The aim of this longitudinal study was to compare key markers for the two main pathogens associated with post-weaning diarrhoea, namely enterotoxigenic Escherichia coli and rotavirus, to examine any change in frequency and pathogen strain before and after removal of therapeutic zinc oxide (ZnO) supplementation at 2500 ppm from weaner diet. The study also aimed to identify any changes in carriage of antimicrobial resistance genes in herds before and after ZnO withdrawal, because metals such as zinc are associated with the carriage of multiple drug resistance in bacterial populations. We further aimed to compare the gut microflora composition pre- and post-withdrawal of ZnO, in order to identify components that may be associated with disease or with better resilience to diarrhoea. Finally, we aimed to identify management, husbandry and biological factors which may mitigate the impact of ZnO removal from feed on the incidence of post-weaning diarrhoea and poor weight gain, through epidemiological analysis of data from participating farms and from a wider survey of the UK pig industry.
Prior to the start of the current project, in January 2022, the planned implementation of the UK regulatory removal of ZnO supplementation from weaner diet was delayed by two years, from the original date aligned with the European Union withdrawal timetable of June 2022, until a later date in the UK of June 2024. This UK regulatory change to implementation has meant that this priming Phase 1 study has only been able to collect pre-withdrawal samples and a small number of early post-withdrawal samples from recruited herds, because many herds decided to delay the withdrawal of ZnO from their weaner diets until 2024, due to concerns about the impact on piglet health and welfare. Therefore, the original project objectives have been rolled over onto a new, onward Phase 2 project, for which the consortium team have been successful in obtaining further BBSRC funding through a responsive mode grant application. This Phase 2 funding is a three-year consortium award of value £1.1 million across four academic institutions, and with additional financial and in-kind contributions from an industry partner. This new Phase 2 award commenced in March 2024 and will run until February 2027.
To date, twenty-four commercial herds have been recruited to the planned longitudinal survey established during this Phase 1 award, that will progress beyond the end of the award into Phase 2. Field samples and data have been collected from these herds over the past 12 months, with all pre-withdrawal samples collected, and early post-withdrawal samples from one third of herds that withdrew ZnO during 2023. The remaining two-thirds of herds will remove ZnO over the next four months, before the end of June 2024.
Data from the pre-withdrawal samples analysed so far have identified the predominant enterotoxigenic E. coli virulence factors currently circulating in the sampled herds in England, Scotland and Northern Ireland, with the F4 antigen greatest at both sample and herd level in England and Scotland, and F18 dominating in Northern Ireland. All herds yielded weaner samples that were positive for rotavirus A, B and C subtypes, and rotavirus H was not detected. Finally, the presence of integron mobile genetic elements, used as a proxy marker for multiple drug resistance carriage, was widespread in all herds.
A low temperature biobank of the collected faecal samples has been established as a resource for the ongoing project and for future research into pathogens associated with post-weaning diarrhoea, microbiome resilience and transmission of antimicrobial resistance within commercial herds in the UK. Currently we have banked over 1200 samples from a range of life stages and timepoints during the transition to full ZnO removal across the recruited herds. A laboratory information management system has been established to enable optimal curation of the herd samples and data, and to ensure data security.
A producer attitude social survey interview study has been developed, to obtain detailed in-person feedback from producers on the impact of ZnO removal. This is based on a telephone interview questionnaire format, which has been designed, piloted and ethically approved. To date eight interviews with producers from a subset of the recruited study herds have been conducted pre-withdrawal. These interviews have provided detailed insight into the challenges, barriers and attitudes of producers for managing post-weaning diarrhoea in their herds and their concerns regarding the UK wide regulatory removal of ZnO supplementation from weaner diets.
Finally, to gain a wider understanding of the impact of ZnO withdrawal across the whole industry, beyond the herds recruited to the longitudinal study, a UK-wide pig livestock sector online survey has been developed. This survey has been designed, piloted, ethically approved and launched through newsletters and social media sites across a number of national organisations and veterinary practices, targeting pig producers. This online survey is currently ongoing, with an aim to collect responses from over 60 producers in total, and will report outcomes in the next few months.
