Facial eczema is a disease associated with the fungus Pithomyces chartarum, which grows on dead grass at the bottom of short pasture.
In hot, humid weather it produces spores containing the mycotoxin 'sporidesmin'. This is toxic to the liver and bile ducts in cattle and sheep. When the liver and bile ducts are damaged, phytoporphyrin (a waste product from breaking down the chlorophyl in plants that are consumed), cannot be excreted and builds up. High levels of phytoporphyrin cause hypersensitivity to sunlight and lead to severe sunburn.
It's peeling skin from sunburn that is the most obvious sign of clinical facial eczema, but this tends to happen about 10-14 days after the toxic dose of sporidesmin and the resulting liver damage.
A high dose of zinc in the rumen of your stock is the main way to help prevent facial eczema, along with monitoring spore counts across your farm and and only grazing lower-risk pasture or crops.
Spraying pasture with fungicide can be worthwhile, but spore count monitoring still needs to be done to ensure it's effective, and to tell when it runs out! Rain can also affect application success. Re-application over time or due to weather is usually necessary.
There are a few different ways of giving stock zinc, from in-water or in-feed, to daily oral drench or longer acting boluses.
Zinc sulfate in water works well for adult dairy cows. However, it does not taste very nice, so it's recommended to introduce it slowly over about five days so cows can adjust to the taste. Make sure there is no other untreated water available, or else cows will simply avoid drinking the treated water. Cows need to be getting 25-30g/cow per day when dosed this way, and even then it's not very effective when there's a high challenge of spores.
Zinc oxide can be given in feed, but when dosing this way intakes of zinc may end up different between cows depending on if they eat more or less of their share of meal. The zinc needs to be well mixed into the feed to ensure all cows get some, so mix your feed and zince in a mixer wagon or choose a pelletised feed option.
Zinc in an oral drench can be a good way of ensuring every individual cow gets an appropriate and effective dose every day.
Zinc in a bolus is an ideal option for youngstock and drystock, as it ensures a steady dose of zinc for six weeks, when another 4-week top-up can then be given. We stock Face-Guard zinc boluses in our farm store in-clinic and recommend them if you're going to use boluses. These are designed differently from Time Capsule boluses, which can sometimes dissolve at a faster rate than required, giving a higher daily dose and not lasting as long as expected.
Your zinc dosing system and it's effectiveness against facial eczema can be monitored by blood testing 10 cows 3-6 weeks after your zinc supplementation has started. We test for both zinc levels and liver damage with GGT levels. This is a great way to check your method of supplementing is working.
Every farm and stock situation is different, so if you'd like help to navigate your options for supplementing and monitoring, get in touch with your KeyVet or pop in and see the team.
Plus, don't forget you can also get some grass samples tested to see what spore levels are like on your farm.
