Intended and unintended consequences of the ZnO ban from pig diets on antimicrobial resistance, post-weaning diarrhoea and the microbiome.

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Post-weaning diarrhoea (PWD) is the most significant challenge to pig rearing throughout the industry, affecting health, welfare and production. Zinc oxide (ZnO) is added to weaner diet at high levels to control disease, however this practice is now banned in the EU, due to associations with antimicrobial resistance (AMR). In the UK, ZnO will be prohibited by June 2024 and it is expected that PWD, and consequent use of antimicrobials for treatment, will increase.

We will conduct a longitudinal study, re-visiting farms from a pre-ZnO ban survey, to evaluate the impact of the ban on PWD and prevalence of causative pathogens, enterotoxigenic Escherichia coli (ETEC) and rotavirus. We will collect faecal samples from pens, record changes in antibiotic usage and identify any shifts in AMR diversity, following ZnO removal. Genomic analysis using long and short read sequencing will enable tracking of AMR genes and multiple drug resistance, comparing across age groups on farm, with and without ZnO. Associations and putative genetic linkage between ARGs, mobile elements, heavy metals, and biocide resistance will be identified. Through phylogenetic analysis, we will examine whether the ZnO ban results in change to the predominate ETEC circulating clones in the UK.

Alternative strategies are urgently required to manage PWD. By means of a highly-powered trial, we will identify differences in structural and functional microbial communities within the intestine that are associated with ZnO supplementation. Through metagenomic sequencing, we will characterise the local microbiota and identify which consortia are associated with reduced PWD and better growth. Using a novel, culturomics approach, we will isolate beneficial microbes from ZnO-supplemented groups, to identify microbiota-based solutions which may be exploited to enhance resilience during weaning. Findings from this study will be shared with the farming industry and stakeholders through knowledge exchange events.