Future Risk of Bovine Tuberculosis (Mycobacterium bovis) Breakdown in Cattle Herds 2013–2018: A Dominance Analysis Approach

Abstract

Bovine tuberculosis (bTB) remains a significant endemic pathogen of cattle herds, despite multi-decadal control programmes being in place in several countries. Understanding the risks of future bTB breakdown (BD) and the associated characteristics of herds and index breakdowns could help inform risk categorisation. Such risk categories could then contribute to tailored management and policies. Here, we estimated the future risk of herd BD for the cohort of herds that were derestricted during 2013 in Ireland using multivariable logit regression models, with a dominance analysis approach. One third of herds that were derestricted in 2013 experienced a breakdown during the follow-up five year period (1469/4459; 33%). BD length was a significant predictor of future risk, primarily driven by long BDs > 230 days relative to short BDs < 130 days (OR 95%CI: 1.157–1.851), as was having had a previous BD (OR 95%CI: 1.012–1.366). Herd-size was the dominant predictor of future risk (accounted for 46% of predicted variance), suggesting significant increase in risk of future breakdown with increasing (log) herd-size (OR 95%CI: 1.378–1.609). There was significant spatial variation in future risk across counties, and it was the second most dominant predictor of future risk (25% of predicted variance). The size of index breakdowns was not a strong predictor of future risk over a 5-year period. These findings can inform a risk-based policy development.

Engaging With Farmers to Explore Correlates of Bovine Tuberculosis Risk in an Internationally Important Heritage Landscape: The Burren, in the West of Ireland

“…The size of cattle herds has consistently been a risk factor for bTB breakdowns in Ireland and elsewhere when using large national-scale datasets [e.g., (15,16,28,29)], and is therefore unsurprising that a significant relationship was found in the present study. Herds >100 animals, which in the present study represent very large herds, had 19 times higher odds of recent breakdown relative to herds of <30 animals.…”

“…Where a farmer selected two options for herd type, only one was used in the model. The response was always taken as the option with the subjective higher bTB risk, given previous research from Ireland [e.g., (2,(15)(16)(17)]. Explicitly, if a farmer picked two different herd types (i.e., a mixed herd), one including a dairy type herd, then that herd was given the indication of "dairy".…”

Trends and factors associated with dairy calf early slaughter in Ireland, 2018–2022

“…However, only a modest proportion of herd-years were coinciding with bTB breakdowns (22% of calves in the dataset were born in a herd during a year with a TB restriction). Furthermore, there is a strong relationship between herd size and bTB risk in Ireland [e.g., ( 37 )], therefore establishing the causative relationship between bTB breakdowns and slaughter rates is not straightforward.…”

What is the scope for existing (including recently developed) diagnostic methods to detect infected cattle which are not currently detected by the existing programme?

“…c) Residual infection poses a future risk to in-contact animals. Many Irish studies have identified herd TB history as a key risk factor for TB presence within a herd [80][81][82][83][84][85][86][87][88][89]. Animals moving following derestriction were 1.91 times more likely to test positive in the following 2 years compared with animals that moved from herds without such a history [90].…”