Bovine TB: Research project summary
Project SE3026: Bovine TB in restocked herds: Risk factors and dynamics
Project duration: 3 years 10 months
The aim of this research was to identify risk factors associated with the introduction and transmission of bovine tuberculosis (bTB) in restocked herds following the foot and mouth disease (FMD) epidemic in 2001.
The key findings of this research were:
- Approximately 50% (75/148) of the farms in the longitudinal cohort study on restocked and non-restocked herds within the Randomised Badger Culling Trial area had a herd breakdown (HBD) during the study. Whilst restocked herds appeared to be at reduced risk immediately after FMD, the two groups had similar bTB incidence during the whole study.
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The significant associations between HBD and farm management practices were: purchasing steers, purchasing cattle from markets (versus private sales), increasing herd size, storage of manure in enclosed places compared with storing in the open or spreading immediately and not feeding supplementary minerals and vitamins.
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Approximately 1,000 out of 55,000 cattle that were tested on the farms between 2001 and 2004 were reactors. The strongest associated risk for being a reactor was the number of reactors cattle were exposed to before the test. Bovine TB history of the farm and herd size were also associated with reactors.
- Approximately 6% (177/2941) of the newly formed cattle herds in the retrospective cohort study of restocked farms throughout Great Britain broke down at their first bTB test after restocking.
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The risks of HBD in restocked herds were associated with herd size, the history of bTB on the restocked farm and with purchase of cattle from source farms with a perceived high risk of bTB infection, indicated by a greater than biennial frequency of testing for bTB. The risk associated with history of HBD on the farm reduced the greater the time since the last HBD. If the last HBD was five years previously the risk was not increased.
- Considering the GB cattle population as a whole, bTB testing data (VetNet) combined with cattle movement data (British Cattle Movement Scheme - BCMS) showed that in 3 randomly selected cohorts 72-84% of animals died prior to being tested for bTB.
- Mathematical models indicate that the qualitative patterns of changes in bTB incidence can be explained by the dynamic consequences of changing testing interval.
- Mathematical models indicate that the distribution of reactors within herds may be explained by a delay in cattle becoming infectious so that some reactors are infectious and others are not.
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Page last modified:
July 7, 2008