Pauline Inwood: High spore count poses FE risk

Facial eczema is preventable in sheep and cattle. Photo / File

Now that there has been some rainfall, we must continue to be vigilant in preventing facial eczema (FE).

Even as little as 5ml of rain followed by humid and mild conditions with night temperatures above 12C will allow the spores to multiply.

It is a fallacy to assume that spore numbers will only be high if mushrooms are present in pastures. On highly-fertile pastures, mushrooms may not thrive, but FE spores will. Spore counts around the Bay of Plenty and South Waikato have been extremely high (hundreds of thousands to millions of spores/gram) in the last few weeks. From that high base, even without substantial rainfall, spores are present and can start another exponential growth phase when we do get decent rainfall.

Most dairy farmers treat their stock by medicating their drinking water with zinc sulphate or drenching stock daily with zinc oxide. But in the presence of overwhelming numbers of spores, this may not be sufficient to prevent liver damage. A two-pronged approach of treating animals and spraying pastures may be needed. There are sprays available from stock and station agents which can be used to kill the fungus on pasture, but the pasture must be sprayed at least every 4-6 weeks. This assumes absolute and complete coverage which renders the pasture safer after a short period.

Treating the water supply may be less effective because some animals drink less than others and the dose may be diluted in the trough as the day wears on. The stock must have no access to any other water source.

There are now zinc capsules available for sheep and cattle which release zinc for 4-6 weeks, but it is important to know the weights of the animals. Although these capsules look huge, if correctly administered the animals are able to swallow them safely. You can however, drench animals with zinc oxide once every 3 to every 7 days. The capsules are not licensed for alpaca or deer, which may also be susceptible to FE.

* What is facial eczema?

Facial eczema occurs when grazing animals consume large numbers of spores over a short period or smaller numbers over a longer time of the fungus Pithomyces chartarum which is present in the base of all pasture. When the right amount of moisture and warmth allow it to multiply, the fungus produces thousands of spores which are ejected into the pasture. In heavy rainfall, these spores are washed off leaves and into the base of the sward, where they develop into more fungi so the cycle is accelerated.

All species can become affected when grazing these spores as they are digested and produce a toxin called sporidesmin which is excreted through the liver to the bile ducts, inflaming and blocking the ducts and causing a build-up of bile. Excess bile and the digested remains of chlorophyll, phylloerythrin in the bloodstream cause the symptoms we see. Where blood vessels pass close to the skin in unpigmented (white or hairless areas) the phylloerythrin in the blood reacts with sunlight to cause intense irritation so animals will scratch these areas or seek shade. But the more serious damage is being done to the liver and can only be seen by a blood sample.

* How can we prevent FE?

The other treatment is to give the animals zinc either through drinking water, by drench or capsule. Treatment of the water supply must start before the numbers of spores is too high and it is better to treat with capsules before there is a massive challenge. Your vet will be able to advise you about treatment and also on the risk of rising spores in your area.

Many sheep breed societies and some cattle breeds are tested for FE resistance. This means they are able to tolerate increased numbers of spores. Lifestylers should select rams which have a history of FE testing, if possible, since sheep are more susceptible than other livestock, probably because they graze lower in the pasture sward than other species except horses.

* What to do for affected animals?

Providing shade and good feed is essential when animals are affected. A drench with Manderson's Mix can help provide some relief, but it is not a cure. Give them a zinc capsule and vitamin B12 as well. Older animals, with previous liver damage will die of this disease, so don't prolong their misery. If they go down and can't or won't get up they should be humanely destroyed. Badly affected animals aren't suitable for human consumption because of jaundice.

For more information, or help with dosing animals please call me or email me for a fact sheet.

Pauline Inwood, BVSc BAgSc (Hons) MACVSc, can be contacted at paulineinwood@hotmail.com