Circling Cow Disease

By Dr Charlie Blackwood

Silage is making up a high percentage of the diet for many of our cows at the moment. Occassionally we do see diseases probably from bugs which live in silage.

Listeriosis is a disease caused by a bacteria called Listeria monocytogenes. It is found all around the world, but its ability to reproduce and grow well in temperatures down to 4*C makes it more frequently seen in cooler climates, such as Southern Victoria. Listeria monocytogenes is an aerobic bacteria, i.e. it needs oxygen to grow, and it particularly likes the less acidic pH of spoiled silage. This means that the longer your silage has been sitting around, the greater the risk of it no longer being sealed and thus starting to spoil.

In fresh silage with a pH of less than 5.4 the bacteria only survives for 1-2 weeks, where as in soil and/or rotting vegetation the bacteria may survive for up to 2 years. In fact even though we usually blame silage, the bug may come from rotting vegetation more often.

Ingestion of large numbers of Listeria monocytogenes can cause both septicaemia (infection in the blood stream), more commonly seen in young stock, and abortion in cows, but the most frequently diagnosed form of the disease is encephalitis, i.e. when it affects the brain. This will cause the affected animal to first lose its appetite, seem disorientated or sometimes just stand with its head in a corner or up against a solid object.

This may occur as soon as 24-48 hrs after ingestion or may take 10 days to develop. However, once signs of disease have started, the affected animal generally deteriorates quite rapidly, over a course of 2-3 days and without treatment, almost invariably dies. As the disease progresses, the animal may start to show signs of facial paralysis; Drooling, tongue hanging out, one ear hanging down, slow or absent blink response when touched around the eye or even blindness.

In the terminal stages of the disease the animal may start to circle continuously in one direction, may hold its head to one side or may even lie down and appear to be trying to role over, sometimes with involuntary paddling movements of the legs.

Treatment is possible if started early, but unfortunately in order to get the drugs to cross into the brain, are needed at much higher doses and for a much longer period than what you would use to treat an infection somewhere else, in the cow. When treated early enough, generally before circling starts, and with high enough doses of the correct antibiotics, you can expect recovery in about 50% of cases.

So how do I avoid my cows getting the disease in the first place?

The key there, would have to be to make sure you are only feeding good quality silage that has just been opened, silage sitting out over night, is enough to grow lots of L. monocytogenes. If you do have some old silage that you would like to use, make sure that it has been handled and stored properly and discard any bales that have holes in them or where the silage looks discoloured or smells different. If in doubt, don’t hesitate to call your vet.

silage