Johne’s could be hampering your flock

Johne’s disease could be going undiagnosed on many UK sheep farms. Gemma Mackenzie finds out more about the problem and what can be done to control it.
Beef and dairy producers are clued up about the threat Johne’s disease poses to their herds, yet many sheep producers are unaware of the fact the disease can affect sheep as well.
In fact, according to independent sheep vet Chris Lewis, Johne’s is a “hidden problem” on UK sheep farms and a disease that is a much bigger issue than previously thought.
However, as sheep farmer Peter Baber, who chairs the English Sheep Health and Welfare Group, points out, it is impossible to know how widespread Johne’s is on British sheep farms because there is no real recording system for the disease in the UK.
He says the failure of many farmers to adopt flock health plans is partly responsible for the spread of this disease and others.
“If proper health planning and quarantine procedures were put in place, we could control a lot of the disease on our farms, including Johne’s.”
Sheep affected with Johne’s show signs of wasting, which is often misdiagnosed as liver fluke or cheek teeth. It generally only affects sheep over a year old. And because many farmers don’t get culled animals post-mortemed, the disease often goes undetected in flocks.
“If you have wasting sheep that are not responding to a flukicide and you check and it’s not cheek teeth, then blood test them for Johne’s. And if you get to the point of culling, I would really recommend a post-mortem,” says Mr Lewis.
This advice is echoed by SAC regional vet manager, George Caldow. “I think anybody who has a thin ewe problem should have a sample of those animals post-mortemed on a regular basis. However, the issue we have is that the level of wastage in ewes will very much depend on the environment they are kept in,” he says.
Transmission
In the same way Johne’s passes between cattle, transmission between sheep is via infected faeces and contaminated waterways – this is particularly relevant during lambing time, when newborn lambs can contract the disease from infected ewes’ faeces.
There is also evidence of a wildlife reservoir of the disease in rabbits. As a result, farmers are advised to cull them hard and continuously if they have a rabbit problem that they think is linked to Johne’s on their unit, says Mr Caldow.
In addition, it is also possible for the disease to be transmitted from cattle to sheep and vice-versa.
Mr Caldow says: “When I speak to cattle producers tackling Johne’s, I tell them not to ignore sheep and to do their best to ensure sheep and cattle are not co-grazing. This helps for control of other diseases, too.”
Treatment
It is not possible to cure sheep of Johne’s, and control measures are limited to removing any animals showing clinical signs of the disease, and looking at flock management to try to control the threat of the disease coming into the flock, says independent sheep vet Paul Roger.
“Usually if you have got Johne’s in the flock, it is a chronic disease. And if you are getting rid of anything from the flock due to wasting, it’s worth getting them post-mortemed to find out what the reasons were for the wasting,” he adds.
A vaccine is available for treatment of the disease – Guidar. It was originally developed for use in sheep in Spain, and there is efficacy data available and reasonably good reports of its usage in sheep.
According to Mr Caldow, the use of this vaccine is more relevant in small pedigree flocks, but in large commercial flocks it may be more worthwhile for producers to vaccinate the ewe lambs they are retaining.
Independent sheep vet Kate Hovers says control of the disease is possible without having to vaccinate the whole flock, if farmers are rigid in their culling regime when Johne’s is discovered in the flock.
“The difficult thing about Johne’s is that the animals are infectious before you know about it. So the sooner you recognise it in your flock and cull out infected animals, the better,” she says.
“I have never used the vaccine, mainly because by using culling I have managed to keep the disease under control.”
Johne’s in sheep: key points
• Johne’s disease causes wasting in sheep
• It is often misdiagnosed as liver fluke or cheek teeth
• Blood testing is not accurate, so post-morteming is essential for diagnosis
• Culling out infected ewes can curb the problem
• Vaccination will prevent wasting but not cure the flock of the disease – consider vaccinating replacement ewe lambs
• The disease can be spread between sheep and cattle
Researcher’s viewpoint
Principal research scientist Karen Robertson, at the Moredun Institute in Edinburgh, has been working on diagnostic tests for Johne’s disease, principally in cattle.
She says farmers contacting her with a problem with Johne’s in sheep are generally those who keep cattle, and graze sheep on their pastures once the cows have gone indoors.
“These farmers often test their cattle but forget about their sheep, and in a lot of instances they can get a breakdown in the herd because they overlook the sheep.”
She says there are two types of the disease in sheep – pauci-vacillary and multi-vacillary. The pauci strain shows up with fewer bacteria, less antibodies and is shed less in the sheep’s faeces, making it harder to detect with diagnostic tests. Meanwhile, the multi strain shows up a huge number of organisms and antibodies and in some cases results in scouring.
“It’s a very difficult disease, because there will never be a single test to detect it, particularly in sheep, where there are two different types of the disease,” adds Dr Robertson.
In addition, she says the previously understood information regarding the strains of the disease – type 1 in sheep and goats, and type 2 in cattle – may be wrong, as evidence in New Zealand uggests the type 1 strain is now affecting deer and cattle.
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