Losses of adult sheep due to ovine Johne's disease in 12 infected flocks over a 3-year period.
OBJECTIVE
To measure the biological and financial impact of ovine Johne's disease (OJD) mortalities on 12 infected flocks within the endemic area of southern New South Wales over a 3-year period.


METHODS
An observational study was conducted over a 3-year period from 2002 to 2004 on sheep from 12 OJD-infected flocks from southern NSW. Flocks ranged from between 3,500 and 20,000 sheep. At the start of the study owner estimates of OJD mortality were 5% or greater.


METHODS
Annual mortality rates were estimated from farm records provided by owners. The proportion of OJD mortalities was assessed after histological examination of tissues collected from dead and moribund sheep during 5-day necropsy inspections conducted in autumn, winter, spring and summer in 2002. The financial impact was estimated using a gross margin analysis for each of the three study years and by placing a financial value on the necropsied sheep.


RESULTS
On the 12 farms, the average OJD mortality rate was 6.2% (range 2.1% to 17.5%) in 2002, 7.8% (range 1.8% to 14.6%) in 2003 and 6.4% (range 2% to 11.9%) in 2004. The average decrease in gross margin due to OJD infection on a farm in 2002 was 6.4% (range 2.2% to 15.4%), 8.5% (range 3.1% to 15.8%) in 2003 and 7.4% (range 1.5% to 15.4%) in 2004. This equates to an average reduction in annual income of $13,715 per farm per year. OJD losses accounted on average for two thirds of the total estimated financial loss associated with sheep deaths.


CONCLUSIONS
This study demonstrates the significant biological and financial impact of OJD on sheep flocks. These findings are of relevance to all Australian sheep flocks infected or at risk of OJD infection.
Bush
R D
RD
Farm Animal Health Group, Faculty of Veterinary Science, University of Sydney, PMB 3, Camden, New South Wales 2570.
Windsor
P A
PA
Toribio
J-A L M L
JA
D017677:Age Distribution; D000818:Animals; D001344:Autopsy / Q000662:veterinary; D002423:Cause of Death; D005260:Female; D008297:Male; D009517:New South Wales / Q000453:epidemiology; D010283:Paratuberculosis / Q000191:economics / Q000401:mortality* / Q000473:pathology; D011159:Population Surveillance; D012621:Seasons; D017678:Sex Distribution; D012756:Sheep; D012757:Sheep Diseases / Q000191:economics / Q000382:microbiology / Q000401:mortality* / Q000473:pathology