Why do this?
Bovine TB can be passed between cattle therefore infected cattle entering your herd can be a source of infection. Introducing any new animal e.g. purchases (including imported animals) or hire bulls, or re-introducing your own stock to your herd (e.g. following a show or returning unsold from market) can be a potential disease risk.
In recent years, it has been demonstrated that cattle to cattle transmission resulting from movements is one of the main contributors to the spread of TB. For example, around 50% of breakdowns in the Low Risk Area (LRA) are due to purchase of infected cattle. In the High Risk Area (HRA), given that 84% of non-slaughter movements of cattle are to other holdings within the HRA, it must be assumed that movements are also a significant contributor to TB transmission in the HRA.
How to reduce your risk
Ask for TB history information before you buy new cattle
Try to obtain a full TB history of herds from which you purchase cattle so that you can assess the level of risk and take action to manage it. As a minimum, you should ask for:
- Date of the animal’s pre-movement TB test. Not all animals require pre-movement tests, but those that do should have been tested in the 60 days before their sale. Pre-movement TB testing reduces the risk of undetected infected cattle spreading disease.
- Date of the seller’s last routine herd test. Knowing this date may offer additional reassurance if the herd has tested negative for TB recently, or it may prompt you to consider carrying out isolation and post-movement TB testing before introducing the animal into your herd. If the last herd test was some time ago or you are uncertain about the testing history (e.g. if the animal was not bred on the holding from which it is being sold), you should consider isolating the animal and ask your vet to conduct a post-movement TB test.
- Date the herd achieved officially TB free (OTF) status. All animals offered for sale should have tested negative for TB and come from an OTF herd. However, the length of time that the herd of origin has been TB-free can be an indication of the level of TB risk of sourcing cattle from that herd. The longer a herd has been free of TB restrictions, the lower the risk and conversely a herd that has recently come off restrictions is likely to be higher risk.
Post-movement test cattle entering the herd
Infected cattle do not usually show clinical signs of TB and will look healthy. Post-movement testing is another line of defence to detect infected cattle prior to introducing them into your herd, and reduce the risk of them spreading TB to your other cattle.
Post-movement TB testing was introduced in England on 6 April 2016. Herd owners in the LRA of England must arrange and pay for post-movement tests for cattle bought from herds in annual (or more frequent) surveillance testing areas of England and Wales. Post-movement testing is not required for cattle slaughtered within 120 days of arriving in the LRA, or that are moved to a Licensed Finishing Unit (LFU) approved by APHA (unless the cattle have had no pre-movement test).
Post-movement TB tests must be completed between 60 and 120 days after an animal has joined a herd in the LRA. Government-funded TB tests scheduled to take place within the 60-120 day post-movement testing window can be considered valid post-movement tests. If possible, animals should be isolated until the TB test results are known. Tests for TB are not perfect and a negative result does not guarantee that the animal is free from TB. This is because:
- Approximately one in four infected cattle may be missed by the tuberculin skin test
- The tests are more effective at detecting infections when used on a herd basis rather than on individuals or small groups
Therefore, it is worthwhile carrying out post-movement TB testing even if the animals have passed a pre-movement test as it provides another opportunity to pick up any undetected infection or animals infected with M. bovis following the test e.g. during transit.
The limitations of the TB test create a particular risk in relation to bull hire. As bulls may visit several herds each year they pose a high risk of spreading TB and it would be preferable not to use hire bulls at all.
Isolate all higher-risk cattle before they enter the herd
When cattle enter your farm, it is recommended to isolate them from other cattle in the herd to ensure that they are not incubating any disease (not just TB) and to give you time to test them. If you are buying in cattle from a herd of higher TB risk status (based on your assessment of the three factors above), they should always be isolated. The period of isolation should be at least 60 days so that a post-movement TB test can be carried out before introducing them into the herd.
These recommendations apply to all cattle entering the herd, including newly purchased stock, hired bulls, and cattle that are already under your ownership but that return from being away, e.g. from shows, markets and from other premises. The risk is greater for purchased stock and hired bulls than for animals that have been off the farm for a short time. Nevertheless it is important to assume that even short spells off farm can potentially give opportunity for infection to be acquired.
The practicality of isolating cattle will depend upon a number of factors, including the number of animals purchased, their purpose (management stage) within the herd and the availability of suitable isolation facilities. Discuss with your vet what options would be appropriate for isolation on your farm.