Test frequency is at vets discretion
THE MAJORITY of beef and dairy cattle in Great Britain are tested for tuberculosis every four years.
But certain regions, such as the south-west and south Wales, where there is a higher incidence of disease, are tested every one, two or three years depending on the level of infection.
Within any area the district vet officer has the discretion to apply testing more often, depending on the level of risk.
The two-day test is carried out by local veterinary surgeons, who act as MAFF agents. On the first day 0.1ml of avian tuberculin is injected four inches into the neck directly above a 0.1ml interdermal bovine tuberculin injection. Both extracts are sterile. Skin at the injection sites is then folded and calipers used to measure its thickness.
After 72 hours the vet returns and reads the test. This involves measuring the same area with the calipers. When there is no lump, the recording is the same as when first measured. But when there are lumps, the thickness across the lump is measured and the readings between the two injection sites compared. If the difference between the two lumps is 4mm (0.16in)and the bovine lump is bigger than the avian lump there has been a positive reaction.
When the comparative thickness is less than 4mm (0.16in), but the bovine lump is greater than the avian lump, the result is described as an inconclusive.
Sixty days must pass before retesting to allow for the lumps to subside. The injections sensitise animals who, if retested a week after the second test, will record as if a reactor.
Tuberculosis breakdowns in 1994
(*Cornwall, Devon, Somerset, Wilts, Glos, Avon, Dorset). 1995 figures available early summer.