There’s been good progress made when it comes to Johne’s control, but there’s still more to do. We spoke to two vets to find out more about the latest tools to help tackle this insidious disease.
TEXT KAREN WRIGHT
Many dairy herds have implemented good Johne’s disease control measures, and seen significant progress in reducing infection rates as well as better herd health. Others still have some way to go and now, backed by retailer pressure, it’s time to step up a gear, according to two Johne’s specialist vets. Latest analyses of Johne’s test results and milk-recording data have been instrumental in the recent progress seen in many herds. PAN Livestock Services has used InterHerd+ to identify ‘relationships’ in this data and the key Johne’s-related parameters that characterise the disease in herds.
This valuable information has been benchmarked across many dairy herds to understand the variation, and has been used by the Johne's Action group to develop a progress tracker for on-farm use. This monitoring tool was incorporated into the main Johne’s-disease UK screening services in July 2021.
“The Johne’s Progress Tracker has been quite a breakthrough in identifying how well a herd is faring in the main areas compared to an industry average,” says vet Peter Orpin, who is also chairman of the Johne’s Action technical group. “It’s lifted the lid on control measures, and highlights where there’s scope for improvement.
“Interestingly, the tracker shows that control in many herds has stagnated. Johne’s is something retailers are concerned about, and the stalling of progress highlights that we need to nudge vets and producers to move to the next stage of controls to make further improvements,” he says.
“The best way to approach Johne’s control is to start by establishing the herd’s disease prevalence and where the key risks of infection lie, and then manage the most important risks. Typically, these are to avoid introducing infected animals into the herd, keeping infected cows separate during the dry period and at calving, removing calves from cows quickly after birth, and avoiding the use of colostrum from infected cows.” Moving on from these first key control strategies is vital to ‘kick start’ further progress.
“This is particularly relevant for herds that have been controlling the disease for some years and are now finding that progress has slowed down,” says Mr Orpin.
“We often find that the main infection risks in these herds are from an infected dam to her own calf, and this can account for up to 60% of new infections. This can be reduced by only breeding replacements from ‘test negative’ cows with no history of Johne’s. These are the lowest risk cows in the herd.”
Mr Orpin reinforces the need to be meticulous about tagging any ‘test positive’ cows and calves because these are the highest-risk animals, and must be separated from low-risk cows and calves.
“Ensure the standard risks are managed first and then tighten the screw on the weak links in the control chain,” he says.
“Calf-to-calf spread of Johne’s is possible, and herds wanting to go that extra mile are now tagging calves from ‘test positive’ cows and keeping them separate from ‘green’ calves.”
Mr Orpin, with NMR vet Karen Bond and PAN Livestock’s James Hanks, will be sharing these developments with vets in Johne’s master classes, which will start this autumn, and encouraging more specific control measures to be implemented.
They will be promoting a new priority cull-cow report, developed by the Action Johne’s group, that’s now part of NMR’s HerdWise service.
“It ranks infected cows depending on their test result,” explains Karen Bond. “We classify infected cows with repeated test results above 30 as ‘red’ cows, but the range above this can be extensive with some cows having significantly higher test results and being further on in the progression of disease compared to others, says Dr Bond.
These cows, with high levels of antibodies to the Johne’s-causing bacteria Mycobacterium Avium subspecies Paratuberculosis (MAP), present more of a risk of transmission, and the infection will have a much greater impact on their performance.
Cows with two consecutive results above 60 and/or one result above 100 are ‘losing control’ of the disease and are likely to be shedding large amounts of MAP. “They are the highest-risk animals in the herd and should be prioritised for culling,” says Dr Bond.
Mr Orpin wants to see vets use these more detailed reports with their clients as part of their actions. “Control can be improved by culling the right cows at the right time,” he adds.
“We need to dismiss the idea that all infected cows classified ‘red’ need to be culled immediately, as this isn’t practical or feasible on all units,” he says. “It’s a control mechanism that has been encouraged by some retailers, but it does not solve herd infection single-handedly. The infection needs to be taken out at the source. Culling is only part of the solution.”
New data looking at the KPIs of 2,000 HerdWise herds demonstrates the economic importance of Johne’s. “We know that infected cows are more likely to have performance setbacks,” explains Dr Bond.
“Cows that repeatedly test positive for Johne’s, classified as J5 ‘red’ cows, have 305-day milk yields of 800 litres less than ‘green’ J0 cows that consistently test negative. “Based on current milk prices, this could be between £360 and £400 in lost milk income. And this is straight off the bottom line as it costs the same to keep a highly infected Johne’s cow as it does a healthy ‘clean’ cow,” she adds.
Herds with high levels of Johne’s-infected cows also have higher average herd somatic cell counts, and more fertility problems. “As the prevalence of Johne’s infection increases, so does herd somatic cell count. The relationship is linear, so even the performance of those herds with lower levels of Johne’s infection is being compromised.”
The high cost and lower efficiency seen in herds with Johne’s infection should encourage producers to seek better control.
“We have some good evidence coming through on the Tracker reports that shows that herds can move from a high level of infection, where between 10% and 20% of cows test positive, to a low level, with less than 3% of ‘test positive’ cows, when all the risk factors are controlled and a robust plan is in place,” adds Mr Orpin. “The aim for every producer is to have a herd with no priority culls and less than 2% of ‘test positive’ cows. The disease is well controlled at this stage.”