Temporal and seasonal trends of bovine tuberculosis in Irish cattle (2008-2024)

Background Bovine tuberculosis (bTB) has substantial impacts on the Irish cattle industry. Between 2016 and 2024, its burden increased in Irish cattle. As an initial step towards understanding drivers of this increase, we explore long-term trends in measures of bTB burden and cattle demographics. Methods Using data from 2008-2024, we describe changes in cattle management and demographics over time, as well as measures of bTB burden at herd- and animal-level. A negative binomial regression model was implemented to explore the association between year and herd-type on the count of bTB cases. Results Between 2008 and 2024, dairy herd numbers remained stable (~12% of all herds), but they expanded significantly in herd-size (median increased from 119 to 172) with the proportion of national cattle in dairy herds increasing from 23% to 34%. The proportion of bTB cases from dairy farms doubled. In 2024, 51% of all individual bTB cases were from dairy herds compared to 26% in 2008. Limitations Although there is known to be strong spatial heterogeneity, this analysis focuses solely on national trends. Conclusions This study serves as a core reference point for programme managers, policy makers and those undertaking modelling analysis to better understand bTB epidemiology.