I want you all to think about your herd and whether you can ever remember having a bull or cow that started losing weight in spite of a great appetite. Did this bull or cow eventually get diarrhea, perhaps even bottle jaw, and die? If so, then you may have a first-hand experience with Johne’s disease.
Johne's (pronounced "Yo-nees") disease is a contagious bacterial disease of the intestinal tract. The bacteria which causes Johne’s disease is called Mycobacterium paratuberculosis (M. paratuberculosis). The disease can be confusing to understand, and there are many variables to consider, but for the sake of simplicity, it boils down to this:
- The bacteria are ingested by a young calf.
- It sets up shop in the calf’s small intestine, but grows very, very slowly.
- It eventually (2 or more years later) takes over the normal architecture of the intestinal wall and the animal begins not to absorb its nutrition very well and loses weight in spite of a great appetite.
- The organism continues to grow, making it even more difficult to absorb nutrients leading to loose stools and weight loss.
- The intestines essentially fail to do their job of absorbing food and the animal gets emaciated and dies.
During the growth of this organism in the intestinal tract, some of the bacteria begin to leave the intestinal wall and get a free ride to the outside in the animal’s feces and land on the ground with the rest of the fecal matter. Sometimes, before clinical signs (i.e. weight loss and diarrhea), there are still enough bacteria in the intestine to be released into the feces in this matter and these animals are known as “shedders.” This means that this animal sometimes ‘sheds’ the organism—and sometimes doesn’t—because the bacteria are still growing very slowly and sometimes there’s just not enough to leave home (the small intestine) for the free ride to the outside (i.e. ‘intermittent shedding’). Some cattle ‘shed’ bacteria 15-18 months prior to development of clinical signs. This becomes important when we talk about testing animals for this disease.
As the bacteria proliferate (perhaps even 10 years from the time the calf ingested it!) and the animal’s intestines become more invaded, the bacteria hops on the free ride more frequently and once the animal has diarrhea, almost all of the feces contains some bacteria in it. All of the animals exposed to this feces may ingest the bacteria and become infected.
Calves are the most susceptible due to the integrity of their immune system. Consequently, a mama cow with Johne’s disease who is shedding a lot of bacteria in her feces is going to infect her calf. Some cows shed it in their milk, as well. She may also infect other calves in the same pasture. If she is shedding lots and lots of bacteria, she may even infect some of the weanlings or adults! But, it still takes a long time for the organism to grow, and the more bacteria the animal is exposed to the faster the animal will progress through the stages of disease. |
|
Testing for Johne’s can also be complicated. There is a blood test that is about 80% accurate. But the definitive way to diagnose the disease is by taking a sample of the feces and culturing it. Since the bacteria take a long time to grow in the animal, it makes sense that it also takes a long time to grow in the lab. It takes up to four months from the time the feces is cultured to know whether or not the animal has Johne’s. If the culture is positive, then the animal DEFINITELY has the disease. If the culture is negative, the animal still may have Johne’s, but the bacteria hadn’t hopped on that portion of the feces obtained and therefore there was no growth. There is a new test available, as well, that looks at the DNA of the organism in the feces. This gets results much faster than the traditional fecal culture but not as sensitive (meaning if there is only a small amount in the feces it may not detect it). The fecal culture is still considered the ‘gold standard’.
One recommendation is to have your animals blood tested for the disease each year and do fecal cultures on the positive ones. With expensive bucking stock, you may just choose to separate the positive ones to a different herd or remove the calf immediately after birth. The best way to prevent valuable animals from contracting the disease is to cull the ones that are confirmed positive on a fecal test.
Over the past couple of years, we have seen a few very good bucking bulls presented to our clinic with Johne’s disease. There is no cure for this disease and all of these animals eventually died.
Lee Murphy’s ABBI Classic bull“M3 River Water” was purchased as a calf. He eventually began to lose weight despite what he was fed. We were able to preserve some semen from him, but Mr. Murphy decided to humanely euthanize him due to the detrimental effect he may have on his stock if they were exposed to him at this stage. Once faced with this disease, no matter how difficult, the best decision is to cull the affected animals. Some tactics for avoiding infection in your herd include:
- Never use a dairy cow as a nurse cow.
- Never use dairy cow colostrum for orphan calves.
- Never use dairy culls as ET recipients.
- Do everything possible to avoid buying infected cattle
The best thing to do is to speak with your veterinarian concerning testing and prevention of this disease in your herd. There is nothing more heartbreaking than watching one of these great athletes waste away from this disease. |
