Managing Facial Eczema (FE) requires a multipronged approach involving strategies to reduce spore intake and provide zinc as a prophylaxis and therapy.

FE is caused by a mycotoxin produced by the fungus pithomyces chartarum growing in pasture dead matter. This fungus multiplies rapidly when overnight temperatures are above 13 degrees Celsius and when there is moisture available. The fungal spores are ingested by livestock and release a toxin called sporidesmin, which is concentrated in the bile of the liver causing significant liver damage. This causes phylloerythrin, a breakdown product of chlorophyll which builds up in the blood stream and reacts with sunlight causing photosensitivity and the lesions we recognise as FE. By the time you see the physical signs of FE, there is already significant liver damage in a large proportion of the mob.

Pasture spore counting is used to estimate the FE risk of a paddock. Paddocks sprayed with Prolific (containing carbendazim) when spore counts are low but rising, can significantly reduce the proliferative growth of the fungus for a period of up to six weeks. Summer forage crops (turnips and rape), herbs (plantain and chicory), clovers, Italians all have lower FE risk.

Zinc also helps to reduce FE incidence. The mycotoxin in sporidesmin is a thiol compound. Thiols react with certain metals to form stable compounds called mercaptides that do not cause tissue damage. Zinc is a mercaptide forming metal and is able to prevent and limit tissue damage from the sporidesmin. It is important to note that chelated zinc does not have this protective effect.

Copper has the opposite effect to zinc by catalysing the auto-oxidation creating more liver damage. The best strategy is to elevate copper levels in stock before the FE risk period, and if supplementation is required then use a chelated copper product.

Zinc prevention needs to occur two to three weeks prior to the risk period to build up to protective levels in the animal (see Zinc dosing, on the right). When spore counts are rising towards 30,000 begin zinc supplementation so that by the time counts actually reach 30,000, the animals are receiving 2 g of zinc per 100 kg. The zinc content of supplements varies, so check with your PGG Wrightson store or Technical Field Representative to calculate the correct dose for the product that you are using. Blood samples can be analysed to check that the animals are receiving a protective dose.

Zinc can be supplied in two forms, through supplementation in water or products such as The Time Capsule®. The Time Capsule is a safe and easy to use bolus that leaves no residue and removes the guess work from dosing. The Time Capsule contains zinc oxide providing four weeks protection in cattle and six weeks in sheep in handy weight ranges. Repeated treatment extends this protection period.

If animals are affected with clinical FE, it is still worthwhile treating them with zinc. Treatment helps to reduce the continuing liver damage and allow for recovery. If you are going to supply the zinc through water or feed, then give animals an oral drench to lift levels quickly and safely.

Zinc dosing: Steps for when to start treatment

Step 1: Monitor regional spore counts

When regional counts trend upwards to reach 20,000, continue to Step 2.

Step 2: Monitor farm specific counts

Choose four paddocks that are representative of the farm. When farm specific counts rise to reach 30,000 continue to Step 3.

Step 3: Weigh a selection of cattle

Accurate live weight measurement is essential to ensure the correct bolus size or mixing rate is being used. Guesswork leads to error!

Step 4: Dose cattle with full zinc rates

If spore counts are over 30,000, cattle should be dosed with a full dose of zinc: 2 g of elemental zinc per 100 kg liveweight per day.

Step 5: Is my programme working?

Have you ever checked your dosing method is effective? Recent New Zealand trial work has highlighted that approximately 70 percent of zinc dosing programmes don’t achieve protective levels. Measure serum zinc and GGT three to six weeks into your programme.

For advice around FE treatment or prevention, contact your local PGG Wrightson Technical Field Representative or store.

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