Facial eczema is caused by a toxin, sporidesmin, which cows eat when grazing pastures high in fungal spores. Trials conducted at AgResearch by Dr Neale Towers calculated the effect of low doses of sporidesmin on milk yield. Over a three week period, production across the herd had dropped by as much as 25%. For a cow producing 1.5kgMS, a 25% reduction in milk is $2.25 per cow per day lost (assuming a payout of $6.00/kgMS).
These cows did not exhibit any detectable liver damage when blood tested for GGT (an enzyme that indicates damage to the liver) which shows how significant the sub-clinical effects of facial eczema can be on production parameters. For every clinical case you see (e.g. redness of the udder, skin peeling, elevated GGT), there will be approximately 10-15 sub-clinical cows showing no signs or symptoms. There is also a lag between the ingestion of spores and the appearance of clinical signs, so monitoring and prevention strategies need to begin well before clinical signs appear.
Prevention is significantly less expensive than the losses from facial eczema. To reduce the number of spores ingested, dilution with other crops or feeds and spraying pasture with fungicide can all help reduce the number of spores consumed. However, in most cases feeding zinc that is registered for facial eczema prevention is also required to bind to the sporidesmin toxin to stop its chemical reactions from causing damage to the bile ducts. To be effective, it is important to get the zinc dose rate right. Blood testing your cows for serum zinc is the best way to determine whether enough zinc has been consumed to prevent the harmful effects of facial eczema. For cows, serum zinc needs to be between 20 and 35 μmol/L. It is best to sample from a range of liveweights to ensure small cows aren’t being over-dosed and large cows aren’t being under-dosed.
Nutritech have recently reformulated their facial eczema range to provide high quality zinc and mineral supplementation options to suit different on-farm application methods. AquaMin® Zinc is designed for administration via the water, FloZinc® via drenching systems and Nutrimin® Zinc via feed. AquaMin®Zinc, FloZinc® and NutriMin® Zinc all provide an ACVM registered zinc for facial eczema prevention, plus organic copper and trace elements. NutriMin® Silage Balancer Zinc also includes calcium, sodium and magnesium to provide a more complete mineral balancer during the facial eczema season. The use of organic copper in these Nutritech facial eczema products helps ensure cattle do not become depleted in copper while high rates of zinc are being fed.
When should zinc supplementation stop? Facial eczema can continue long into April and May – just because the autumn flush has come doesn’t mean that the facial eczema risk is low. As long as the pasture spore counts are >30,000 spores/g, the risk to your livestock is too high to stop zinc supplementation. It is best to continue to get your pastures tested to know when it is safe to stop.
This article was originally published in The Farmlander December 2020