Testing cattle for bovine TB

We must identify and remove infected animals as soon as possible to control this disease. 

Why this is important

In the past, there were human cases of bovine TB, as a result of drinking raw milk. The human population is now largely protected by the pasteurisation of milk and by meat inspection. 

Clinical cases of TB in cattle are now rare, due to TB testing programmes.

Demonstrating freedom from TB in individual herds, in specific regions,  and throughout Wales will:

• save the tax-payer money
• be important in the future trade of live animals and goods
• improve our agricultural reputation.

Find it

We use a skin test in the neck of cattle to identify infected animals. This compares the hypersensitivity reactions to the injection of both bovine and avian tuberculin. Generally  animals that react to the bovine more than the avian tuberculin are considered as skin test reactors. This is a very old test, but is still used worldwide as the main surveillance test for TB control programmes. The test is likely to identify only one ‘false positive’ animal in every 5000 non-infected cattle tested. But, at best it may only identify 80% of infected animals. There is currently no test, or combination of tests, that will:

• identify all cattle infected with TB, and
• identify all non-infected cattle as negative animals

An Interferon-gamma blood test is also used in some herds to help identify other infected animals.

 We test:

• each herd every year
• any animal before it moves off farm, except for: 
  • calves under 42 days of age, or 
  • animals moved to an abattoir, a slaughter gathering or a collection centre, where all animals are being sent to slaughter

We inspect animals at the abattoir to identify any infected with TB, not identified in the testing surveillance programme.

We penalise livestock keepers who do not adhere to our testing regime.

Deal with the source of infection

If we suspect that an animal has TB:

• we isolate it from the herd
• we slaughter the animal, arrange for a post-mortem on it’s carcass and try to culture the organism
• we carry out an epidemiological assessment to identify the origin of infection
• we place movement restrictions on the whole herd
• we arrange for tests in neighbouring herds
• we trace purchased animals and may arrange for further testing in the herd of origin

Stamp it out

If an animal tests positive for TB:

• arrangements are made to value and slaughter it shortly after
• we carry out further testing on the herd at regular time intervals. Testing continues until no reactors are identified, usually after 2 consecutive test
• we identify animals moved out of the herd during the risk period, before disease was identified. We carry out further testing on them

If we fail to identify and remove infected cattle, they can act as ticking time-bombs in the herd for many years. Sometimes infecting other animals in the herd in a progressive insidious way. Sometimes leading to ‘explosive outbreaks of disease.

Where we continue to identify reactor animals in herd 18 months after the breakdown started:

• we ask the Animal and Plant Health agency (APHA) to look at the case
• APHA will work with the keeper and their private vet  to identify the causes
• they will draw up a targeted action plan to control them.

Our aim is to support these herds to become TB free.

Stop it from coming back

Movement restrictions are lifted from herds which have satisfied the breakdown testing regime.

Herds which have been recently released from restrictions are more likely to suffer a TB breakdown. About 30% of breakdowns recur with 2 years of restrictions being lifted.

The causes of recurrence include:

• introduction of new infection from wildlife. There are practical measures keepers can adopt to prevent  contact between cattle and badgers in high risk areas of the farm
• introduction of new infection by purchasing an infected animal. Keepers look for an animal, which suits their requirements at the right price, but ignore the risk of introducing TB into their herd.
• infected animals remain in the herd despite our breakdown testing regime. Long-term breakdowns must meet further testing measures. This minimises the risk of infected animals remaining in the herd at the end of a breakdown.