The mycotoxin sporidesmin is produced by Pithomyces chartarum, a fungus which grows particularly well in the base of decaying ryegrass Lolium perenne. Ingestion of sufficient amounts of the toxin leads to damage of the bile ducts of the liver.
The ensuing liver damage leads to an inability to excrete phylloerythrin (a breakdown product of plant chlorophyll). Increased levels of circulating phylloerythrin in the blood vessels passing close to the skin surface give rise to the classic lesions of photosensitivity that we see in ruminants.
We have had a number of clients through the clinic recently describing sheep with oedematous fluid-filled ears crusting at the edges and some with skin starting to peel off. These symptoms at this time of the year with stock on pasture are certainly cases of facial eczema. And no, it's not just sheep, we have had cases in cattle as well.
So, doctor, you say my animals have facial eczema - I'm pleased we now know what we're dealing with - could you please prescribe the solution to my problem? Well, no, not easily. We can certainly administer drugs that will minimise the symptoms if given early enough, we can offer sound advice on how to manage affected animals, but I'm afraid we are nowhere near clever enough to reverse the liver damage that is causing the problem. The animals that show clinical signs have certainly incurred liver damage, but so also have some of the rest of the herd/flock that do not show any overt signs. Despite the incredible regenerative powers of the liver, some of these animals will have a degree of damage which impacts on health and in turn production. This is the reason why facial eczema needs to be viewed as a disease to be prevented, not cured.
Luckily we have a number of options for protecting stock against facial eczema damage.
Zinc protects the liver against the oxidative damage caused by sporidesmin and for many people, is the preferred method of protection. The most practical way of supplementing sheep with zinc is to give Time capsules®. These are zinc boluses given orally that sit in the rumen and slowly release zinc over a period of 6 weeks. Zinc can also be administered as a zinc oxide slurry drenched weekly. This is effective but not practical for large numbers of sheep. It may be an option for lifestyle blocks. Cattle options for supplementation are zinc sulphate via the water supply either through a dosatron or Peta dispenser. Zinc oxide drenched, added to supplement, sprayed on pasture or in the form of Time capsules®, are also available.
Other options for managing your way through the facial eczema risk period include using fungicide sprays e.g. Mycotak. The key to effective control using this method is to spray before spore levels rise too high. If levels have crept much over 100,000 then you have probably missed the boat. Fungicide spraying will be effective up to 6 weeks from the time of application. Risk can also be minimised by attention to grazing practices - avoid known hot spots during the danger period e.g. north facing sheltered gullies, avoid pushing stock down into the base of the sward where levels are at their maximum, consider using conserved feeds, utilise fodder crops where practicable.
The risk is still very real at the moment and, despite our latest spore counting seeing a reduction in the average across the district to 18,000, some of our testing sites still remain up at around 80,000 and no doubt some untested sites higher again. If you have initiated some control measures already, then keep it up at this stage. If you haven't, then hopefully you are assessing the danger on your property as the season progresses.
At Totally Vets we have weekly spore counts on our website, an option to register for our weekly email facial eczema bulletin, and plenty of knowledgeable and willing vets to field any queries.
