Ovine Johne’s disease (OJD) is one of the UK’s biggest but least known threats to flock health.
It is thought that some 70 percent of UK flocks harbour the disease; a study in the UK in 2019 showed that 64 percent of sheep flocks tested, were positive for Johne’s.
To explore the implications of this “iceberg disease” in sheep, Virbac recently partnered with Farmers Guardian to assemble leading authorities and independent sheep farmers for an in depth round table discussion on the negative and costly effects of Johne’s disease.
The panel:
- Bizza Walters, mixed family farm in Warwickshire, lambing 600 North Country Mules to Suffolk tups
- Ioan Humphreys, sheep, beef and poultry farmer in Powys, lambing 850 ewes
- Fiona Lovatt, specialist independent vet in sheep health and production and a clinical associate professor at the University of Nottingham
- Ben Briggs, session chair, Agriconnect group publisher
- Dr Peers Davies, vet and researcher at the University of Liverpool, specialist in Johne’s disease
- Maddy Lewis, sheep farmer near Aberystwyth, lambing 300 ewes and selling rams through Innovis
- Ben Strugnell, independent vet running carcass-based diagnostic service Farm Post Mortems
The round table identified a worrying lack of awareness of Johne’s disease in sheep, with flockmasters shocked to discover its existence and the extent of the problem, a situation that highlighted the need for vets and farmers to collaborate to tackle this common chronic wasting disease caused by the bacterium Mycobacterium avium subspecies paratuberculosis (MAP), which causes inflammation of the gut so animals are unable to absorb nutrients.
Peers explained some of the ramifications of Johnes disease if left undetected: “Ewes will be metabolically inefficient, and this makes them less likely to get in-lamb,” he said. “They will probably be culled as barreners before they have lost enough weight to become an obvious case. People will not realise why ewes are not getting in-lamb; they will attribute it to worms or fluke”.
Bizza agreed, saying that a thin ewe would most likely be attributed to worms rather than ovine Johne’s disease being considered, and that her flock has never been tested.
“If thinness is a major reason for culling in your flock, it is a sign ovine Johne’s disease should be investigated”, said post-mortem specialist Ben Strugnell.
For every animal showing clinical symptoms of ovine Johne’s disease, a further 10 to 15 will be shedding the bacterium but not showing any visible symptoms. Within a flock, infection rates can range from two or three percent of animals affected, up to 75 percent. An infected flock will typically have a replacement rate of about 30 percent, compared with 22 to 24 percent for an uninfected unit. “
That is a huge additional cost, so understanding the economic importance of ovine Johne’s disease in a flock is essential, and something vets could be helping clients with”, said Peers.
Powys sheep, beef and poultry producer, Ioan Humphreys, said: “I knew about Johne’s in cattle, but had no idea about sheep and, looking back, I had a ewe a couple of months ago which had classic signs of it.
“We have a closed flock, health plans and regular meetings with our vet, but this has never been mentioned.”
Maddy added: “If we have ewes with ovine Johne’s disease who are piling out worm eggs all year round because their immunity is compromised, it is another reason to vaccinate”.
Sheep vet Fiona Lovatt asserted that testing was key: “If you do not look, you will not find it, and people often just get rid of thin ewes.
“While vets might offer the cheaper option of blood testing, by far the most reliable result would be from sending in some pooled faecal samples from ewes suspected of having might have ovine Johne’s disease and to perform a pooled PCR test.”
Once a flock is infected with Johne’s eradication is almost impossible, so the aim is to control the disease by reducing the build-up of bacteria on the pasture therefore transmission.
Although there is no licensed vaccine for Johne’s in cattle, there is a licensed vaccine for Johne’s in sheep.
Gudair is a one-shot lifetime vaccine and whilst vaccination won’t eliminate the bacteria nor remove all an infected flock’s problems overnight, it has been shown to be a very effective way of controlling Johne’s and significantly reducing the impact of the disease in infected flocks.
“The round table demonstrated the need for vets to consider Johne’s in any unthrifty stock and include this in discussions when working with farmers to protect flock health, this is now of increased importance as the AHWP has set the control of iceberg diseases in sheep as a priority,”” said Sabrina Jordan, farm product manager, Virbac UK. “Ultimately, controlling ovine Johne’s disease in a flock will increase productivity in the long term.”
“The benefits being; potentially fewer barreners; increasing productive life of the ewe for an additional one to two years and increased bodyweight at slaughter.
“In addition to this, there can be cross-over of Johne’s from sheep to cattle, so by controlling OJD in flocks, potentially you can help protect herds on mixed farms.”
For Ben Strugnell, the disease is the number one he believes sheep producers should be tackling. He said: “For me, it is ovine Johne’s disease first and all the others second, for two reasons. One, it is highly prevalent, and two, you can actually do something about it.”
For more information about Johne’s disease in sheep, head over to NADIS or find out more from experts and sheep farmers’ experience of ovine Johne’s disease at Farmers Guardian.
