FACIAL Eczema (FE) is primarily a severe disease of cattle, sheep and deer that is caused by the fungus Pithomyces chartarum that grows mainly on rye grass pastures.
The fungus produces spores that release a potent mycotoxin (sporodesmin) in the gastrointestinal tract after the ingestion of contaminated forages.
Sporodesmin causes severe damage to the liver, bladder and udder of affected livestock.
Although signs of photosensitisation affecting non–pigmented skin are a marker for the disease, only about one in 10 affected animals displays photosensitisation, however the rest of the mob will still be experiencing liver damage and may have significant production losses through weight loss or reduced weight gain, reduced milk production and occasionally death.
The highest risk period for FE is late summer and early autumn as warm and wet conditions are needed for the spores to germinate.
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The highest concentration of spores tends to be found in the base of pastures where there is more dead leaf litter.
The initial clinical signs of FE after exposure to high levels of sporodesmin is often a bout of diarrhoea and a sudden drop in milk production that may last for up to five days followed by recovery.
Subsequent exposure to high levels of spores results in more severe production losses with the typical signs of photosensitisation not occurring until about two weeks later.
Occasionally, bloody urine and cystitis (inflammation of the bladder) can occur in the weeks preceding a severe outbreak.
Young stock and dry cows are also at risk of FE with the early signs of weight loss or diarrhoea often being missed and FE not being recognised until the more advanced stages of the disease where significant photosensitisation is evident.
Obtaining a definitive diagnosis of FE is very important as there are many potential causes of a sudden milk drop, diarrhoea or photosensitisation with many different potential treatments and preventative measures.
A blood test to look for elevated liver enzymes is useful but only a couple of weeks post exposure to the spores.
A liver biopsy may be necessary to differentiate several different potential causes of liver damage.
There is no specific treatment for FE.
Providing shade to reduce the skin damage caused by photosensitisation is important.
Any areas that have skin that has peeled should be dressed with sun blocking ointments such as Zinc Cream.
Anti–histamines and anti–inflammatories may be helpful in reducing the pain and inflammation associated with photosensitisation in the early stages.
Cattle (but not so much sheep) can regenerate their liver after a bout of FE but it takes time and they may have ongoing issues the next lactation if liver damage is severe.
The best way to monitor the risk of FE is to conduct regular pasture spore counts.
Spore counts over 20,000 / g of pasture indicate a high risk of FE, however prolonged grazing of pastures with lower spore counts (eg 10,000 / g) can also pose a high risk as the effects of exposure to sporodesmin is cumulative. Spore counts can be performed by your local vet or pathology lab – submit at least 60 grams of pasture cut to one centimetre above the ground.
Prevention is based around avoiding exposure to potentially toxic pastures and may require dosing stock with very high levels of Zinc.
Zinc acts by binding with sporodesmin to prevent it causing cellular damage and also inhibiting the absorption of copper which is an important catalyst allowing the sporodesmin to damage cells.
Zinc takes a about two weeks to reach adequate blood levels to prevent FE.
A range of methods are available to dose cattle with Zinc that include water medication, daily or every second day drenching, feed medication and slow release boluses.
Water medication can only be safely done with specific dosing equipment and Zinc must not be added directly to a water trough.
Due to the wide variability of water intakes depending on weather and feed intake, water dosing is not recommended for high risk situations.
Whatever the method chosen, it is extremely important to blood test 10 to 12 cows about two to three weeks after starting Zinc dosing to check blood levels are adequate for control of FE.
Toxic and inadequate blood levels are common.
Although there is no information on how long it is safe to feed the very high levels of Zinc needed to prevent FE, the general recommendation is 100 days.
After which, careful monitoring of blood Zinc and Copper levels is recommended.
In summary, FE is a particularly severe disease that can have significant financial and animal health impacts.
Although photosensitisation is an easily recognised clinical sign of FE, it only occurs in about 10 per cent of affected animals.
The production losses in the animals not showing signs of photosensitisation is where the financial impact lies.
Regular monitoring of pasture spore counts is necessary to try and predict the onset of the risk period.
Extremely high doses of Zinc are effective at preventing FE but need to be started about two weeks before the risk of FE is high and careful monitoring of blood levels is needed to ensure the dose is effective but not toxic.
Given the unusual weather conditions being experienced across Southern Australia this summer, the risk of FE in 2023 could be very high and extend into areas that do not traditionally experience FE.
Contact your local vet for more information or check the Dairy Australia website for a thorough and in depth review of FE in Australia.
