One of the biggest problems surrounding Johne’s disease control is the difficulty of detecting infected animals that may not be showing any signs of illness.
Sheep farmer Andrew Hodgson runs 1,500 predominantly Masham ewes and 300 Texel cross Mule ewes on downland on the Isle of Wight.
He buys in all replacements and finishes lambs throughout the year at Cheverton Farm, Shorwell.
He is very aware of the effect of hidden diseases, having inadvertently bought in maedi visna-infected stock, a move that cost the farm around £75,000.
The disease was identified through blood testing after several years of poor lambing percentage and higher-than-desirable levels of thin ewes.
Since then, regular screening of thin ewes at scanning has been carried out to identify and monitor MV, with poorer ewes culled. All bought-in animals are also screened.
Johne’s infection had been identified on occasion, but it was only in the autumn last year when the disease was flagged up in a group of 350 ewes.
His vet, Hannah Kenway suggested screening the ewes for Johne’s, worms and energy deficiency after they struggled to hold condition after weaning.
On this occasion, low-quality grass was a factor, but the test also picked up two Johne’s-positive animals.
As a result, Mr Hodgson tested a sample of poor-condition, bought-in replacment ewes and identified Johne’s-positive animals from two sources.
Challenges of sourcing stock
The challenges of sourcing Johne’s-tested stock has since been part of the reason he has chosen to start using Cheviot Mule ewes, instead of Mashams.
He adds: “As a commercial sheep farmer, it would be worth a modest premium to know animals are clean of Johne’s and maedi. I’m not looking at full certification, but a conversation with the breeder that they blood test and look for it and do something to keep an eye on it in the flock. That would give me peace of mind.”
Putting in place a control strategy
- Dag ewes at lambing
- Keep pens clean at lambing and adopt low stocking rates
- Test bought-in animals
- Be aware of disease risk when co-grazing – don’t graze young lambs on cattle grazing
- All bought-in stock should be quarantined for general disease control, but this does not help with Johne’s, as it’s not spread between adult sheep
Having faced the fear that Johne’s would have a similar financial effect on his flock as MV, Mr Hodgson is currently in the process of designing an appropriate control strategy with Mrs Kenway.
As well as MV, bought-in stock are now routinely screened for Johne’s. It is also included as part of the annual screen of 10-20 poor-condition ewes at scanning.
Any ewes that are unexpectedly thin, despite being wormed and provided with good nutrition, will also be culled as a precaution.
He is also considering vaccinating incoming young sheep against the disease.
Mr Hodgson believes other sheep farmers should take the same approach.
“I think everybody who doesn’t have a closed flock should blood test a sample number of sheep every year for maedi visna and Johne’s.
If you have it in your flock and it gets to a high percentage level, you have a flock you are losing money on, with lower lambing percentages, higher mortality, lower cull sales – you’re losing money on every facet.”
What is it?
Johne’s is caused by the bacteria Mycobacterium avium paratuberculosis (MAP).
How is it spread?
MAP usually infects animals around birth. The most common route is by mouth, such as lambs eating faeces or drinking infected colostrum.
Dirty udders, bedding and infected water pose a risk. It may be spread in utero and can be spread between sheep and cattle and vice versa.
Clinical signs of the disease usually show as thin ewes that struggle to put on condition.
When clinical signs are seen, there is likely to be higher levels of subclinical disease.
Subclinical disease limits production through reduced growth. Immune suppression may also lead to higher levels of diseases, such as mastitis.
Bacteria can lie dormant, so an infected animal can look healthy and test negative.
They then might start shedding bacteria when they are two to three years old, while still looking normal. By the time they are clinical, they may have been spreading the disease for some time.
You can test for Johne’s using blood or faeces. SRUC offers a 12-ewe blood screen for MV for commercial farmers, costing £37. Johne’s can be added for £3.50 a ewe.
A pooled 10-ewe faeces sample costs £73. Faeces or blood testing sensitivities can vary farm by farm. Speak to your vet about appropriate testing strategies.
When to test
Routine screening of 10 thin, poor-looking cull ewes should be carried out at weaning.
The disease is hard to eliminate unless doing a whole-flock cull, which is rarely financially viable. Instead it’s about damage limitation.
This may involve targeted culling of thin ewes and ongoing monitoring. Vaccination can protect sheep and reduce the shedding of MAP and could be used on four- to six-month old sheep when flock disease incidence is more than 5%.