Analysis of antibiotic residues in liquid manure and leachate of dairy farms in Northern Germany

The scientific interest in the fate of antibiotic substances in the environment has increased during the past decades. Especially in animal husbandry, the assumed quantity of antibiotics excreted has caused major concerns as the environment can be contaminated by these compounds via different paths. In this study in Northern Germany, manure and leachate samples from dairy farms were analysed in order to verify if this kind of animal husbandry can be a source of antibiotic residues found in the environment. Neither in liquid manure nor in leachate were the analysed antibiotics detected. These results clearly show the minor importance of dairy cows as sources of antibiotic residues in the aquatic environment. To explain this fact, we propose the three following reasons: (i) the amount of antibiotics administered in dairy farming is low compared to pig or poultry production; (ii) manure storage is a useful process to minimize the antibiotic residues as the substances applied to dairy cows are sensitive to degradation processes during that period; (iii) excreted directly on grasslands, the substances degrade very quickly or adsorb to soil and are therefore not present in the leachate.