Sophie Hedges: Antimicrobial residues in meat from chickens in Northeast Vietnam: analytical validation and pilot study for sampling optimisation

To evaluate the risk in Vietnam, we validated an analytical method to detect antimicrobial residues from chicken meat samples and carried out a pilot cross-sectional study to identify optimal sampling strategies. A total of 45 raw meat samples were collected from 4 markets, 1 slaughterhouse and 4 farms (5 per site) in Northern Vietnam, between March and April 2021. Farmers were asked about antimicrobials used during sampled production cycles (5 chickens sampled per batch). Samples were analysed using liquid chromatography-tandem mass spectrometry for the presence of 68 antimicrobials at a pre-defined validation concentration. 7 compounds were identified from 4 classes (tetracyclines, sulphonamides, macrolides, and fluoroquinolones). In markets, where the source of sampled chickens was unknown, a diverse pool of residual antimicrobials was detected in 20% (4/20) of the meat samples. No residues were detected in samples from the slaughterhouse. No residues were detected in chickens from the one farm that reported using antimicrobials, whereas sulfadimethoxine, doxycycline and tilmicosin residues were identified from the other 3 farms reporting no antimicrobial use. The probability of detecting antimicrobial residues present in a flock based on sampling a single chicken was estimated at 0.93 (highest density interval 0.735–0.997). The preliminary results suggest a disparity between farmers’ reports on antimicrobial drug use and actual usage, and that the analysis of a single sample per farm has a high probability of detecting antimicrobial residues, if present.

1 Introduction

An increase in the global demand for protein from animal sources has been paralleled by the intensification of livestock production, particularly within the poultry sector. This has resulted in an increased use of antimicrobial drugs (AMDs) for the prevention (prophylaxis) and (therapeutic) treatment of disease, and, on occasions, for use as growth promoters (Page and Gautier 2012; Kim et al. 2013; Chattopadhyay 2014; Carrique-Mas et al. 2015; Nhung et al. 2016). Antimicrobial drug use in livestock poses a threat to disease control globally and causes concerns for human, animal, and environmental health due to its contribution to antimicrobial resistance (AMR) (Donoghue 2003). The issues surrounding AMR and AMD usage in livestock have been highlighted in recent strategy reports including a Global Action Plan by the WHO that lists certain AMDs (including gentamycin, erythromycin, and colistin) as critical for human health and calls for their restricted use in livestock and agriculture (World Health Organization 2015; Collignon et al. 2016; World Organisation for Animal Health 2016). In poultry, antimicrobial drugs are commonly administered at high levels around the world with different approaches towards monitoring AMD use and evaluation of the prevalence of resistant micro-organisms (Roth et al. 2019). In Vietnam, systems of poultry production frequently differ from those of high-income countries. Around 90% of Vietnamese households keep poultry, of which the production contributes to 19% of households’ income (Desvaux et al. 2008). AMDs are administered to poultry flocks in Vietnam primarily via feed (Van Cuong et al. 2016), with a recent study highlighting the wide range of antimicrobial classes administered within a flock (Nhung et al. 2016). These commonly reported AMDs include penicillins, fluoroquinolones, tetracyclines, aminoglycosides, macrolides, polymyxins, trimethoprim, and amphenicols. The use of antimicrobials as growth promoters has been prohibited in Vietnam since the beginning of 2018 (Ministry of Agriculture and Rural Development in Vietnam 2016).

To ensure the safety of poultry products, maximum residue limits (MRL) are defined as the maximum levels of antimicrobial residues within meat samples that are deemed safe for human consumption. In Europe, MRLs for allowed substances are enforced by Commission Regulation (EU) No 37/2010 (Commission Regulation (EU) 2009). The Codex Committee on Residues of Veterinary Drugs in Foods (CCRVDF) determines MRLs, together with the FAO/WHO Joint Expert Committee on Food Additives (JECFA) which evaluates and recommends levels of Acceptable Daily Intake (Lees et al. 2021). Typically, these levels can be met by adhering to the source-specific withdrawal periods (Landoni and Albarellos 2015), although rules may differ from country to country. In Vietnam, the list of products with MRLs includes fewer medicines than in the EU and the MRL sometimes differs for the same compound between regulators (Ministry of Health in Vietnam 2013). Progressive and consistent implementation of the residue monitoring scheme for the internal market is desirable to ensure consumer safety.

The UKRI GCRF One Health Poultry Hub (OHPH) is an international interdisciplinary research project established in 2019 that evaluates zoonotic health risks associated with the intensification of poultry production. Pilot studies were necessary to optimise the design of larger-scale field studies that aim to gather data on poultry husbandry practices across participating study sites in Bangladesh, India, and Vietnam.

The objectives of this pilot study were to: (1) transfer the multianalyte liquid chromatography-mass spectrometry method for the detection of AMD residues in chicken meat from the EU reference laboratory (ANSES, France) into the analytical laboratory at the Nanyang Technical University, Singapore, (2) assess the types of AMD residues detected in meat samples from farms, markets, and slaughterhouses in Vietnam, and (3) to determine the optimal number of chicken carcasses to sample on a farm to detect antimicrobial residues present in the farmed chickens.

2 Material and methods

Ethical approvals were obtained from the National Institute of Veterinary Research (NIVR) (020-433/DD-YTCC) and the Royal Veterinary College (RVC) Ethics and Welfare Committee (URN: 2020 1983-3).

2.1 Sample collection

The pilot study ran between March and April 2021 as part of a larger project that involved sampling chickens on markets, slaughterhouses, and their supplying farms in Northern Vietnam. The study was conducted in Bâc Giang province, Vietnam, with 1 additional farm site located in Thái Nguyên province (Fig. 1). The Thái Nguyên site raised exotic white broiler breeds (e.g., Ross, Cobb, Arbor Acres). The other 3 farm sites in Bâc Giang raised hybrid coloured broiler chickens, which are the crossbred progeny of a mating between indigenous males (e.g., Ri, Choi, Ho, Dong Tao) and exotic hens (e.g., Luong Phuong breed from China). The size of the farms varied, with the smallest having 400–500 chickens (Farm 3) and the largest having 4000–5000 chickens (Farm 2).

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