A goat suffering listeriosis associated with silage feeding. The head tilt indicates an infection on one side of the brain. Photograph courtesy of Dr Bob Templeton, district veterinarian, South East LHPA, based at Braidwood
TWICE over the last month I have teamed up with veterinarians from the Lithgow Veterinary Hospital to investigate goats that have become sick then died on commercial goat farms.
On one farm, the owners observed that a couple of mature goats became dull before separating from the mob then tending to walk or fall to one side. Prior to death, they collapsed on one side. On the other farm, the owner found a single wether goat lying semi-conscious and paddling before death.
The symptoms shown by the goats indicated a developing brain disease. We therefore submitted samples of the brain and other tissues to the laboratory with the aim of confirming a diagnosis.
The pathologist reported to us that on both farms the goats died of a bacterial brain infection caused by listeria.
You may have heard of this bacterium. Not only does it cause brain infections in sheep, goats and occasionally cattle but it can also cause pregnant livestock and women to abort. So this group of bacteria are important both in veterinary and human medicine.
Several of my colleagues reported outbreaks of listerial abortion in sheep last year and I am aware of at least one outbreak this year. In the winter of 2011, up to 10 per cent of ewes from Monteagle to Uranquinty aborted their lambs, from two to four weeks before they were due.
Previously, other local veterinarians have described listeria causing brain infections and death in ewes fed silage.
Scientists have found this bacterium is widespread in the environment, from soil to water to the walls of buildings to sewage sludge. It can also be found in mammals, birds, crustaceans and insects and within the digestive tracts of healthy people.
In most cases, the disease does not trouble animals with a healthy immune system. However, pregnant ewes and goats seem to be susceptible.
The textbooks tell us that listeria grow well in spoilt or contaminated silage. High-risk animals such as pregnant sheep and goats are therefore susceptible to either brain disease or to abortions if fed silage. Cattle and other classes of sheep seem much less susceptible.
In these recent cases of brain disease in goats near Lithgow and abortions in ewes last winter, silage was not on the menu. However, in some instances farmers had slashed rank vegetation. We suspect this slashed material, which had rotted with the above average rain, also favoured listeria.
Well-made silage is an effective and economical method of feeding livestock both for production and in a drought. However, goats and pregnant ewes risk developing listeriosis under some circumstances when fed silage. It also seems that rotting vegetation, especially if it has been mowed and left rotting in windrows, is a risk to sheep and, in the light of our recent experiences, goats.