Science Report
Agricultural and Consumer Press Service
440 Henry Mall
Madison WI 53706
(608) 262-1461
College of Agricultural and Life Sciences
Research Division
University of Wisconsin-Madison
For Immediate Release
For More Information:
George Shook (888) 400-8050 [Toll Free]
shook@calshp.cals.wisc.edu
Nationwide Johne's Disease Survey
Hits Halfway Point
Researchers at the University of Wisconsin-Madison are approaching
the halfway mark in a nationwide survey of dairy producers that's
part of an effort to prevent Johne's disease. Cooperating dairy
producers will get free confidential testing of their cows, and
they'll be helping to reduce the impact of a disease that costs
the U.S. dairy industry hundreds of millions of dollars every year.
"Johne's is a good candidate for prevention by genetic resistance
because vaccines for the disease are only partly effective, and once
cattle get the disease there is no cure. The only way to control
this disease is to prevent it," explains dairy cattle geneticist
George Shook, who leads the team of UW-Madison researchers. They
hope to identify three to five genes that are involved in the resistance
and susceptibility to Johne's disease. Applying this knowledge would
allow producers to select AI sires whose daughters are resistant to
the disease.
Using tools of molecular genetics, the researchers are genotyping the
daughters of 12 prominent Holstein bulls, located in herds throughout
the country. The bulls were selected because they have large numbers
of daughters -- up to 50,000 -- in production in herds on the Dairy
Herd Improvement program. The bulls themselves are not diseased.
Johne's Survey
The researchers are contacting herds that have five or more daughters
of the 12 bulls (about 10 to 15 percent of DHI herds). "So far we've
tested close to 4,000 cows. We want to test 6,000 more to reach a
total of 10,000. We have a long way to go, but continued good cooperation
from producers will help us get there. The more cows we test, the more
genes we'll be able to discover," Shook says. "We have identified more
than 220 disease-positive cows; most of these were not previously known
by the producer to be infected. The information allowed producers to
take action appropriate to their situation to prevent the spread of
disease to uninfected animals.
"We're making our final contacts with producers now and will complete
those contacts by March 2003. When people get our letter and information
about the project, we hope that they will reply positively and be willing
to sign on to the project," Shook says.
The research project will pay for the disease testing -- a $25 benefit
for each cow tested. In addition, for every project cow tested, producers
can select another non-project cow for a free test. Test results are returned
to producers for use in controlling the disease in their own herds. Shook
adds that the results are confidential, and won't be shared with anyone
but the cooperator.
"Herds that know they have animals with Johne's disease are especially
valuable to us and we know that these herds can benefit from the testing
that we do," he says. "We would also like to work with herds that have
recently tested in other Johne's disease programs. In these cases we would
need only a blood sample for DNA analysis and the test results for project
daughters.
"Herds that don't know their disease status should participate too. Many
of these herds have the disease, but don't know it. We want to test them,
too, for the benefit of our project and to help these herds begin to get a
handle on controlling Johne's disease. Every day that passes, some of the
daughters we want to test are being removed from herds, so it's important
that we move ahead as quickly as we can to be able to test as many daughters
as possible."
The project hasn't gathered enough samples yet to be conclusive, but Shook
has already noticed one intriguing result: Prevalence of the disease among
bulls' daughters ranges from a low of less than 2 percent to a high of nearly
12 percent. "If these differences stand up through additional testing, we'll
have some interesting and valuable comparisons to explain," he says.
The data collected during this study will be useful in other areas of dairy
health as well. "We're beginning to understand that the DNA samples we're
collecting will be useful for many more studies beyond genetic resistance
to Johne's disease," Shook says. "For example, we'll use these genotypes
to search for genes associated with mastitis resistance as measured by
somatic cell count and for genes associated with reproductive performance
as measured by calving interval or days open. The serum samples we use for
disease testing could be used to assay for antibodies to another
infectious disease."
The researchers plan to contact herds in the Eastern states and Wisconsin
during November and December, Central states in January 2003, and Western
states in February 2003.
The USDA Initiative for Future Agriculture and Food Systems is providing
most of the support for this study. The researchers also have received
support from National Association of Animal Breeders and a Hatch grant
from the UW-Madison College of Agricultural and Life Sciences.
JOHNE'S DISEASE—A Stealthy Profit-Killer
Johne's is a slowly developing, incurable disease caused by a chronic
intestinal infection. The infection interferes with an animal's ability
to absorb nutrients from food. The disease is also called paratuberculosis
(after Mycobacterium paratuberculosis, the bacterium that causes the infection).
Animals become infected as calves from contact with adult cows that have
Johne's disease. The disease develops gradually over a period of two to
five years, and the signs can be subtle. Cows have diarrhea and lose weight,
and milk production falls. These signs don't become obvious until the disease
reaches advanced stages. Often animals are culled because of low production,
but sometimes the cause of that low production is Johne's disease. Meanwhile,
calves on the farm continue to become infected.
The Wisconsin ag department estimates that state dairy farmers lose $54
million annually in lost milk production and reduced slaughter weight;
nationally, the toll exceeds $200 million. Many states are increasing their
efforts to help producers identify the disease in their herd and to begin
strategies to bring the disease under control.
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