Rain Shadow ends - and what is Yonees disease?

I really have been enjoying the Australian Broadcasting Commission's Rain Shadow. Sadly, the last episode is on Sunday.

The story line is simple enough. An enthusiastic young city vet Jill Blake (Victoria Thaine) arrives in the small drought stricken South Australian town of Paringa to work with notoriously "difficult" Kate McDonald (Rachel Ward).

Set to work, Jill immediately encounters many of the problems of dry-land farming in stark relief: a farmer who can cope with neither the drought nor his mounting debts; another forced off his land by the bank; and a third confronting the vexed issues of succession and future planning. Then there's the spectre of a notifiable sheep disease, the mere mention of which turns Kate's prickly attitude to open hostility.

While initially criticised by some critics as too slow moving, the program has evolved into a gripping six part mini-series that has become compulsive watching for my wife and I. However, one thing puzzled me. What was this mysterious "yonees disease"?

Now I grew up in a fine wool merino region and I had never heard of it. Finally, I got so annoyed that I went searching. As best I can work out, it is in fact Ovine Johne’s disease (OJD), a chronic wasting disease of sheep caused by the sheep strain of the bacterium, Mycobacterium paratuberculosis, which grows mainly in the small intestine.

The intestine wall slowly thickens and the animal has increasing trouble absorbing nutrition from its food. A sheep with clinical OJD usually continues to eat and remains bright, but slowly loses condition. There is no cure - the animal usually dies within 3 to 6 months. According to the NSW Department of Primary Production:

Since it was first found in Australia in 1980, Ovine Johne’s Disease (OJD) has proven to be a costly disease in Australia. It spreads slowly, is difficult to detect early on, causes lower weight gain and wool production and can kill about 10% of adult sheep each year if left unmanaged. Recent NZ research has been reported as showing losses of 17% of weaner weight and 10% of wool cut in sub-clinical cases in crossbreds. Once it gets into an area all flocks are at risk. The earlier you act, the less the impact of OJD on your business. Assuring sheep buyers about the OJD status of your sheep is becoming the norm.

Now I feel a little better about not recognising it since it did not exist in Australia when I was growing up.