About bovine TB
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This dairy herd situated in the south of Worcestershire is in a TB endemic area. This herd’s TB history dates back to 1997 when it had its first skin test reactor with visible lesions of TB and a positive culture result. Since then TB has been a constant threat with major breakdowns occurring continuously since 2004.
The current farmer took over the business from his father and he has realised that under the current economic climate dairy herds would only survive by modernising, being more effective and professionalised with increased milk production. TB had always been an impeding factor to materialise his plans and in fact he had to stop rearing his own heifers in order to minimise the impact of TB in the herd.
The last major breakdown lasted for nearly six years. During this time over 250 cows were taken as reactors to the skin test. The herd size was around 250 animals in total at the time, so the implications for farm viability were huge.
A large proportion of reactors showed visible lesions at post-mortem examination and there were clear indications that wildlife was playing an important role in the maintenance of the TB cycle in this herd.
This herd was included in the Enhanced Management of Persistent Breakdown (EMPB) herd’s project at an early stage of the process in 2014. EMPBs are those TB breakdowns that have lasted over 18 months and APHA allocates extra resources to undertake further investigations and more sensitive diagnostic (blood) testing if required. It was clear from the beginning that a problem of this scale could not be solved unless APHA and the farmer worked closely in collaboration.
In order to identify the root of the problems APHA worked with the farmer and analysed relevant epidemiological data. This was followed by a farm visit and frequent communication between the farmer and APHA. Together with the wildlife issues, the available data suggested that skin testing on its own was not achieving its objective and infected animals were being left behind. The occurrence of slaughterhouse cases (i.e. negative-testing cattle presenting with lesions of TB in their organs at routine slaughter) was an important clue and this was clear when animal-level data was closely checked.
A number of measures directed towards tackling the problems identified were discussed and implemented. These included conducting a wildlife survey on the farm by APHA ecologists. This survey identified intense badger activity around the farm, although no badgers were seen accessing the cattle buildings or feed stores during the study. This could have been due to the season during which the survey was conducted, since the presence of badgers in the farm yard had been previously reported by the farmer.
Movement-actioned cameras were positioned strategically by APHA field ecologists to capture wildlife activity within the farm yard.
Detailed map of the farm produced by APHA field ecologists showing areas of badger activity.
Electric fence surrounding the whole farm yard.
The farmer was conscious of the role played by wildlife and that in order to break the TB cycle strong biosecurity measures would have to be implemented. The wildlife survey helped in directing these measures to the weakest area of the farm. Amongst the most significant measures introduced was changing husbandry methods and limiting grazing to only dry cows at specific fields and eventually stop outside grazing. The cattle buildings and feed stores were surrounded by badger-proof electric fencing.
Other measures were implemented in order to break other possible routes of infection, including discontinuing the feeding of unpasteurised pooled milk to calves. This was important as transmission of TB through infected milk fed in this manner can result in infection of large numbers of calves.
APHA and the farmer also agreed to use interferon-gamma blood testing in parallel with skin testing in order to increase test sensitivity. The interferon-gamma test identified additional reactors that had not been detected by the skin test and a large proportion of those animals showed TB lesions at post-mortem. As expected, this test also identified a small number of positive animals with no visible lesions, a proportion of which would have been in the early stage of infection. Early identification and removal of those animals reduced their potential to spread the disease within the herd. Following implementation of the enhanced biosecurity measures and the interferon-gamma test there was a dramatic reduction in the number of skin test reactors found subsequently. It is considered that the enhanced biosecurity measures reduced further introduction of infection into the herd and the supplementary blood test helped to remove previously undetected infected animals within the herd.
Following four further short interval (60-day) skin herd tests, APHA finally restored the Officially Tuberculosis Free (OTF) status of this herd after 3 and a half uninterrupted years of movement restrictions.
A further slaughterhouse case in an old cull cow occurred shortly after the herd restrictions had been lifted, but this incident was resolved without disclosing any further reactors in three tests.
Being free of TB has allowed this herd to nearly double in numbers and a new cattle housing building and parlour have been built within the electrified cattle enclosure.
New cattle shed with capacity for up to 500 dairy cows
New parlour with capacity for 40 cows