Voluntary Johne’s control coming to Canada

(Adapted from Ontario Dairy Farmer)

A voluntary, nation-wide program to identify and control Johne’s in dairy and beef cattle could be in place as early as January 2003. The Canadian Animal Health Coalition’s working committee for Johnes Disease recently approved final details of the control program in Winnipeg and will present it to the coalition in December. However, they also agreed there should be another national forum before the program is introduced, so it won’t likely be launched until mid-2003.
The program will be national because the country’s Johne’s status affects livestock exports, and because of the ease of administration. It will be very similar to the volunteer program initiated a year ago in Alberta.
The Canadian proposal has three components: promoting producer awareness of best management practices, herd testing for Johne’s, and disease control and reduction. The provincial veterinary services are committed to testing.

Control requires testing

The American program recommends testing all cows at the end of lactation, but the committee is recommending that a random sample of animals three years old and beyond will be sufficient. As the animals get older, the tests become more reliable.
There will probably be a combination of tests being used. At this point in time, either blood or fecal samples are approved. Testing 30 cows in herds of less than 100 animals, 40 cows in herd of 100 to 200, and 50 cows in the herds of more than 200 will give a representative sample. It may be possible to pool five blood samples in one culture and pool manure samples from five to 10 cows to reduce costs without compromising results. Producers’ costs will likely range from $210 to $350 for testing 30 to 50 animals.
Tested herds will be classified as low, medium and high prevalence herds and herds will be able to move from level one through four as they test negative for Johnes over time. It’s not clear how prevalent Johne’s is in Ontario. A sample drawn from the Sentinel herds, which is not random, suggests that 2.2 per cent of cows and 37 per cent of the herds in the province will have Johne’s. Probably 49 per cent of herds in Canada have at least one Johne’s positive cow.
The prevalence in the U.S. was initially estimated at 22 per cent herds, then increased to 40 per cent as testing results came in.

Bacterium persistent

The disease is spreading because of the way herds are managed, and the way cattle are moved between farms, and between countries. Managing cattle in large groups, increases the incidence of infections and the practice of feeding surplus milk to calves enables one cow to infect many others.
Johne’s disease, or paratuberculosis is a very persistent mycobacterium that can exist in dairy herds for years without any animals developing a clinical case. When the bacterium becomes active, the animal suffers diarrhea and weight loss. The organism can be transmitted in utero, in colostrum, in milk and in feces. It also travels in feed and water.

Hygiene is critical

Risk to humans

The consequences of human exposure are still unclear. The link to human health is through Crohns’ disease (which impairs the intestine’s ability to absorb food), but there’s as many reports that say there’s no link as say there is. There have been studies suggesting that Crohns and Johnes were linked until recently, when a researcher from the United Kingdom presented contrary evidence at seminars in Ottawa and Guelph.

Posted Jan 9th

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