Jonhe’s Disease

Written By: Nadine Wohlgemuth, DVM

Johne’s Disease (pronounced “yo-knees”) is a chronic, incurable, fatal infectious disease of cattle caused by the bacteria Mycobacterium paratuberculosis. One of the biggest problems with this disease is that it is difficult to detect and easily spread. There is no treatment and no cure.

Imagine this scenario: your best cow, the female that has won several ribbons in the show ring, is pregnant with her fourth calf. She never gained right after her last calf. You thought she wasn’t getting enough feed, so you gave her extra. She had on-again, off-again diarrhea but you thought that was feed related. Now, she has diarrhea all the time, despite a good appetite and no matter what you feed her she will not gain weight. Your veterinarian runs some tests and she comes back positive for Johne’s disease. What does this mean for this cow? For your whole herd? So let’s summarize this disease and what this diagnosis means.

How do cattle become infected? Calves are the most susceptible to the bacteria and are typically infected within the first 30 days, but can take up to 6 months. There are three major ways calves are infected: 1) calves are born positive – they became infected in-utero from a positive dam; 2) calves ingest the bacteria in colostrums or milk from a positive dam; 3) ingest the bacteria from manure coated teats, licking gates/corrals contaminated with infected manure; or ingesting contaminated feed and water. Feed and water become contaminated from the manure of infected cattle. Once a cow becomes infected, the bacterial lives in the small intestine. As the bacteria grows and damages the small intestine the animal begins to shed the bacteria in the feces. As an animal enters the final stages of Johne’s with chronic diarrhea she is shedding huge numbers of bacteria into the environment daily in her manure. Calves only need to ingest a small number of bacteria to become positive, whereas, mature cattle are less susceptible and must ingest higher bacterial numbers to become infected.

Why is Johne’s disease difficult to manage? There are three main reasons why Johne’s disease is difficult to manage: 1) cattle are infected at a very young age and do not show clinical signs of the disease typically for several years. On average it is 5-7 years after an animal is infected before they will show clinical signs. Initially after infection an animal will appear perfectly healthy, however, she will be shedding bacteria in her feces contaminating the environment and infecting herd mates. As the disease progresses clinical signs include: weight loss, on and off again watery diarrhea which progresses to chronic diarrhea all while the animal maintains a good appetite. Once the animal has chronic diarrhea the intestine has become so damaged it is no longer able to absorb nutrients and water properly. 2) The bacteria that causes’ Johne’s disease is very hardy and can survive in the environment for up to one year. 3) There are no perfect laboratory tests to diagnose animals infected with Johne’s disease.

How does Johne’s disease enter a farm? Johne’s disease almost always begins on a farm from the purchase of an animal already infected with the disease. There currently is no mandatory testing in Canada for producers selling breeding stock, however, if you are purchasing breeding stock, you can always inquire if there has been any positive diagnosis in the herd. The bacteria could also enter on shared machinery and equipment between farms’ that has been contaminated with infected manure. Biosecurity practices will definitely help in the prevention of infecting your farm.

What to do with positive show cow from the above scenario? CULL, CULL, CULL. The offspring from this cow must also be culled. All positive Johne’s cattle must be culled. There is no treatment. There is no cure. All positive animals do is infect the rest of your herd. If you have a positive diagnosis in your herd, your veterinarian will develop a plan and discuss the costs to eliminate this disease from your herd. Because of the nature of this disease and the limited abilities of the current diagnostic tests it can take 5-7 years to feel confident that your herd is free of Johne’s disease.