per year would be C_2i=3.7% (95%CI 2.9%; 4.0%) and C_3i=2.4% (95%CI 1.6%; 2.7%), respectively.

The model showed a real risk of cross-contamination of feed due to practices related to MF. The risk is hard to be fully removed and thus, the use of MF should be avoided as much as possible. The model demonstrated that a considerable risk of cross-contamination can be avoided when MF is not produced in the main mixing line of feed mills and when FDS trucks are used. But, even in cases where these scenarios would be implemented, the risk would not be completely removed given that sources of cross-contamination would still exist at the truck and farm levels and hence should not be overlooked. The model can be used to provide estimations for different levels of AB MF produced and for different policies applied and should then be informed with data after carefully considering the specific situation.

Disclosure of Interest: None Declared.