WOOSTER, Ohio – Dairy farmers should be on the lookout for poor quality silage because it can lead to listeriosis, an illness also known as silage disease and circling disease.
Listeriosis is caused by the bacterium Listeria monocytogenes, which is often found on plants, in the soil and in natural waterways. It is also frequently isolated from the manure of cows, pigs, sheep, goats, chickens, horses, dogs, cats and even people.
No signs. Animals and humans may carry the bacterium without any outward signs. An estimated 1,500 to 2,500 Americans become ill due to Listeria each year.
The illness can be fatal.
While exposure to a small number of the organisms doesn’t appear to be dangerous to animals, using feed that has been inadequately ensiled and does not reach an acidic pH of less than five can pose a problem, according to Jeffrey LeJeune, a veterinarian and microbiologist with Ohio State University Extension and the Ohio Agricultural Research and Development Center.
Under these conditions, Listeria naturally present on the feedstuffs slowly multiply during storage, resulting in a large number of organisms accumulating in feed by late winter and early spring. Most outbreaks of listeriosis in animals occur during this time of year.
Animals most at risk of becoming ill from exposure to Listeria are those that are stressed due to other conditions, such as pregnancy, infections, or mouth injuries from rough feeds or lost or cutting teeth, LeJeune said.
Greater risk. Wide temperature fluctuations also put animals at risk of actually becoming sick, as opposed to remaining healthy and simply shedding the organism in their feces, he added.
Listeria infection can result in circling disease, in which affected animals walk in circles, but more often than not it presents itself as the cause of a late-term abortion outbreak in a herd of cattle, affecting 5 percent to 10 percent of the herd over a two-month period.
Listeria can also cause mastitis, but that’s not very common.
Veterinarians usually diagnose Listeria by testing a dead animal’s diseased tissues or examining the brain and placenta for Listeria-related changes.
Antibiotics. “If you suspect listeriosis in your herd, it is important to save samples from dead animals for veterinary inspection and confirmation” LeJeune said. “Antibiotics are usually effective during the early stages of disease.”
If the veterinarian identifies animal feed as the source of the problem, the contaminated silage must stop being used. However, prevention is the best medicine.
“Take precautions when silage is chopped and packed and make sure it reaches the appropriate pH conditions. That will limit the likelihood of Listeria growing in the feed,” LeJeune’s said.
For information about Listeria and animal health, ask your veterinarian or contact LeJeune’s laboratory in Wooster at 330-263-3619 or firstname.lastname@example.org.
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