Food Safety

Published on March 6th, 2008 | by Meredith Melnick

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More Bad Cow News: Johne’s Disease Linked to Crohn’s Disease

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bottle_of_milk.jpgI guess Thursday is Bad Cow Day. Sorry cows! I love your sweet, cud-chewing faces, but your owners have issues!

According to the Humane Society, 17% of the U.S. beef supply comes from spent dairy cows. These cows no longer produce financially viable quantities of milk and are sold at steep discount to slaughterhouses. In fact, prices for dairy cows can be as little as one-tenth the price of a well-fed beef steer on the meat market. This partially has to do with net meat gain: the dairy cow is bred for optimum lactation, not muscle mass. The price differential also has to do with condition: the dairy cows tend to be older and more feeble, depleted of calcium and afflicted with a multitude of bacterial infections, the result of sedentary, unifunctional lives.

Because dairy cows stand all day, the damp manure and hay contribute to bacterial growth on the hooves, known as foot rot. The constant handling of their udders can cause mastisis – another bacterial infection. Still another common malady is Johne’s disease – a wasting illness that comes from the same bacteria family – Mycobacterium - as tuberculosis and leprosy. Johne’s disease, like foot rot and mastisis, is usually the result of improper contact with manure: cows contract it by eating food and drinking water that is contaminated with manure in which the bacteria is present. The infection is highly contagious and spreads quickly as up to 500 billion organisms can be shed through fecal movement by a single infected animal in one day.

The bacteria is resistant to disinfectants and harsh environmental conditions and does not trigger a response from the immune system, which is the most common way the body resists infections. This means that young cows – those with the most robust immune systems – do not have a defense against Johne’s disease. Additionally, most cows with Johne’s disease do not have any symptoms or signs of infection. Those that do have such signs (which include weight loss and severe diarrhea) usually develop them later in life.

Alberta’s Agricultural Ministry estimates that 35% of dairy cows that suffer from Johne’s disease release the bacteria through their milk. And, because of the bacteria’s hardiness in harsh environments, it very often survives the pasteurization process and enters the commercial milk supply. A 2004 study by Dr. Jay Ellingson at the Marshfield Clinic Laboratories in Wisconsin, found that 2.8% of his 702 samples from top milk producing states (California, Minnesota and Wisconsin) contained Johne’s Disease bacteria that was alive and capable of multiplying.

While some farmers, veterinarians and doctors have long suspected a link between this bovine illness and intestinal ailments in humans, it hasn’t been until recently that a connection was established. The data has focused on the correlation between Johne’s and on particular human ailment, Crohn’s Disease. Crohn’s Disease is a chronic inflammatory intestinal disease that causes wasting in humans. According to the Paratuberculosis Awareness and Research Association, over half a million Americans suffer from it and the rate of diagnosis is steadily increasing, particularly in young people. An estimated 20,000 Americans are diagnosed each year.

Recent epidemiological studies found DNA belonging to the Johne’s Disease bacteria – Mycobacterium avium paratuberculosis – in Crohn’s tissue, which is obviously a strong indication of association. The study isn’t considered scientifically conclusive, though, because researchers haven’t yet determined a causal role for Johne’s. For an excellent rundown of all current scientific data on the connection, read this article.

Studies have only been conducted on milk, but the bacteria is present in blood serum and thus can potentially spread through meat consumption as well. When discount dairy cows are sold at the meat market, the introduction of Johne’s Disease bacteria could be an additional concern. Hopefully, with further research, a more confirmative correlation can be drawn and we can begin to eradicate Johne’s Disease from our cattle and Crohn’s Disease among ourselves. In the meantime, more responsible and humane dairy farming practices such as isolating cow dung and manure from the food and water supply (not to mention the watershed! what about poor wild ruminants like deer and elk?) would be a good start. And finally, let’s stop selling sick cows on the meat market. We deserve better than downer burgers.

While there is a vaccination available for livestock in the U.S., Europe and New Zealand, there are concerns that it disrupts tuberculosis testing in farm animals and that it causes severe rejection reactions in some animals and humans.


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About the Author

I am a big fan of food. I am not a big fan of endocrine disrupting or carcinogenic compounds in my food. I will probably write a lot about that here.



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