May 2026 – A good time of year to complete your WHT

Now is a great time to carry out your Whole Herd Test (WHT) for Johne’s disease as it gives time to interpret results and plan for the future. WHTs are carried out by either blood or milk sampling all eligible animals in a herd and testing by ELISA. In terms of Johne’s testing, eligible animals are those aged two years and above on the date sampling commences (animals required to be tested include both male and female animals plus any scheduled for culling). One useful feature on your ICBF Johne’s web page is the ‘WHT Eligible’ option which allows you to input the planned sampling date and generate a list of animals eligible for testing on that date.

One practical consideration is to complete your WHT as early in the lactation cycle as possible and avoid milk testing in late lactation (usually October to November). At this time of year an increased number of milk samples return positive and inconclusive results, requiring faecal sampling to further investigate their status in herds where infection has not previously been confirmed.

Another practical consideration when planning your WHT is your TB test date, as it is recommended not to sample for a WHT for the subsequent 90 days due to possible false positive results which will again require further testing to resolve. It is also important to remember that any Johne’s milk sample tests carried out within seven days of an animal calving and which return a positive or inconclusive result must be repeated.

Once your WHT is completed the results are sent to your Approved Veterinary Practitioner (AVP) or milk recording organisation that sampled the animals, and they are also available to you and your AVP on ICBF. Remember that there may be other animals on the farm to be sampled, not just the milking cows which are sampled at milk recording. These other cattle are usually tested by blood sampling at a ‘sweeper’ test carried out by the AVP. The aim is to get this ‘sweeper’ test carried out as soon as possible after the main test; the programme advises it be completed within 30 days after the main test.

So remember the main points for arranging your Johne’s Whole Herd Test

• If you have not done so contact your Milk Recorder and organise a Johne’s test as soon as possible. If you do not milk record, contact your vet and organise your Johne’s test through blood sampling.
• Always be aware of the timing of your TB test in relation to Johne’s testing. If you are on short interval TB testing which could potentially impact on your Johne’s testing schedule, contact your AVP and they will be able to offer you best advice.
• Make a note of all eligible animals in your herd and be ready to complete a ‘sweeper’ test of any animals missed at the WHT, within 30 days is best.
• When the test is completed, and results produced speak directly with your AVP who is best placed to give your herd tailored advice and arrange any follow up testing.