Dairy farmers should be on the lookout for poor quality silage, say animal health experts. It can lead to listeriosis, also known as "silage disease" because of its strong association with poor quality silage.

"It is also sometimes called 'circling disease,' since affected animals sometimes walk in circles," said Jeffrey LeJeune, a veterinarian and microbiologist with Ohio State University Extension and the Ohio Agricultural Research and DevelopmentCenter.

Listeriosis is caused by the bacterium Listeria monocytogenes, which is often found on plants, in the soil, in natural waterways, and also is frequently isolated from the manure of cows, pigs, sheep, goats, chickens, horses, dogs, cats and even people. 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.

"For the most part, exposure to a small number of the organisms doesn't appear to be dangerous to animals," LeJeune said.

"However, using feed that has been inadequately ensiled and does not reach an acidic pH of less than 5 can pose a problem,” he adds. “Under these conditions, Listeria naturally present on the feedstuffs can 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, other infections, or mouth injuries from rough feeds or lost or cutting teeth, LeJeune said. 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, LeJeune said.

Listeria infection can result in the classic "circling disease," but more often than not presents itself as a 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 also sometimes causes mastitis, "but that's not very common," LeJeune said.

Veterinarians usually diagnose Listeria by testing a dead animal's diseased tissues or examining the brain and placenta for Listeria-related changes. "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.

"But prevention is by far the best medicine," LeJeune added. "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."
For more information about Listeria and animal health, ask your veterinarian or contact LeJeune's laboratory in Wooster at (330) 263-3619 or lejeune.3@osu.edu.

Ohio StateUniversity