Control Options for OJD Infected Flocks

Note Number: AG1082
Published: February 2005
Updated: June 2013 

There are a range of management options available to assist control ovine Johnes disease (OJD) in infected flocks.

Managing OJD

In the first few years after OJD enters a flock, it may cause very few deaths. Losses usually become more significant with time. When OJD has established in a flock, death rates due to OJD alone are commonly around 2-3% a year. Some flocks, however, have experienced much higher losses. These flocks tend to have had OJD for many years.
Producers should consider all options carefully, particularly in terms of the long-term effect on the farm business.  Factors that should be taken into account include current and expected stock losses, and trading implications for the farm business.

Management options

A Property Disease Management Plan (PDMP) should be carefully designed for each individual property. The main principle is to reduce the exposure of sheep (including neighboring flocks) to the OJD-causing bacteria, Mycobacteruim paratuberculosis. This applies to all sheep, but especially younger animals. Methods to control OJD include:

• removing sheep showing obvious signs of OJD as soon as possible, to reduce contamination of pastures.
• keeping animals in good health by controlling internal parasites, ensuring adequate nutrition and avoiding other forms of stress.
• considering culling high-risk mobs that are more likely to contaminate pastures.
• vaccinating against OJD. Vaccination against OJD significantly reduces death rates and the numbers of bacteria shed by infected sheep.
• conducting an Infected Flock Profile test will assist in identifying high-risk and low-risk groups within the infected flock. Low-risk sheep can be used as a breeding nucleus as well as useful buffers between neighboring properties
• grazing management strategies to avoid high stocking rates on very short pastures.
  Cropping or grazing cattle on land contaminated with OJD bacteria, can reduce contamination.
• avoiding lambing on heavily contaminated areas.
• vaccinating replacement sheep and weaning onto lower-risk pastures. These include areas that have not been grazed by high-risk mobs. OJD bacteria survive longer in damp shady areas, such as around dams, springs or swamps.
• avoiding yarding low-risk sheep in heavily contaminated yards. If possible, carry out routine procedures such as marking, drenching and jetting in portable yards. Bring low risk sheep through yards first if portable yards are not available.
• crutching or shearing before lambing to reduce the amount of manure on the udders and legs of infected ewes.
• weaning early to separate lambs from infected ewes.
• avoiding water supplies that are heavily contaminated with manure from high-risk sheep.

Eradication

Careful consideration of all options should occur before destocking an infected property. Destocking is no longer commonly undertaken in Victoria as most producers chose to control OJD in their flocks by vaccinating and introducing other management strategies.
Where destocking is undertaken to remove an Infected status, an approved Property Disease Eradication Program (PDEP) should be completed. The destocked property must remain free of sheep for at least 15 months (including two summers) to allow decontamination of the land.
Alternative enterprises during destocking include cropping and cattle. Short-term grazing of sheep such as store terminal lambs may also be possible.  The use embryo transfer and artificial insemination to preserve the genetics of valuable breeding stock could be an option for some producers considering destocking.

Further information

Further information about OJD can be obtained from the websites www.ojd.com.au OR  http://www.dpi.vic.gov.au/farming/OJD

Acknowledgement

This note was originally developed by Richard Keys and the previous version was published in September 2006.
Reviewed by Dr David Champness, Biosecurity Victoria. January 2010.