Johne’s disease is a long-standing disease which causes gradual wasting and production loss in cows as they get older.
Given its prevalence, most farmers will have Johne’s disease in their herd at some stage. The first sign of a problem is often watery, green diarrhoea that bubbles after it touches the ground or chronic wasting seen in older cows.
If you discover a Johne’s problem in your replacement heifers, it’s likely that your farm has a high burden of the disease bacteria. The more heavily infected cows you have, the more they will continue to shed the bacteria and infect your younger stock.
Although it is caused by bacteria (a particular strain of Mycobacteria), Johne’s cannot be cured with antibiotics. These bacteria can survive in moist, shady conditions for up to 12 months and can be transmitted by other wildlife, including rabbits, hedgehogs and possums.
How do you know if a Johne’s problem exists on your farm?
If you’re culling at least 1% of your older animals for chronic wasting, it’s likely a Johne’s problem exists amongst your herd. A blood test is an easy way to check if a wasting cow is carrying Johne’s disease.
If you’ve had several cows confirmed to have Johne’s disease in one season, testing your herd test milk samples is a great way to assess the overall status of your animals.
If you have a Johne’s problem, how do you control it?
Johne’s disease can be managed through effective strategies and, with persistence, it can eventually be eliminated from a farm.
Here are some management plan tips for your herd and calves:
Management plan for herd
Get milk samples tested and depending on results...
Cull highly positive cows immediately. These cows are likely to become clinically sick in the near future and will be shedding large numbers of bacteria. These bacteria can survive on pasture for a long time, creating a lag effect on disease incidence in the herd and infecting replacement calves. It’s very important that a paddock, where sick Johne’s cows are held while awaiting disease confirmation is not used by calves in the future.
Confirm positive cows with a blood test, before deciding to cull. If there are too many cows to cull all at once, a decision may be to maintain them for now, but keep them separate from the herd. Colostrum and milk from these cows should not be fed to replacement calves or any other calves being kept.
Re-test cows with suspect results to confirm the presence of Johne’s disease and ensure accurate diagnosis before making a decision about them.
Management plan for calves
Calves under 12 months old have the highest risk of Johne’s disease infection due to low immunity. Between 10-40% of calves born to clinically infected cows may already be infected at birth.
Calves can contract the disease through exposure to infected faeces or by consuming infected colostrum. Regularly rotating the herd onto clean paddocks during calving can help minimise calves’ exposure to infected faeces. Once they’re brought to the calf shed, it’s critical that calves are only fed colostrum from Johne’s-negative cows.
When putting your replacement heifers out on pasture, it’s vitally important they aren’t exposed to adult cattle faeces, as this is the main cause of infection in post-weaning calves. Although Johne’s bacteria can survive in soil for up to 12 months, this risk does decrease significantly after three months as calves grow stronger immunity.
So, to minimise infection, youngstock should only graze paddocks that haven’t been used by adult cattle in the past three months. When sending young cattle to graziers, they should be kept separate from carry-over cattle. It’s also important to keep calves away from paddocks that have had effluent spread on them.
As well as through paddocks and milk, Johne’s disease can spread through water too. Only clean, fresh water should be supplied to youngstock, and access to open water sources, such as rivers and dams, should be prevented by fencing. Even if there are no adult cattle grazing upstream, Johne’s disease can be spread by wildlife, who can contaminate the water source.
Johne’s disease causes major losses in badly affected herds. By testing and managing this disease now, we can reduce future losses from this untreatable disease.
