When Ensiling Grasses, Don’t Forget the Risk of Listeria

Stan Smith, PA, OSU Extension, Fairfield County

In a recent memo to OSU Extension Beef Team members, Ohio Beef Industry Center coordinator Francis Fluharty reminded us about the potential for Listeria issues to surface. Fluharty says that if you are making baleage, and it’s too wet to make a round bale, but too dry to make a good baleage bale, you stand an increased risk of having a poor fermentation, resulting in mold. Those are the conditions where Listeria monocytogenes functions best. The result is the risk of getting Listeria (circling disease) next winter in the animals being fed the poorly fermented forage. Fluharty reminds that once you see the symptoms, it’s typically too late for the cow!

In the article below, Dr. Shulaw details why and how Listeria can become a risk for livestock being fed improperly ensiled crops.

Listeria a Concern in Ensiled CropsWilliam P. Shulaw DVM MS, OSU Extension Veterinarian, Beef/Sheep

Listeria monocytogenes infections are relatively common in sheep, goat and cattle production systems. These bacteria are frequently shed in the manure of apparently normal animals that serve as chronic carriers. The bacteria usually find their way into the ensiled material by soil or manure contamination of the forage prior to, or during, the ensiling process. One common way this happens is when tractors that are used for other animal management operations are used to pack forage in a bunker silo.

Ideally, ensiled material should reach a pH of 4.5 or so after fermentation. Listeria can continue to grow at a pH above 5-5.5. If the material is chopped coarsely, or inadequately packed and sealed, the fermentation process may not reach the desired low pH. In addition, there may be pockets that did not reach the proper acidity in otherwise acceptable forage. Listeria can grow in these pockets. Reaching proper acid levels is usually easier with corn silage than grass or legume silages. Silage is often incriminated in animal infections, but not all infections can be traced to silage feeding.

Animals that consume the bacteria may develop intestinal infections that cause no disease but which result in chronic shedding of the bacteria in the manure. This helps ensure survival of the bacteria on the farm. In some animals, the mammary gland is chronically infected. Dairy cows have been known to shed the organism in the milk for months. Mammary infection in other species is possible also. The bacteria may gain access to the body through the tonsil, or abrasions of the mouth, and travel up the cranial nerves to the brain. When this happens, small abscesses in the brain occur and the animal develops the classic signs of “circling disease” with incoordination, circling to one side, and paralysis of the lips, ear and eyelids on the affected side. Most of these animals die unless treatment is begun very early.

Listeria can also cause abortions. This is most common in sheep and goats and may be more common than the brain infections in those species. The bacteria are shed in the aborted fetus, placenta, and discharges. Occasionally, listeria may cause outbreaks where both abortions and the signs of brain infection occur (in different animals), but this is not common.

Unfortunately, these bacteria can also cause infections in people, especially pregnant women, elderly people, and the immunocompromised. Unpasteurized milk, or inadequately pasteurized milk, and contact with aborted fetuses or discharges are potential natural sources of the bacteria for people. Producers should practice good personal hygiene, especially around aborting animals, and should not consume unpasteurized dairy products.

There is no vaccine and treatments for infected animals are usually only moderately successful. The bottom line for effective prevention of losses in animals is to practice good sanitation, make the best quality silage possible ensuring adequately low pH for proper preservation, and with baleage, be sure that the plastic remains sealed.