Johnes Disease
What is Johnes?
Johnes disease is caused by a bacteria that invades the gut. This invasion damages the normal cells lining the gut making them irreparably 'leaky' and therefore less able to absorb nutrients. This reduction in ability to absorb nutrients means the cow will begin to loose weight and her production starts to drop. Over time more and more cells within the gut become infected and useless at their job. This is what leads to the development of the chronic scour we all associate with Johnes disease.
Transmission
Where do the bacteria come from?
Johnes is a tough disease to break the cycle of infection because animals are generally infected at birth, but show no symptoms until later in life, usually >2 years old. Once the bacteria are shed into the environment from an infected cow they are very resilient and in the right conditions can remain on pasture or in effluent for up to 12 months. The main routes of transmission are outlined below...
Dam to Calf Direct
Infection happens at birth. A cow with Johnes disease will be shedding the bacteria in her faeces. When the calf is born it is highly likely to ingest some faeces and thus the bacteria directly from the surrounding environment, as it stands up and starts to lick the cow.
Via Milk
Infected cows shed the bacteria directly into their milk and colostrum. Poor hygiene could also result in faecal contamination of the milk. Calves fed milk ingest the bacteria. When milk or colostrum is pooled, one infected cow is able to infect many calves.
In Utero
Around 25% of calves born to infected dams have been shown to be infected before they are even born with transmission occurring while the fetus is developing in the uterus.
Calf to Calf, Other Cows to Calves, Water, Bedding, Slurry spreading....
Faecal contamination is everywhere! Basically anything a calf ingests that has been contaminated with faeces from an infected cow or another infected calf can result in the calf picking up the infection. The risk declines as the calf gets older with 80% of infections thought to occur in the first month of life and biggest risk being the first few days.
Should I be Worried?
It is estimated around 70% of NZ farms have Johnes disease on the property and it can cause huge losses in terms of milk production and lost cows that loose condition and are unfit to be sent to the works. Estimates are it is costing the NZ dairy industry between $40-90 million/year in production losses.
Most of our farms have the odd cow we sample or are suspicious of every year but the true prevalence in your herd could be anywhere between 1-10% - sadly we won't know until we start to look. In herds with high levels of disease it is likely this is negatively affecting lots of things on your farm including; overall production, pregnancy rates and cell counts etc.
Testing
There are a few testing options now available, each with different pros and cons. We can advise you which would suit your herd best.
Effluent testing
Suitable for: Farms who have never had a case a of Johnes diagnosed and want to know if it is on farm. This is a new test from LIC that screens 4 samples of effluent for the presence of the bacteria
Good for: starting screening test - gives a yes no answer if Johnes is detected on the property
Less good for: doesn't help to find any of the positive cows, false negative results if positive cows do not end up contributing to the sample or are not shedding, false positives if sample contains effluent from animals that have now left the herd. Needs to be used on an ongoing basis with standalone results not used in isolation
Blood Testing
Suitable for: Individual cow screening of animals with suspicious clinical disease (scouring and weight loss)
Good for: Deciding whether to treat a sick animal or euthanase. Often used as a follow up to milk testing for positive animals. Also useful in beef herds or herds that don't routinely herd test.
Less good for: milk testing is cheaper and more convenient for whole herd screening
Milk testing
Suitable for: Screening the whole herd
Good for: Finding clinical and sub clinically infected animals - able to find some animals before they are showing clear signs of disease and thus enables management decisions to be made
Less good for: the test isn't sensitive enough to pick up all animals in the early stages of the disease and so ongoing monitoring - yearly/quarterly testing is advised
Control
There is no treatment for Johnes and cows displaying clinical signs of disease (scouring and weight loss) should be culled on welfare grounds. Ultimately if left, even with all the food in the world they will keep wasting away and eventually die.
There are numerous strategies for ongoing control of the disease within your herd depending on the level of Johnes you start with and your future goals. Because of the way it is transmitted to the young but remains 'dormant' for at least 2, if not more years in most cows, it is a very hard disease to eradicate altogether. However with the correct management, time and attention to detail it can be controlled down to almost unnoticeable herd levels with minimal losses. Each farms control plan will look different so it is important to get in touch with us if this is something you want to do for your herd.