One disease that can severely impair the production of your beef or dairy herd is Johnes Disease. This disease is a bacterial infection that affects the intestinal linings of infected animals. Johnes is an illness that can be passed throughout the herd. There is no cure for Johnes Disease, and often Johnes infected animals have no outward signs of the illness. Johnes Disease can infect sheep, cattle, and goats. Also, some wild ruminants have been reported to be infected with Johnes Disease. However, Johnes is no threat to humans. The meat from a Johnes infected animal is still edible, and you can still sell infected cows as slaughter cows.
Johnes is caused by the bacteria Mycobacterium avium subspecies paratuberculosis. Scientists and biologists often abbreviate the bacteria with the acronym MAP. MAP is spread in the feces, saliva, and milk of an infected animal. However, in feces is where the most MAP bacteria are found.
Johnes disease usually starts in the first few weeks of an animal's life. Young animals with an open gut are very susceptible to infection by MAP. A calf can easily catch Johnes from its infected mother. Sometimes the colostrum of its mother is the culprit, and other times, the calf just simply eats manure-infected fodder or nurses on a manure-coated teat. Once ingested, the MAP bacteria make their way to the cow's intestinal tract. There, they attack the lining of the intestine, thickening it until the cow can't absorb nourishment from its food. Eventually, the cow becomes thinner and thinner and dies either from malnutrition or from complications due to the cow's poor condition.
Stages of Johnes
At first, Johnes infected cattle show no outward signs of the disease. In Stage 1 of the illness, cattle eat, drink, and reproduce as normal. Small amounts of MAP are shed in the animal's feces, and these tiny amounts may not be detected by certain fecal tests.
In Stage 2, Johnes infected cattle still eat well and look great. During this stage, the MAP bacteria begin to show up in many fecal tests, but many blood tests miss the diagnosis at this stage. Sometimes, the infected animals are at a higher risk for other illnesses, since the infection taxes the cow's immune system
In Stage 3 of Johnes, the cow begins to look bad. She can't keep good body condition despite a good appetite. The cow will start exhibiting more symptoms of the illness and she will suffer from diarrhea. Milk production will diminish as well. At this point, many tests will detect the disease.
In Stage 4, the cow is obviously very ill. She will suffer from extreme emaciation and become very weak. Her diarrhea will increase until it is nothing but a watery mess.
Silent Threat in the Herd
Young cows can be infected and carry the disease for years before progressing to stages 2-4. Cows in stage 2 don't show any outward signs of disease, and can be bought and sold with both the owner and the buyer being unaware of the disease.
Usually a stressful event like calving or illness causes the animal to progress to stage 3 of the disease. After several weeks at stage 3, the farmer often decides to sell the animal in a thin, weakened condition. If he hasn't had the vet out to work on the cow, he may never know that she was sick. The cow could have shed billions of MAP cells all over his farm and he would never know it.
For more information on Johnes, call your vet or visit these websites.