Paying attention to manure exposure is a crucial component in controlling Johne's Disease in cow-calf herds, explained Russ Daly, Professor, SDSU Extension Veterinarian, State Public Health Veterinarian.
"It's the manure that serves as the source of bacteria for uninfected cattle," Daly said. "Since Johne's Disease primarily affects the intestine, an infected animal sheds the bacteria (Mycobacterium avium subsp. paratuberculosis) through their manure.
While often considered a condition of dairy cows, Johne's Disease has increasingly been identified as a concern for beef producers, Daly explained.
Animals affected by this disease show signs of diarrhea and progressive weight loss, often in the midst of a normal appetite. "These animals are culled from the herd before they become debilitated, but worse yet, they serve as the source of disease to others within the herd," Daly said.
He explained that typically, it's a young calf that is the most likely to become infected with the bacteria. "However, Johne's Disease is such a slowly progressing condition that signs don't show up until the animal is much older: often 3-4 years of age or more," he said.
Knowing this, Daly said the key to decreasing Johne's Disease transmission comes down to preventing young stock from coming in contact with manure from potentially infected animals. "Preventing young stock from having excessive contact with manure from the cow herd can seem to be a daunting task, but a critical one if Johne's Disease is to be controlled within a herd," Daly said.
Keep Calving Areas Clean
While preventing all contact with manure is not feasible in a cow-calf operation, there are some actions that producers can take to reduce this contact.
"Infectious disease transmission often comes down to a numbers game: the fewer bacteria in a calf's environment, the lower the likelihood of disease," Daly said. "Anything we can do to reduce these numbers stacks the deck in favor of health over disease."
The calving area is especially important when it comes to transmission of Johne's Disease.
"Newborn calves are particularly vulnerable to the bacteria entering their bodies, where they begin the slow steady progression to clinical disease that may appear years later," Daly said.
Risky conditions for calving areas include: use by multiple cows at the same time (rather than individual pens); manure buildup; dirty conditions that contribute to soiled udders; and cows with clinical Johne's Disease or other illnesses nearby or in the calving area.
As young calves are paired up with their mothers and leave the calving area, exposure to manure remains a threat for the transmission of Johne's Disease.
Conditions for nursing beef calves that contribute to Johne's Disease exposure include: cows with clinical Johne's Disease running with cow-calf pairs on pasture; manure buildup; conditions that contribute to manure contamination of water sources (stock dams and creeks rather than water tanks); conditions that contribute to manure contamination of feed (feeding on ground rather than in bunks or feeders); cows sick from other illnesses running with cow-calf pairs on pasture; and use of equipment (skid steers, loaders, etc.) contaminated with manure from the cow herd.
As cattle get older, Daly explained that their resistance to new infection with Johne's Disease bacteria increases. "However, even weaned calves can become infected, particularly if exposure levels are high," he said.
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