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 an animal and public health concern associated with the potential for the selection and dissemination of resistance in commensal bacteria and potentially zoonotic bacteria. To identify the extent of this situation, we built a risk model that provides a way to estimate the percentage of cross-contaminated feed in total and at the 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 produced in a country per year. The model, estimated that when antimicrobial medicated feed represents a hypothetical xi = 2% of the total feed produced in a country per year, then 5.5% (95% CI = 3.4%; 11.4%) of the total feed produced in a year could be cross-contaminated with different levels of antimicrobials due to practices related to medicated feed. In detail, 1.80% (95% CI = 0.2%; 7.7%) of the total feed produced in such a country would be cross-contaminated due to antimicrobial carryover occurring at the feed mill level, 1.83% (95% CI = 1.3%; 2.0%) at the transport truck level and 1.84% (95% CI = 1.2%; 2.0%) at the farm level. The model also demonstrated that even in cases where antimicrobial medicated feed would be produced in end-of-line mixers or a fine dosing system on trucks, the risk of cross-contamination would not be negligible; the percentage of cross-contaminated feed produced in a country (where xi = 2%) per year would be 3.7% (95% CI = 2.9%; 4.0%) and 2.4% (95% CI = 1.6%; 2.7%), respectively. It is hard to reduce the risk to zero as it is the result of factors occurring at different levels. Thus, the use of antimicrobial medicated feed should be avoided as much as possible to reduce selection pressure.