Most farmers associate Facial Eczema with peeling skin but this is just the tip of the iceberg as far as production losses are concerned. The main damage cause by sporidesmin, a mycotoxin produced by the fungus Pithomyces chartarum, occurs in the bile ducts of the liver. Extensive liver damage has been occurring for at least 2 weeks by the time signs of photosensitivity occur, and only about a tenth of the cows with liver damage will show any signs of photosensitivity. Facial Eczema can cost our dairy industry as much as $100 million in a high challenge year.
Effective prevention of Facial Eczema involves monitoring the risk level, using spore counts and historical knowledge, and protecting the cows BEFORE they have significant exposure to sporidesmin. Pasture management to minimise the build-up of litter and avoid low residuals, use of fungicide sprays and feeding supplements to reduce pasture intake can all help reduce intake of spores. However, on most farms cows will still be ingesting some spores so zinc supplementation is needed to reduce the harmful effects of sporidesmin in the liver.
It is recommended to start at a preventative dose rate of zinc 2-3 weeks before spore counts are expected to rise, as this is far more effective than crisis dosing after the spore count has risen. It is also important to ensure all livestock receive the correct amount of zinc on a daily basis. Under-dosing with zinc allows more sporidesmin to cause damage and over-dosing can cause a sudden drop in milk, weight loss, rough coats, lack of appetite and sometimes death. Accurate knowledge of the liveweight of stock is important in calculating the correct dose rate, and power drenching or inclusion in feed generally give a more consistent daily intake than water treatment. Using a zinc product with ACVM registration and following label instructions will help ensure stock are well protected.
Recommended feed rates
2.1g elemental zinc per 100kg liveweight (9.5g for a 450kg cow) for longer term dosing.
32g elemental zinc per 100kg liveweight (14.4g for a 450kg cow) for crisis dosing