Qualitative risk assessment of homogeneity, stability, and residual concentrations of antimicrobials in medicated feed and drinking water in pig rearing

Abstract Background Despite the common use of oral group treatment in pig rearing, the magnitude of the factors influencing the homogeneity and stability of antimicrobial drugs in medicated feed and medicated drinking water are largely unknown, as well as the residual concentrations of the drugs after the end of the treatment. Results This study presents a qualitative risk assessment to estimate the magnitude of the risks for reduced homogeneity and stability, and increased residual concentrations of antimicrobial drugs in medicated feed and drinking water on the farm. Risk assessment was done using a questionnaire and farm visits (n = 52), combined with a second questionnaire, and concentrations of amoxicillin and doxycycline measured in medicated feed and water samples, each collected on 10 farms. For medicated feed, the duration of storage in the silo did not show to influence the concentration levels in a consistent trend, while the treatment duration had a low to negligible effect. A moderate to high risk was found caused by human error when preparing the medicated feed on the farm. Purchased medicated feed greatly reduces the risk of human error and drugs remain stable during the duration of treatment, while the risk of residual concentrations after the end of the treatment was estimated to be low to moderate. The feed intake variability was identified as a moderate to high risk factor. For medicated drinking water, the type of dosing pump, age of pre-solution, and human errors during the preparation of the pre-solution present a moderate to high risk on homogeneity and stability. Precipitation of the active substance in the absence of a stirrer in a drinking water tank was shown to be a low to moderate risk factor for residues after treatment. Waterline length had a weak correlation with the concentrations of the antimicrobials, while a moderate to high influence was detected for the water intake by the pigs. Conclusions A considerable variation in drug concentration in both medicated feed and medicated drinking water was detected depending on their preparation. Therefore, it is important to know which factors influence the homogeneity and stability, and the residual concentrations after treatment