The last herd test before drying off is a great time to test your herd for Johne’s Disease – an infection that causes millions of dollars of lost production annually nationwide.
Johne’s Disease is an infection caused by the bacteria Mycobacterium avium subspecies paratuberculosis (MAP) that affects the small intestine of cattle. DairyNZ estimates the cost to be between $44-80 million in lost production annually.
Johne’s Disease is common worldwide, including many New Zealand farms. Calves are at risk of being infected so testing herds before calving is crucial.
Co-op Programme Manager (Veterinary) Sue Campbell recommends farmers do an annual whole herd Johne’s milk test at the time they are making culling decisions.
“For most this is February/March, to enable the identification of Johne’s positive cows before calving – reducing the risk of transmission to the next generation. Overseas work shows calf-to-calf spread occurs, reinforcing how important the timing of culling is.”
"Johne’s can be transmitted from dam to daughter (4-40% of the time, in-utero), through colostrum, milk and faecal spread either directly (animal to animal) or through environmental contamination," says Sue.
“Having all lactating cows present at the Johne’s herd test is critical, even missing a few cows who are shedding means that the disease could persist for another season through pooled colostrum. Getting subsequent bloods of any cows with missed testing for any reason, including cows with ‘reject’ milk herd test samples is essential.”
What do the results mean?
Work with your vet to develop a whole farm approach to Johne’s control.
“Testing and culling alone will not be effective in reducing the long-term incidence of Johne’s disease. To get the best outcome, decisions need to be made using the data and reflecting the farms Johne’s control goals,” Sue says.
You may have Johne’s results reported as:
- Not detected: No immune response was detected – it is likely she is free of Johne’s disease (but there is no guarantee).
- Suspect: A low level of immune response is detected – approximately 80% of the time when that cow is subsequently blood tested for Johne’s, she will test positive again.
- Positive: A high level of immune response was detected – it's highly correlated that when that cow is subsequently blood tested for Johne’s, she will test positive again.
- High Positive: A very high level of immune response was detected – it's very highly correlated that when that cow is subsequently blood tested for Johne’s she will test positive again.
What do I do with my Johne’s results?
Work with your vet to make a plan – they know your farm and how to reduce transmission. It’s likely from the test results they will recommend:
- Re-testing cows that tested 'suspect'
- Cull the cows that tested ‘high positive’ and ‘positive’ ASAP
- Only pool colostrum/milk for calves from cows that tested ‘negative’
- Reviewing breeding records to identify previous daughters of positive cows who are at higher risk of testing positive.
If you can’t cull all cows that tested ‘high positive’ or ‘positive’, then your vet may recommend you:
- Permanently identify all test high positive/positive cows and manage as a separate herd
- Don’t keep any of the calves as replacements; bobby all these calves
- Don’t keep colostrum from these cows
- Cull these cows as soon as you are able
- Develop a whole farm plan to reduce faecal contamination and disease spread.
Remember, annual testing needs to be undertaken without a gap for a period of 5+ years to get best results. For real data-driven decision making, have a look back through breeding records/ genomics to identify daughters of test positive cows for mating and culling decision making.
For more information contact your local vet or Farm Source team member.