For information on specific aspects of Johne's disease please click on the relevant links below:
Impact of Johne's disease on cow performance
A number of international studies have been completed in recent years that demonstrate the impact of Johne's disease on cow performance in terms of reduced yield, increased lameness, increased mastitis and increased susceptibility to other diseases. These effects have also been shown to be evident in UK dairy herds. Check on the technical documents available for downloading for more information. An example of such studies is: Hanks, J.D., Taylor, N.M. and Kossaibati, M.A. (2014) Is targeted milk sampling an effective means of detecting Johne's disease in dairy herds? Cattle Practice 22(1),26-34
Impact of TB on milk testing
Following the tuberculin test animals may produce antibody that will cross-react in the Johne's antibody test and result in false positives. To avoid this it is recommended that testing is not carried out within 45 days following tuberculin testing. In most cases cross-reactions will disappear within three months and before the next round of Johne's antibody testing. Therefore cows testing false positive as a result of the skin test will eventually return to the low risk category.
Information on the differences between milk and blood testing
Milk and blood ELISA tests have very similar sensitivities. However it is difficult to compare milk and blood results directly as much depends on the timing of the sampling. IgG's are transferred from blood to milk in early lactation meaning that at this stage blood results may be lower than milk results. At peak lactation there may be a dilution effect on the milk ELISA. Overall it is recommended that cows are tested regularly to gain an accurate and up to date profile for each cow. Testing individual cow milk samples taken at routine milk recording visits is a simple and cost effective way of doing this.
Example of pre-purchase questionnaire
It is really important to check the Johne's status of any stock that will be entering the herd. Please follow the link to the Cattle Purchasing Checklist
that will ensure all relevant information is gathered prior to making a purchase decision. Please note the information required to complete this questionnaire can be secured either from the vendor or from the vet responsible for the vendor's herd.