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Bovine TB and the “whoomph” effect

If bovine TB testing was reduced today, would the incidence of the disease suddenly increase?

24 June 2018, at 2:43pm

Two experienced cattle vets were discussing the testing of cattle for bovine TB. One noted that it appeared that the incidence of bovine TB went “whoomph” due to the lack of testing during the 2001 foot and mouth outbreak. The implication is that if testing were to be reduced now, incidences of the disease would increase considerably. 

With all that has gone on with successive administrations over the years, there have been many changes and no one doubts that the UK has a serious issue with bovine TB, but it seems worthwhile to consider the “whoomph” effect. 

Analysing 20 years of data 

The Defra-published dataset includes the testing records up to the end of January 2018 and this is dubbed the “latest official statistics”. Detailed notes accompany the dataset, which is available to download from the Defra website, making it easier to interpret. 

The first point of note is that the number of cattle herds within England, Wales and Scotland has fallen over the

The first point of note is that the number of cattle herds within England, Wales and Scotland has fallen over the past 20 years by 50,000 herds and now stands at just over 75,000

past 20 years by 50,000 herds and now stands at just over 75,000. During the five years up to and including 2000, the number of herds fell by 19,000; the herds that were not TB free doubled, with just under 3 million animals tested. The number of animals slaughtered doubled over the five years to 8,500 and the number of herds with movement restrictions also doubled to around 1,000. 

So, prior to the outbreak of foot and mouth disease, it appears reasonable to say that the incidence of bovine TB was increasing. 

Looking at the next five years of data to 2005, the number of herds reduced by a further 13,000; the herds that were not TB free almost trebled; the number of animals tested increased to a little under 5 million; the new herd incidents doubled; the number of animals slaughtered rose to nearly 30,000; and over 5,000 herds were under movement restrictions. This is probably suggestive of the “whoomph”. By this time, most of the animals that were not tested in 2001 were probably dead. 

By 2010, the national herd had reduced by a further 8,500; the number of herds that were not TB free increased by a thousand; testing increased by another 2.5 million animals; new herd incidents went up by 1,000 herds; animals slaughtered increased to over 32,000; and over 6,000 farms were under movement restrictions. 

It seems fair to say that nine years after the lack of testing in 2001, bovine TB was continuing to increase. During that time, there was a fourfold increase in slaughtering and a major increase in testing numbers, on fewer herds. 

Jumping forward to 2015, the situation is similar to the situation today. During the five years from 2010 to 2015, there was a loss of another 7,000 herds; an increase in herds not TB free of nearly 400; an increase in testing to

TABLE 1 The latest data published by Defra for 12 months up to the end of January 2018
TABLE 1 The latest data published by Defra for 12 months up to the end of January 2018

9.5 million beasts; a small increase in new herd incidents; a rise in animals slaughtered to over 36,000; and a fall in the number of farms under movement restrictions of over 1,000 herds. Table 1 shows the figures from the data for 12 months up to the end of January 2018. 

During the past three years, the annual figures have remained roughly the same except for a rise in bovine TB slaughter cases. The overall decline in the national herd appears to have slowed.

One in nine of the 4.5 to 5 million cattle movements in England are tested each year and around 10 percent are found to be positive for bovine TB

The number of UK milking cows remains fairly stable at 1.9 million and similarly with beef cows at 1.6 million. Information from AHDB Dairy shows that the number of dairy herds in England and Wales continues to fall, with 9,314 (England 7,591) reported in May 2018 – a reduction of 118 herds from the year before and a loss of over 2,000 herds since 2010. 

One in nine of the 4.5 to 5 million cattle movements in England are tested each year and around 10 percent are found to be positive for bovine TB. Of the 900,000 or so cattle movements in Wales, around 20 percent are premovement tested with less than 1 percent found to be positive. There are recognised differences in the way that cattle are managed in different areas. The South West has 29 percent of the cattle herds in England but 59 percent of the herds that are not TB free.   

There has been little change in the number of herds that are not TB free since 2015 in the South West and in January 2018, individual counties contributed as follows: Cornwall 366, Devon 728, Dorset 116, Gloucestershire 189 and Somerset 237. The figures for each region and county are available from the Defra website. 

Bovine TB in dairy herds 

Information on bovine TB data for dairy herds does not appear to be available. There is a general analysis that larger herds have more disease, but this doesn’t open up an awareness of the role of the dairy herd in maintaining the levels of bovine TB in the national herd. It is the dairy herds that receive the in-depth attention from veterinary practices and the impact of a new incident on the farm workload is a concern.

Where there has to be repetitive testing, it is difficult for the farmer and the farm vet to maintain standards for other disease control and animal management. At the start of an outbreak, the vet is unable to predict whether more cows will be taken in 60 days, whether the one or two animals slaughtered today will increase to many more over the next year or whether the disease will die out in a few months. 

When the farmer has to adjust to a large number of cattle slaughtered, he cannot be confident that the disease will then decline. Do more slaughtered animals mean less disease to come, or is a greater incidence of slaughter an indication of a longer-term problem? 

There appears to be a valuable project for one of the universities to interrogate the data and analyse the detail of bovine TB and dairy herds. 

The larger cattle veterinary practices may prefer to carry out their own analysis on the data from their clients. Vets increasingly use robust handheld computers on farm for the recording of TB tests. There are discussions ongoing about adapting the programs to accommodate wider interrogation as well as recording. This is happening with other diseases. 

Being able to use mobile phones to interact, or replacing the phone with the computer so that one tool satisfies veterinary requirements, is becoming a possibility. Whatever the tools, the involvement of veterinary practices in working with a dairy client and their dairy and beef neighbours to control bovine TB will go beyond gates, fences and movement security. Recognising local changes would increase confidence that management improvements are having beneficial effects. 

Arguably, a greater local understanding of bovine TB will lead to more effective disease control and initiate a national reduction. The managers of the 25-year eradication plan may consider that there has not been one “whoomph” in 2001, but a series of “whoomphs” over the past 20 years. 

Following a 16-year apprenticeship with Beecham, Richard established a project management and development consultancy and writes regular contributions for the veterinary press.

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