Johne's Disease in Sheep
SRUC Veterinary Services recorded 837 diagnoses of Johne’s disease in sheep between 2005 and 2019, with wasting being the most common symptom. The condition was confirmed in 37 different breeds, as well as 8 cross breeds.
The number of diagnoses fluctuate throughout the year, with few in the summer months. Peaks in February and September are associated with the investigation of thin ewes that are barren at scanning, and thin ewes that fail to gain condition after weaning. Ewes entering the later stages of pregnancy, as well as seasonal feed shortages, may contribute to the higher number of diagnoses in late winter. The graphs below summarise Johne’s disease diagnoses by age and sex for hill and lowland breeds; illustrating that it should be considered as a cause of ill-thrift in all ages of ewes and tups.
50.5 percent of diagnoses were based on blood testing, 34 percent on examination of carcases, and 14.4 percent following examination of faecal samples. Cases of Johne’s disease can be classified as multi-bacillary or pauci-bacillary based on the number of Johne’s disease bacteria within the intestinal wall.
Multi-bacillary cases are associated with large numbers of bacteria and are more likely to test positive on both faecal examination and blood tests than pauci-bacillary cases. They may also cause yellow/orange pigmentation of the intestines which is visible on post-mortem examination.
Pigmented Johne’s disease
The detection of pigmented strains (multi-bacillary) varies by region, and knowledge of the most common strain type occurring on a farm, or within a local area, can help guide the selection of diagnostic tests. Pigmented strains of Johne’s disease are considered to be sheep-associated, with a lower likelihood of infecting cattle. They are therefore of less risk to the health status of cattle utilising the same grazing.
Heather Stevenson (SRUC Veterinary Investigation Officer, Dumfries Surveillance Centre)
Posted by SRUC Veterinary Services on 01/07/2020