Risks of medicating cattle ahead of scheduled TB tests

Almost half of all animals slaughtered on farm have been medicated and are still within the medicine withdrawal period at the time they need to be removed for TB control purposes. The withdrawal period is the duration between administering the final dose of veterinary medicine to an animal and allowing the animal or its food products into the food chain. This is set by regulatory authorities. It ensures that the food does not contain medication levels beyond the maximum residue limit.

The slaughter of an animal on farm is:

• a harrowing experience for the owner to witness, and
• a waste of a carcase which otherwise would be fit for human consumption 

It is not possible to avoid on farm slaughter completely. But there are practical precautions you can take to reduce the number of occasions when this is necessary. 

Medications may interfere with the accuracy of the TB test, as agents may temporarily affect the animal’s immune system and influence the result. Medicated cattle may have to be slaughtered on farm or cause a delay in the removal of infected animals. This can prolong TB problems in your herd and the duration of the restriction. 

So, we advise you to avoid applying routine, non-urgent treatments if the medicine withdrawal period will not have expired in advance of the TB test. Veterinary advice is that you should only give routine veterinary medicines to animals once they have tested clear in any planned TB test. These routine medicines include parasite control or vaccines.

NB. You must give urgent treatment if the welfare of the animal would be compromised without medication.

In Wales, all Officially Tuberculosis Free (OTF) herds must be routinely tested annually. Herds in the Intensive Action Area are tested every 6 months. Herd owners are aware when the tests are due. They generally have a 60-day testing window. They receive a test notification letter from APHA 2 months ahead of the start of the testing window. Herd owners must arrange for their veterinary practice to complete the test during the testing window. This should allow the owner enough time to: 

• apply most routine treatments, and 
• ensure the withdrawal period will have expired before the start of the TB test

We encourage you to:

• discuss the timing of treatments and associated withdrawal periods with your veterinary practice 
• avoid the withdrawal period conflicting with the scheduled TB test