Reed canarygrass: environmental foe, cattle food?

Cattle graze on reed canarygrass, an aggressive pest plant in Nebraska’s Rainwater Basin. Grazing could keep the invasive species in check and provide economic return to cattle farmers. 

USDA Agricultural Research Service (ARS) scientists may have identified a solution to protect cattle from Johne’s disease (paratuberculosis).

Researchers have developed an experimental vaccine to combat the chronic intestinal disorder that causes diarrhea, weight loss, poor health and even death in ruminants. Johne’s disease most prevalently affects dairy herds, costing the industry more than $220 million annually, but also impacts other cattle, sheep, goats and deer.MAP

ARS microbiologists Judy Stabel and John Bannantine began studying four proteins in the bacterium that leads to Johne’s disease, Mycobacterium avium subspecies paratuberculosis (MAP), rather than using cells of live, but weakened, or dead MAP.

In early trials, vaccinating mice with the proteins reduced bacterial colonization of their intestinal walls and bacterial shedding in feces. Shedding is a major way for other animals to become infected. Cattle grazing pasture with MAP-contaminated manure can become infected, as well as calves drinking colostrum from an infected dam.

After encouraging results from the mice study, researchers scaled up their experiment by producing the four proteins and combining them into a single recombinant vaccine “cocktail” that could be given to calves at doses of 200 or 400 micrograms. Trials with dairy calves produced positive results.

Researchers were careful to avoid mistakes that were made with past vaccines, including a tendency to trigger blemishes at the injection site. Another concern was interference with the accuracy of serological tests that detect both MAP and the bacterium that cause bovine tuberculosis.

The vaccine not only made the calves immune to the disease over a year of monitoring, but the cocktail showed little to no cross-reactivity with serological tests for Johne’s disease and bovine tuberculosis. The cocktail also did not cause any blemishes at the site of the injection, a benefit for animals raised for meat and hide production.

Additional efficacy trials will take place, and researchers are looking toward collaboration with an industry partner to explore potential commercial use of the vaccine. More information on the dairy calves trial can be found in volume 39, issue 23 of the Vaccine scientific journal. — Anna Miller, WLJ managing editor

 

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