Veterinarians say it is particularly important for producers to protect the health of their female replacement animals
When people find that they have Johne’s in their herd, they need to figure out how to deal with it.
Dr. Karin Orsel, a veterinarian at the University of Calgary, says producers can test their entire herd but they won’t find every infected animal.
“So your strategy would be to determine which animals are most likely clean and not yet infected.
“Your first and second calvers will probably not be shedding yet. The ones that you don’t want infected are your female replacement animals.
“In a commercial herd, the male calves are leaving — going to a feedlot — so we don’t need to worry about them. The cows with steer calves at foot can graze anywhere. The steers will go to a feedlot and be slaughtered before infection can become established. But the cow with a heifer calf (that might become a replacement female) should graze on the cleanest pastures available,” says Orsel.
If you are calving in May and cows are out in big pastures, there is less fecal contamination of the environment.
“If you calve in February or March, and the animals are confined closer to home, you’ll have more spread of disease within the herd, infecting your replacement heifers, and this disease will stay in your herd,” says Orsel.
“This is especially true in purebred herds because they tend to calve earlier.…
“I sit down with the producer and help make a plan. If a pasture has been mowed for hay and not grazed for a while, it’s probably clean; this might be where you turn out the cows with heifers at foot, or the younger animals you want to keep free of disease. It pays to strategize. If you have a closed herd and don’t bring in other cattle, you won’t get it into your herd. But if you already have it, you can manage it. Management options will depend on herd size, how much pasture you have, etc.”
Producers who keep replacement heifers should think about how to keep them clean and healthy.
“It can be difficult, however, because you don’t want to turn heifers out into the foothills by themselves to calve (even though it may be your cleanest pasture) with risk of losing calves to predation. Young heifers are not always aggressive enough to protect their calves. People often put some older cows with them, to deter predators,” she says.
“You also need to think about how you select replacement heifers. Most people have a plan for weaning and selecting heifers, and don’t just select on size and weight.
“There may be certain genetics, certain cows they like, and pick heifers from those. Think about dealing with that group a bit different; bring them to pastures that are clean. If there is a suspicious cow, keep her out of that pasture. If you spend money on testing, make sure you keep the test-negative animals together, and try not to have a chance for a positive animal to be in that group.”
Orsel says if a cow tests positive, producers should cull it and also its female offspring because it exposed them while they were calves. Its daughters, whether weaned heifers or young cows, may not test positive yet, but likely are incubating the disease and will spread it to other herd members.
There are tactics that can slow down this disease.
“It just takes a lot of thinking, and sorting,” Orsel says.
This can minimize risk for replacement heifers, which would be the ones that would later spread the disease if they happened to be infected as young animals.
Dr. Steve Hendrick of the Coaldale Veterinary Clinic in Coaldale, Alta., did a study with monensin a few years ago. This ionophore, a type of antibiotic that hinders the function of bacteria and their ability to reproduce, is often used as a feed additive to help prevent bloat and coccidiosis and improve rumen function.
“This product tends to hinder the bacteria that cause Johne’s so if people are using it for coccidiosis control in adult cows, it may also reduce the shedding of Johne’s. It is not a cure, but may help minimize contamination, affecting the number of live bacteria that are shed.”