Bovine Tuberculosis

An overlook at tuberculosis in dairy livestock, including causes, symptoms, transmission, history and prevention.

| December/January 1992

  • bovine tuberculosis - vet examination
    If you buy a cow or goat for family milk, have your veterinarian test the animal for tuberculosis.
  • bovine tuberculosis - myobacterium tuberculosis cells
    Mycobacterium tuberculosis, magnified 380 times.
  • bovine tuberculosis - pouring milk
    In the early 1900s, there were so many infected cattle that many humans contracted TB from drinking unpasteurized milk.

  • bovine tuberculosis - vet examination
  • bovine tuberculosis - myobacterium tuberculosis cells
  • bovine tuberculosis - pouring milk
The forest mixture of hard and soft maples, oak, ash, and pine that we have here in the Northeast produces a most beautiful fall foliage. Yet, until one October a few years ago, I felt that nothing in this brilliant display of beauty could compare to the soft, golden yellow of the aspen-covered slopes of western United States and Canada. 

My wife and I were traveling a seasonal mountain road along the ridge that separates Massachusetts and Connecticut from New York State when we came across a rich, golden foliage. The trees that held these beautiful leaves were second growth American Chestnut. Although they once covered our hills and ridges, they died in the 1920s due to a blight; the present growth is from still live roots of these apparently long-dead trees. They will grow to about 20 feet, and then, like their parents, they will die back with only the roots surviving.  

Although some foresters tell us it will never happen, those of us who knew the value of its edible nut and durable wood of many uses keep hoping that one of these new growth trees will be blight-resistant and reproduce—that the species will flourish again. We know that other living organisms develop resistant strains, such as bacteria becoming resistant to antibiotics, or the Brahma cattle becoming resistant to certain tropical diseases. Conversely, animals (including humans) lose resistance to certain diseases if they are not exposed to it for several generations. When they are exposed, they may die from a disease which would have caused only a mild illness in their grandparents.  

There are many examples in recent history of diseases once rampant in animals and humans that have practically disappeared and then suddenly reappeared. One disease that has suddenly reappeared after years of being virtually unknown is tuberculosis, once commonly referred to as "TB."

With all the publicity about its resurgence, we have recently received many questions about tuberculosis. Since there is no known immunization against the disease, the best way to protect ourselves and our livestock from it is to learn all we can about what causes it, what its symptoms are, and, most important, how it is spread.

Tuberculosis, which affects most warm-blooded animals, was thought to be almost nonexistent in the United States and Canada 25 years ago. Any veterinarian of my generation with knowledge and experience of TB could write enough to fill this magazine, which would no doubt bore most of you. Instead, I offer a little background and a discussion of what you, as a livestock owner, need to know in order to protect yourself and your animals from the resurgence of this disease.

Here's What's Causing TB

There are several strains of TB, caused by a bacteria of the genus Mycobacterium tuberculosis, the human form. The most common strains in barnyard animals are M bovis and Mavium, which are found in cattle and birds, respectively. The human strain and the bovine strain are the most closely related. Literature often refers to the organism as being "acid fast," which means that when the material containing the organism is stained with a red dye and washed with a bleaching acid, the organism retains the red color. This makes it more visible under a microscope.

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