Johne’s disease.

Johne’s Disease is most commonly thought of as a cattle disease; however it can have a significant impact in sheep flocks as well. The main clinical sign is chronic progressive weight loss rather than the pipe-stem diarrhoea seen in cattle.
As many other diseases, such as poor dentition, chronic liver fluke, Jaagsiekte and Maedi are characterised by chronic weight loss, Johne’s cannot be diagnosed on clinical signs alone. A diagnosis of Johne’s is generally only made as the result of investigation into ill-thrift, and, because ill-thrift is not routinely investigated, Johne’s disease is almost certainly under diagnosed in sheep.
Despite this under diagnosis, most National Animal Disease Information Service (NADIS) monthly reports contain a reference to Johne’s in sheep, with most of these reports coming from flocks in the south-east of Scotland. 
In the NADIS database 2.7% of flocks have recorded cases of Johne’s. Taking the under diagnosis into account, this suggests that the level of disease in the UK flock is likely to be as high as, if not higher than, the level of 5% recorded in New Zealand where investigation of ill-thrift is more common.
The NADIS data show a clear difference between lowland and upland flocks in the rate of diagnosis, with none of the lowland flocks in the NADIS database having recorded Johne’s disease, whereas the rate in the upland and hill flocks is 4% of farms. So take care when buying in stock that you don’t introduce it into your flock.