The future of bovine TB control

An awareness of the real time required to achieve eradication revealed from local recent data may prevent unrealistic expectations of any initiatives implemented

14 April 2021, at 9:00am

The future direction of bovine TB control has been a hot topic in the veterinary profession in the past years, with the aim of achieving Officially Bovine Tuberculosis Free status for England by 2038. In March the British Cattle Veterinary Association (BCVA) responded to Defra regarding a consultation on proposals to help eradicate the disease in England, specifically views on changes in testing, responsible cattle movement and whether farmers should be rewarded for low-risk cattle-purchasing behaviour (BCVA, 2021).

A fresh Bovine TB Partnership of 17 members is in place, with expertise from the farming industry, veterinary science, conservation and academia. The brief includes setting the strategic direction of the bovine TB disease eradication programme, helping to set standards, monitoring progress and identifying where new approaches might be needed. The members are also charged with assisting Defra ministers and officials to co-design potential new policies and communications. The government has already set out priorities that include a transition to badger vaccination, accelerating work to deliver a deployable cattle vaccine and improving diagnostic testing. Every cattle vet in the country will have views on what has been done in the past and whether people, badgers or organisations should be culled.

In 2000, there were over 106,000 cattle herds in England, Wales and Scotland, and currently there are some 74,000 (Defra, 2021a). The numbers have been fairly stable over the past three years with England having around 49,000 cattle herds, Wales 12,000 and Scotland 13,000. Herds that were not TB free were recorded as 873 in 2000, 3,326 in 2010 and 3,117 in 2020 (at 4 percent of the herds: 3,117/74,053). Veterinary practices will be aware of the location of the herds that are currently under restriction.

Cattle slaughtered for TB in the year ending August 2020 totalled 37,800 (27,810 in England; 9,762 in Wales; and 261 in Scotland; Defra 2021a). The numbers of slaughtered beasts compensated would be of concern for the Treasury and the number of herds under restriction of concern to the farmers. It might be worthwhile for those now deliberating the future to agree on a single measure that indicates progress or not. The sheer scale of the TB statistics available is rather daunting and unlikely to encourage working farmers and their vets to spend time looking for trends to build confidence. The communication part of the brief would seem to be very important moving forward.

The South West of England has traditionally contributed much to the TB facts and figures. In the year to the end of August 2020, there were 14,206 herds (Defra, 2021b), which is a small increase over the previous two years (14,136 in 2018), but the number of herds that were not TB free has fallen from 1,620 in 2018 (as of 31 December 2018) to 1,170 in 2020 (as of 31 August 2020), so matters appear to be moving in the right direction. New herd incidents have also fallen from 1,867 to 1,602. Further probing of the statistics shows that the disease-restricted herds were located in Cornwall (215), Devon (409), Dorset (94), Gloucestershire (115), Somerset (151) and Wiltshire (110). If veterinary practices were to be given the responsibility of reducing the TB incidence within their practice, the volume of work would be manageable and a direction for discussion – for example, the 624 restricted herds in Devon and Cornwall are serviced by 36 TB testing practices.

The delivery of TB testing has been reassessed and from October there are expected to be four managed groups for England and two in Wales. Having worked through the many practical issues with the changes to the testing programme, the Veterinary Delivery Partnership (VDP) has earned its spurs and is able to absorb information from vets in the field and route valuable changes through to government. Looking forward, veterinary surgeons may find that the VDP is able to go beyond the recording results hiccups and place a stronger veterinary clinical element into future developments. It seems to pass under the radar that veterinary advice is delivered during the TB testing process. A vet is likely to be spending several hours on-farm over a couple of days servicing the test and once the pleasantries are dealt with discussions about management for TB take place. This may be partly why the TB Advisory Service has not been taken up as strongly as anticipated.

A fresh approach for reducing the bTB burden could be to concentrate veterinary effort on the dairy herd, with 8,735 in England and Wales in 2019, 2,586 in Northern Ireland and 888 in Scotland (AHDB, 2020). The shires and counties of England and Wales with over 400 milk producers in October 2020 are: Devon (861), Cumbria (688), Somerset (561), Cheshire (469), Lancashire (466), Staffordshire (440), Carmarthenshire (435), Cornwall (431) and North Yorkshire (412). The contribution of dairy herds to the bTB incidence is not recorded in the national statistics, but a veterinary practice would be able to stick red pins in the practice map. Dairy herd management is food and drink to many veterinary practices, with strong relationships in place. If veterinary practices were encouraged to offer a dairy farmer a bespoke control service that incorporates the latest technical developments, a considerable uplift in farmer confidence is possible. Milk monitoring of bulk tanks is an option with the possibility of individual regular cow disease status. The milk findings would supplement current skin and blood tests.

Responses to the survey are likely to include the aspect of infected cows being left in the herd with repeated testing. The skin test is considered an effective approach for most herds, as a herd screen, but the variation in sensitivity on any given day is of concern. Greater confidence in the use of an individual animal test, pre- and post-movement, would be a major step forward. For veterinary practices to identify and support dairy herds that are under bTB restrictions, utilising “all the tools that can be put in the box” would be advantageous. The application of whole genome sequencing to replace genotype testing is due and it is intended that the source of infection will be better identified, whether cattle-to-cattle or from wildlife.

The new partnership will be in a position to consider all developments and activities. Are slaughtered TB bovines likely to be asymptomatic or subclinical? Considerable science will be available to agree whether a bovine that fails the skin test would be expected to be disadvantaged by the disease in the future. If the animal remains healthy, then beef herds of animals being reared for slaughter, within three years of age or so, could be excused routine skin testing. Tissue analysis post-slaughter could provide surveillance, utilising the improved rapid and low-cost tests becoming available.

If the calculations are agreed and 4 percent of the national herd are currently not TB free, then bearing down on the failing herds is a positive way forward. Ten years ago, the figure was also 4 percent (3,326/83,129; Defra, 2021a). If eradication is to be achieved by 2038, then the 3,117 herds currently restricted need to be down to 2,000 within 10 years, with a continuing similar reduction rate thereafter. A practical consideration with a herd that has skin-test failures is that the circumstances leading to the failure are likely to still be influencing the next skin test 60 days later. If that test shows more failures, then a minimum of two further 60-day tests and a six-month negative are needed before the farmer can relax. That is a minimum of a year for the herd to be considered TB free. An awareness of the real time to achieve eradication, revealed from local recent data, may prevent unrealistic expectations of any initiatives.

Cattle veterinary surgeons are aware of the uptake by farmers of the Johne’s control programme. There may be lessons here for bovine TB control. The cattle industry is poised to gain confidence from the new TB Partnership.