An analysis of nine hundred x 30 cow screens performed over a 6 month period has shown that one or more positive results were found in just under 70% of herds tested.
Studies in America have revealed that Johne’s infected animals:
- Gave on average 4000 litres less milk over their lifetime
- Were 5 times more likely to be lame
- Were 2 times more likely to get mastitis/high SCCs
- Were 1.8 times more likely to develop digestive disorders
So this is a major disease that can have a big impact on farm profitability which needs to be considered.
Johne’s is a chronic intestinal disease which will cause scours and loss of condition, and badly infected animals can die if not culled before.
Most animals become infected within the first 24 hours of life, but as the illness is slow to progress they may show no signs of clinical illness until they are mature milking cows.
Johne’s infected animals are more likely to have lower milk yields, higher SCCs, more mastitis or more lameness, so can often be culled for these reasons without being aware of the underlying illness.
Where does Johne’s come from?
Johne’s can enter your herd by:
- Buying in infected cattle. This is the most likely source of infection from either cows, heifers or bulls.
- Imported slurry. Johne’s can survive in slurry for up to 12 months. So be careful who you import slurry from, especially if it is going onto grazing land.
- Watercourses. It is possible to get Johne’s from infected herds upstream if they have access to the watercourse, or they have slurry runoff from their ground.
How does it spread?
Johne’s infected animals shed vast numbers of the bacteria, so their manure is the biggest source of spread.
Contamination of the calving environment, cows with dirty teats and dirty calf feeding equipment are all bad news.
Bacteria are also shed into the milk so feeding contaminated milk and colostrum are also a main source of spread.
There is a minor risk of the infection being spread from cow to calf before the calf is born, but this is thought to be very small.
How does the disease progress?
Initially the animal’s immune system can control the bacteria and there will be little or no antibodies produced, so any test will come back negative. This period can last for up to 3 years.
After this, there is a period when the bacteria begin to multiply and the cow will start to produce antibodies. The pattern of antibody production can fluctuate up and down as the cow tries to fight the disease, so she may test high at one reading then low at the next. During this phase the animal will normally start to show signs of production problems. It is thought that stress events may trigger these peaks in antibody production.
Then the cow loses control of the disease, antibody levels will increasingly rise and the cow will show classic signs of the disease – weight loss, scours. At this stage the cows is very infectious to the rest of the herd.
How do I find out if my herd is affected?
Bulk milk testing for Johne’s is not recommended for indicating prevalence within a herd as the bulk result can be low even if around 10% of the herd are badly affected.
The starting point is to do a targeted 30 cow screen test to assess if Johne’s is present.
Cows should be selected which are:
- Between 3-7 years old
- Repeat high SCC or mastitis cows
- Persistent lame cows
- Cows with unexplained falling milk yields
- Poor doers
These tests can be done quarterly through NMR’s Herd Tracker service and can be helpful if you want to routinely monitor to ensure you do not have the disease in your herd.
If Johne’s is identified in your herd then you can use NMR’s Herdwise service which monitors all the milking cows in the herd on a quarterly basis.
Your normal monthly milk recording samples are used so there is no extra work involved in sampling.
The cows are categorised by colour to help you determine their risk status:
- Red cows are likely to be shedding high numbers of the bacteria, show clinical signs and be highly infectious
- Amber cows are likely to shed bacteria intermittently and pose a risk of spreading the disease
- Green cows have never had a positive test and are very unlikely to be infectious
Cows are also assigned to an infection group on a scale of 0 – 5, with 0 being least risk and 5 being highest. Cows coded as ‘Green’ can be classed as J0 - J2 cows which means they have had 1 positive test (and therefore have the disease) but it is in the very early stages and is likely to pose little risk to other animals.
‘Amber’ cows are coded as J3 – J4 and these cows are likely to be in the subclinical phase of the disease and are likely to be infectious and should be managed as such.
‘Red’ cows are coded as J5 and are likely to be shedding large quantities of the bacteria. These are your highest risk cows and should be managed under the tightest controls.
What do I do with infected cows to prevent/minimise the risk of disease spread?
Ideally treat all cows that have had one positive test as at risk. If not possible, treat all red and amber cows as Johne’s risk animals if farm facilities allow you to do this. If not the more you can do the better.
Identify and mark these high risk cows with neck collars/red tags/leg bands/tail tapes etc to ensure all staff know who the Johne’s cows are.
Calve these animals in individual calving pens and snatch the calf away immediately. Clean and disinfect the pen thoroughly between each animal.
Bear in mind that if you have these cows in your transition yard with the others prior to calving, they will be shedding bacteria onto the bed. If your non Johne’s cow then subsequently calves down here, the calf will be at risk of picking up the infection from the bed. If at all possible keep Johne’s cows in a separate pen.
Do not feed colostrum or waste milk from these animals to calves. Some farmers are pasteurising milk/colostrum to reduce the risk of infection, but we would keep all Johne’s cows milk away from youngstock.
Whilst Johne’s positive cows stay in your herd ensure you serve them to beef, and as soon as you see production being affected cull them.
Cull Johne’s positive cows as soon as your replacement rate allows, and breed sufficient replacements to accelerate culling for this damaging disease.
If you are buying in animals investigate what testing has been done for Johne’s and what management plan they have in place to minimize the spread of this disease, if any. Once the animals are on your farm treat them as high risk until you have testing information at hand to categorise them properly.
To discuss testing and control methods for your farm from a practical view point please contact the office 01666 817278.