Test and cull is not the answer to Johne’s control, according to vet, Ingrid Bijker, West Ridge Vets. “The key to controlling Johne’s is to prevent the cycle of infection by managing positive cows effectively,” she says.
And milk recordings can prove an effective tool for monitoring and controlling disease within the herd.
“Over the years, we have had phases of cows showing signs of Johne’s through reduced fertility and high cell counts, so about three years ago we began blood testing cows once a year at drying off.”
However, testing once a year reduces the sensitivity of the test, says Ms Bijker. “Because Johne’s antibodies naturally fluctuate throughout the year, testing once a year only has about 50% sensitivity, so although an animal may come back negative, she could end up positive at a later date.”
However, using Herdwise means cows can be tested four times a year, increasing the sensitivity of the test to 90%.
This method of testing is not only more accurate, but is also cheaper, says Mr Jefferson. “Four milk tests cost the equivalent of one blood test. And we are simply using what we already had in place by using milk recordings more effectively.”
The report, which is accessible through Herd Companion, also takes into account drops in milk yield which can be a precursor to clinical signs of Johne’s, explains Ms Bijker.
Results are easy to interpret, says Mr Jefferson. “Cows are clearly identified as red, yellow or green – red being cows that have repeated positive Johne’s tests, yellow for cows which have had a positive result and green for Johne’s negative animals.
Mr Jefferson uses this information to make sure Johne’s positive cows are clearly identifiable within the herd.
“All red and yellow cows are tagged with a red ear tag, so they can easily be picked out within the herd.
“This means, as soon as they come to calve, everyone knows they have to be split off to calve in a separate pen.”
The key to controlling Johne’s spread is to prevent calves from becoming infected, Ms Bijker says. “Calves are most susceptible to Johnes’s, with 80% of infection occurring within the first month of calving. After one year old, cows are less susceptible with older cows difficult to infect,” she explains.
Infected cows shed Johne’s during times of stress, such as calving, so isolating these animals, removing calves as soon as they “hit the deck” and cleaning pens between cows is essential to minimise the risk of disease spread from faeces or through the milk.
“By doing this, eventually, all infected cows will die out and any calves coming through will be healthy.”
For 90% of calves we do manage to remove calves before they suck, but there is always a proportion that calve in the night, says Mr Jefferson.
“When a Johne’s cow calves in the night, we will tag the heifer calf with a red tag so we know she is a potential carrier.
“Calves born to Johne’s cows will receive “clean” colostrum or freeze dried colostrum to reduce the risk of disease spread.”
However, there is always a 10% risk of Johne’s transmission from cow to the unborn calf, says Ms Bijker. To reduce this risk, Otter Farm has started putting all Johne’s cows to beef bulls, so offspring are not entering the herd.
The red tag also allows cows to be selected out of the herd. “Any cow showing clinical signs of the disease will be culled. For example, a red cow with high cell counts is more likely to be culled out of the herd, because she could be showing the signs of Johne’s.”
But culling as a Johne’s control strategy is not the answer. “Culling is an extremely expensive option and also does not tackle the disease,” says Ms Bijker.
“By testing and culling, you are not stopping the infection rate, so infection will remain the same in the herd. By testing and managing infected cows, Johne’s will eventually be eliminated in the herd.”