After administration to livestock, a large fraction of antibiotics are excreted unchanged via excreta and can be transferred to agricultural land. For effective risk assessment a critical factor is to determine which antibiotics can be expected in the different environmental compartments. After excretion, the first relevant compartment is manure storage. In the current study, the fate of a broad scope of antibiotics (n = 46) during manure storage of different livestock animals (calves, pigs, broilers) was investigated. Manure samples were fortified with antibiotics and incubated during 24 days. Analysis was carried out by LC-MS. The dissipation of the antibiotics was modelled based on the recommendations of FOCUS working group. Sulphonamides relatively quickly dissipate in all manure types, with a DT90 of in general between 0.2 and 30 days. Tetracyclines (DT90 up to 422 days), quinolones (DT90 100-5800 days), macrolides (DT90 18-1000 days), lincosamides (DT90 135-1400 days) and pleuromutilins (DT90 of 49-1100 days) are in general much more persistent, but rates depend on the manure type. Specifically lincomycin, pirlimycin, tiamulin and most quinolones are very persistent in manure with more than 10% of the native compound remaining after a year in most manure types. For all compounds tested in the sub-set, except the macrolides, the dissipation was an abiotic process. Based on the persistence and current frequency of use, oxytetracycline, doxycycline, flumequine and tilmicosin can be expected to end up in environmental compartments. Ecotoxicological data should be used to further prioritize these compounds.

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In the combat against bacterial resistance, there is a clear need to check the use of antibiotics in animal husbandry, including poultry breeding. The use of chicken feathers as a tool for the detection of use of antibiotics was investigated. An extraction method for the analysis of oxytetracycline (OTC) from feathers was developed and was tested by using incurred feathers obtained from a controlled animal treatment study. The use of McIlvain-ethylenediaminetetraacetic acid buffer only in combination with acetone gave the highest extraction yield, indicating the need of an organic solvent for feather extraction. By using the developed method, it was found that after a withdrawal time, the OTC concentration in feathers is in the mg kg⁻¹ range, far higher than that in muscle and liver tissue. Based on the analysis of individual segments of feathers from OTC-treated chicken, evidence was found supporting the hypothesis of secretion of antibiotics through the uropygial gland and external spread over feathers by grooming behaviour. It was also found that part of the administered OTC is built into the feather rachis. Finally, we provide the first evidence that the analysis of individual segments of the rachis can be used as a tool to discriminate among different treatment strategies, for example, therapeutic versus subtherapeutic. As a result, we concluded that the analysis of feathers is an extremely valuable tool in residue analysis of antibiotics.

In The Netherlands, all antibiotic treatments should be registered at the farm and in a central database. To enforce correct antibiotic use and registration, and to enforce prudent use of antibiotics, there is a need for methods that are able to detect antibiotic treatments. Ideally, such a method is able to detect antibiotic applications during the entire lifespan of an animal, including treatments administered during the first days of the animals’ lives. Monitoring tissue, as is common practice, only provides a limited window of opportunity, as residue levels in tissue soon drop below measurable quantities. The analysis of feathers proves to be a promising tool in this respect. Furthermore, a qualitative confirmatory method was developed for the analyses of six major groups of antibiotics in ground chicken feathers, aiming for a detection limit as low as reasonably possible. The method was validated according to Commission Decision 2002/657/EC. All compounds comply with the criteria and, as a matter of fact, 58% of the compounds could also be quantified according to regulations. Additionally, we demonstrated that a less laborious method, in which whole feathers were analyzed, proved successful in the detection of applied antibiotics. Most compounds could be detected at levels of 2 μg kg−1 or below with the exception of sulfachloropyridazine, tylosin, and tylvalosin. This demonstrates the effectiveness of feather analysis to detect antibiotic use to allow effective enforcement of antibiotic use and prevent the illegal, off-label, and nonregistered use of antibiotics.

Jacqueline Steenbergen-Biesterbos (NVWA) Contents Summary 1 Introduction 2 Materials and Methods 2.1 Approach 2.2 Prioritising antibiotics 2.3 Prioritising antiparasitics 2.3.1 Unauthorised antiparasitics 2.3.2 Authorised antiparasitics 2.4 Prioritising carbamates 2.4.1 Unauthorised carbamates 2.4.2 Authorised carbamates 2.5 Prioritising NSAIDs 2.5.1 Unauthorised NSAIDs 2.5.2 Authorised NSAIDs 2.6 Matrix for analysis (of residues in animals) 3 Results 3.1 Antibiotics 3.1.1 Matrix for analysis 3.2 Antiparasitic agents 3.2.1 Prioritisation of unauthorised antiparasitics using decision tree I 3.2.2 Prioritisation of authorised antiparasitics using decision tree III 3.2.3 Matrix for analysis 3.3 Carbamates 3.3.1 Prioritisation of unauthorised carbamates using decision tree I 3.3.2 Prioritisation of authorised carbamates using decision tree II 3.3.3 Matrix for analysis 3.4 NSAIDs 3.4.1 Prioritisation of unauthorised NSAIDs using decision tree I 3.4.2 Prioritisation of authorised NSAIDs using decision tree III 3.4.3 Matrix for analysis 4 Discussion 4.1 Discussion on antibiotics 4.2 Discussion on antiparasitics 4.3 Discussion on carbamates 4.4 Discussion on NSAIDs 4.5 Discussion on the matrix 5 Conclusions and recommendations Acknowledgements References Prioritisation of antibiotics using decision tree III Prioritisation of unauthorised antiparasitics using decision tree I for animal products in general Prioritisation of authorised antiparasitics using decision tree III Prioritisation of unauthorised carbamates using decision tree I Prioritisation of unauthorised NSAIDs using decision tree I Prioritisation of authorised NSAIDs using decision tree III List of substances essential for treatment of equidae and substances bringing added clinical benefit according to EU 122/2013 WFSR report 2020.007 | 5 Summary Regulation (EU) 2017/625 prescribes that monitoring of residues in animal products should be performed on a risk basis. However, the regulation does not indicate how such risk-based monitoring should be established. Therefore, the Office for Risk Assessment & Research of the Netherlands Food and Consumer Product Safety Authority (NVWA-BuRO) asked Wageningen Food Safety Research (WFSR) to develop an approach that allows for prioritising substances for monitoring. As a result, three decision trees have been established previously: I. Prohibited substances; II. Natural substances, contaminants and residues of pesticides and III. Authorised active ingredients of veterinary medicines and feed additives. The decision trees have been applied to bovine, porcine and poultry products in a previous project. The aim of the current project was to prioritise antibiotics, antiparasitics, carbamates and NSAIDs in horse, goat and sheep products and in (cow's) milk. The same list of substances as evaluated previously were run through the appropriate decision trees for the specified animal species. In total, 68 authorised antibiotics, 32 authorised antiparasitics, 4 authorised carbamates and 13 authorised NSAIDs were prioritised using d...