Milk testing offers the dairy farmer a convenient method of testing for Johne’s disease without the need for blood sampling.
Bulk milk testing is not a recommended screening method for Johne’s disease. Due to the nature of the disease the bulk milk test is not sensitive enough. It is possible to have a high level of Johne’s infection in a herd and test negative on a bulk milk screen. A negative bulk milk Johne’s test does not necessarily mean that your farm is clear of Johne’s disease.
A good indication of the herd prevalence of Johne’s disease can be determined by testing a selected group of 30 cows within the herd. It is best to consider animals for testing against the following criteria (in order of priority):
- Between 3 – 7 years old
- Cows affected by lameness
- Generally depressed animals
- Repeat high SCC or mastitic cows
- Cows demonstrating a drop in milk yield
For those herds undertaking milk recording it is possible to have the appropriate cows automatically selected. Contact your milk recording organisation (MRO) for more information and to arrange this test. It should be noted that culling decisions should not be based on a single milk test – the 30 cow screen is simply a herd level indicator. On receipt of test results from the 30 cow screen, the next step should be a discussion with the vet to determine the biosecurity/containment risks for the farm and to establish an ongoing surveillance strategy.
For herds with no evidence of infection from their initial screening tests a programme of ongoing surveillance is recommended. Periodic targeted 30 cow screens are an excellent method of monitoring your herd status. Quarterly surveillance packages are available through milk recording organisations, contact your MRO for further details.
Individual cow testing
Forms an integral part of many control programmes and can be easily carried out using milk samples collected for normal milk recording. This provides a cost effective method of testing and allows repeated testing without the need for additional handling and bleeding of the cows. Quarterly testing allows a picture of the animals disease status to be established and a risk status assigned to each cow. This risk status shows the likelihood of the cow transmitting the disease and follows the standard traffic light system. This allows management decisions to be made as part of an ongoing control programme.
RED: Very likely to be infected and infectious
AMBER: Likely to be infected but may not be infectious
GREEN: Low risk of being infected