Understanding how facial eczema occurs in cattle will help you better manage the disease.
Facial eczema occurs when cattle ingest spores of the fungus Pithomyces chartarum. The spores contain a toxin, called sporidesmin, which damages the liver and bile ducts. One of the first signs of facial eczema may be a sudden drop in milk production and a short period of diarrhoea.
However, often the most recognisable sign of facial eczema is inflammation of unpigmented skin and sensitivity to sunlight. This is called photosensitisation and occurs because the damaged liver is unable to breakdown products from the chlorophyll in grass, which builds up in the bloodstream.
Not all animals affected with facial eczema will show symptoms when liver damage has occurred. Research conducted in New Zealand suggests that for every one clinical case of facial eczema, there may be a further 10 cows with liver damage and reduced milk production.
Treatment and Prevention
The treatment for facial eczema is non-specific and is aimed at reducing pain and irritation associated with photosensitisation. There is no cure for facial eczema.
The fungus Pithomyces chartarum grows in the dead leaf material at the base of pastures in warm, moist conditions in late summer and early autumn. Monitoring pasture spore counts can assist with identifying periods of pasture toxicity and when to implement preventative strategies.
Feeding zinc is protective for facial eczema. To be effective, the cow's blood serum zinc levels need to be maintained in the range of 20-35µmol/L. This is most reliably achieved by feeding zinc oxide in pre-formulated pellets at the correct dose rate. Importantly, feeding zinc will not reverse existing liver damage.
Zinc supplementation of milking cows
Feeding the correct amount zinc oxide in grain/concentrates in the bail at milking can be very effective for facial eczema prevention.
If cows are underdosed (e.g. incorrect rate, settling out of the supplement, competition between cows) there may be inadequate protection from facial eczema.
Blood testing of cows in 12 herds during the 2019 season indicated that protective levels of zinc in the blood was most reliable when zinc oxide is fed in pelleted form. More inconsistent results were achieved when zinc was fed via a mineral dispenser or in a powdered form.
Serum (blood) zinc testing
It is recommended that farmers consider blood testing 10 cows in their herd 30-40 days after supplementation starts to check zinc levels are at the required level and adjust their program if required.
Experience in New Zealand indicates that accurate zinc supplementation at preventative levels is likely to be safe for up to 100 days. After this point, farmers should have blood testing repeated to minimise the risk of toxicity.
Zinc oxide boluses for dry stock
Other classes of livestock (e.g. bulls, heifers, calves, dry stock) are also at risk of facial eczema.
Controlled release, intra-ruminal zinc boluses commonly used in New Zealand are now available in Australia under an emergency use permit (PER 90370).
Farmers wishing to purchase boluses should contact their veterinary clinic. Veterinarians wishing to source boluses should email Nadine Krippner at Fortis Vets Ltd.
If treatment with zinc oxide boluses, or zinc oxide supplementation is not possible, access to high spore count pastures may need to be restricted. Consider:
Not allowing these animals to graze pasture to a short length, even if it means leaving long residuals
Supplementing stock with hay or silage to reduce pasture intake
In more extreme situations, twice weekly drenching with zinc oxide is an option.
With discontinuation of the Dairy Australia spore monitoring program in 2021, farmers are strongly encouraged to monitor their own spore counts fortnightly between December and May.
When pasture spore counts are trending upwards to 20,000 spores/gram and weather conditions look favourable for spore formulation, each farm should begin monitoring their pasture spore counts week to week or implement facial eczema prevention strategies.
Instructions for sampling pasture for facial eczema spore counting can be downloaded below. Pasture spore testing services are currently offered by the following veterinary practices:
West Gippsland Veterinary Centre (Warragul)
Gippsland Veterinary Group (Leongatha)
Yarram Veterinary Centre
Maffra Veterinary Centre
Bega and Cobargo Veterinary Clinic
Snowy River Veterinary Clinic (Orbost).
Veterinarians and advisors can learn more about facial eczema by reading A Review of Facial Eczema (Pithomycotoxicosis) - Report of the Dairy Australia Facial Eczema Working Group (updated 2013).
More details about zinc supplementation for facial eczema prevention are outlined in Preventing facial eczema in milking cows using zinc oxide in feed.
Protocol for Sampling Pasture for Facial Eczema Spore CountingPDF, 71.37 KB
A Review of Facial Eczema PithomycotoxicosisPDF, 2.22 MB
Preventing Facial Eczema in Milking Cows Using Zinc Oxide in FeedPDF, 231.41 KB