Wednesday, January 12, 2005

The Impact of Badger removal on the control of tuberculosis in Cattle herds in Ireland

We entitled this post with the same wording as the result of the 4 area study, which was published January 5th.2005. For anyone who wants the full transcript, this can be obtained from .

The impact briefly was that procative culling of badgers in the 4 area study saw a " 60 - 96 percent decrease in the rate at which herds were becoming subject of a confirmed restriction" compared with the Reference area where only Reactive culling took place.

In the Republic of Ireland, (like the UK) m.bovis is endemic in the badger population. A growing recognition of the role of wildlife as reservoirs of tuberculosis led to the setting up of field trials to determine the role of badgers. The UK has done such excercises to which we have referred in Thornbury, Steeple Leaze and Hartland with a larger 'trial' being conducted at East Offaly (R of I) in the mid 1990's. The UK is still operating the Krebs trial.

East Offaly was critised for allegedly causing the enforced 'migration' of badgers through the buffer areas. The 4 area study tried to avoid this, and followed the impact of badger removal in a wider range of environments, the four areas chosen being different geographically and with different types of farms.

We will compare the 4 area study with what we have learnt of John Bourne's Krebs trials.

* Where natural barriers were absent (rivers, mountain ranges and sea) , buffer areas of up to 6 km were created.
Krebs. Circles on a map, with boundaries which 'altered' after commencement of trial, and buffers of 1 - 1.5 km.

*Each area managed by a single team (both pro active removal and reference) and supervised by a single DVO (Divisional Veterinary Office)
Krebbs. Wildlife team of 133, moved from site to site (10 triplets of 3 areas each) and spent up to 5 hours per day each on the motorway. Local SVS involvement excluded. Designed and run by ISG.

*Study herds comprised all herds within the reference areas.
Krebs. Excluded herds already under Tb restriction at start of the 'trial', leaving 'hotspots' within the trial areas which could not qualify for clearance and did not qualify for data capture.

*Participation voluntary. Only 19 ha in Cork was refused access to survey. Badger Removal was refused at 13 surveyed setts. (0.42 percent of total) located at Cork (5 setts) Donegal (5 setts) and Kilkenny (3 setts).

Krebs. 50 percent of one Cornish triplet 'out of bounds', with many other areas within the triplets excluded.

*Method of capture wire snares, followed by shooting. Removals carried out 2 or 3 times a year, repeated if evidence of badger activity was detected.
Krebs. Traps, 57 percent of which suffered 'interference' and 12 percent disappeared. Of target badger population, 80 percent was the best which could be expected, and as low as 30 percent recorded.
Removal once a year (maybe). In some triplets this stetched to once in 3 years in both Reactive and Proactive. In some Reactive areas, wildlife teams did not arrive at all.

*Reactive culling in reference areas was to a more stringent protocol than that routine used throughout the rest of Ireland. Removal was triggered if a herd suffered 4 or more reactors to the skin test whereas normal procedure in the remainder of the country triggered removal if 2 or more reactors are found and the source 'reasonably attributed to badgers'. A non removal 'control' was not undertaken as it was thought this might encourage illegal removal of badgers within the refrence area.
Krebs. Reactive culling suspended October 2003. Trial has 'control' areas where no culling- survey only took place. No badger removal at all in UK after 1997 in response to cattle tb - and £1 million from the Political Animal Lobby.

*In a recent paper Donelly et al (2003) anticipated the findings of the 4 area study, reporting an increase of tuberculosis in cattle in UK trial, following' reactive ' culling. They speculated that this effect was associated with 'perturbation' or disruption of badgers following small scale removal and would over-estimate the effectiveness of widespread reactive culling The 4 area study found no evidence to support this.
Krebbs. Stopped Reactive culling Oct 2003. Prior to that some farms in reactive areas had not been visited at all, and some had endured 3+ years (and up to 18 sixty day herd tests, and 150 dead cattle ) between 'reactions'. Many farmers withdrew from trial.

*The 4 county study over 5 years confirmed that the herd restrictions in the proactive removal areas were significantly lower than the matched reference areas. (up to 96 percent lower) It is reasonable to attribute this effect specifically to proactive badger removal.
Krebbs. To be continued?

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