Facial eczema, both clinical (symptomatic) and subclinical (non-symptomatic), is a major cause of production loss in dairy herds throughout New Zealand. Subclinical cases are thought to be 10x higher than clinical cases within the herd, which means many farmers don’t realise facial eczema is a problem until it’s too late.
Facial eczema is caused by a toxic fungus called pithomyces chartarum, which grows at the base of summer pastures. Triggered by humidity and high temperatures, this fungus grows rapidly and produces spores containing sporidesmin, a toxin that damages liver and bile ducts, and causes toxin build up in the body. This causes photosensitisation, with sunburn usually seen 10 days after spore exposure.
Getting it right
Zinc is essential for growth, reproduction, milk production, immunity, and hoof health, and supplementing with zinc is the most common and effective way of guarding against facial eczema, however there’s a lot potential for mistakes. A 2014 study of 1200 cows across 105 North Island dairy farms found that approximately 70% of cows weren’t getting enough zinc to provide protection. This can be due to underestimating liveweights, inaccurate dosing, and supplementing with low-quality products.
Timing is also crucial. For best protection results, zinc dosing should start two to three weeks before spore counts begin to rise, usually from December to January (however, with temperatures expected to rise earlier this year, farmers should be prepared to start zinc dosing accordingly). Every farm will have different spore counts and close monitoring of these will identify periods of toxicity in the pasture.
Maintaining protective levels
Zinc forms a stable complex with sporidesmin, disrupting the production of liver-damaging toxins and preventing damage to the liver. To be successful, supplements must send zinc directly to the liver. This is best achieved when zinc supplements are in sulphate or oxide forms, instead of chelated.
Zinc can be dosed in multiple ways: through the trough system, drenching, slow-release zinc boluses, via grains in-shed, or added to premixes on the feed pad. Whichever method you choose, the effective blood serum zinc level is 20-35 micromoles/litre. Zinc supplementation intake to maintain this level is 20mg/kg liveweight/day. Use only a quality zinc supplement and continue to take blood samples to ensure the blood serum zinc level is stable. Under-dosing will negate protection, but overdosing can cause toxicity.
By the time cows are showing the classic signs of facial eczema – skin reddening and/or peeling, drop in production, restlessness – a large proportion of your herd will likely be experiencing liver damage. There is no specific treatment for liver damage, so making a solid facial eczema prevention plan is the best defence against this devastating disease.
Article: Chris Balemi, Agvance Nutrition. First published in Dairy News, September 2023
Sources:
Dairy facial eczema an underrated issue
Dairy Australia drives herd and feed innovation
Preventing facial eczema in milking cows using zinc oxide in feed