Keeping Ovine Johnes Disease out of a Flock Note Number: AG0965 Published: September 2006 Updated: January 2011 A few simple precautions will significantly reduce the risk of ovine Johnes disease (OJD) entering a flock. Avoid purchasing infected sheep The greatest risk of introducing OJD into a flock comes from the introduction of infected sheep. Introduced sheep may initially show no obvious signs of OJD but may be shedding the bacteria in their manure and contaminating pasture. The best way to minimise the risk of introducing OJD is to maintain a closed flock. However, if purchasing sheep, the risk can be minimised by purchasing from low-risk flocks. The ABC Score Under the Assurance Based Credits (ABC) Scheme, every mob of sheep in Australia has an ABC score. This score indicates the risk that sheep may have OJD. The higher the ABC score, the lower the risk that the mob has OJD. Purchasing sheep from flocks with a high ABC score means the risk of introducing infected sheep is minimised.  (Refer Agriculture Note: AG1156 Assurance Based Credits (ABC) Scheme and the Sheep Health Statement). Victoria is divided into two Prevalence Areas. Medium Prevalence Area. The following shires are situated in Victoria's Medium Prevalence Area: Swan Hill, Mildura, West Wimmera, Glenelg, Yarriambiack, Horsham, Gannawarra, Buloke and Hindmarsh. Owners of flocks in these shires can claim 2 credit points in Category A of the ABC score (unless the flock is infected or suspected of being infected). High Prevalence Area. The remainder of Victoria is