With facial eczema incidents on the rise, Gippsland farmers have been urged to closely monitor spore counts and to seek professional advice on an appropriate prevention regime.
Facial eczema is a liver disease caused by a toxin produced by a fungus that can grow in litter in the base of the pasture under the correct climatic conditions.
Given the right seasonal conditions, the fungus multiplies and produces a toxin that is ingested by grazing animals.
The toxin causes liver damage, which may result in a dramatic fall in milk production, metabolic disturbances and photosensitization of exposed skin, with severe pain.
Animals that survive facial eczema often suffer permanent liver damage and some never fully recover and require culling.
Zinc is protective against facial eczema. It prevents cell damage by forming an inactive complex with the toxin sporidesmin. It also inhibits intestinal absorption of copper, which catalyses formation of the oxygen free radicals that cause the cell damage.
In most cases, the first sign of facial eczema observed in a herd is some cows affected by photosensitisation. However, by this time, a large proportion of the herd is likely to have already suffered liver damage, for which there is no specific treatment.
Zinc supplements can be effective for facial eczema control and prevention if well managed.
Whichever option is used for zinc administration (zinc sulphate via drinking water, or zinc oxide administered by oral drench or included in the supplement fed in the dairy), the aim is to maintain the cow's blood serum zinc level at 20 to 35 micromoles/litre.
The desired dietary intake of elemental zinc required when prevention dosing to maintain this protective blood serum zinc level is 20 mg/kg liveweight/day. Zinc administration should commence 2-3 weeks before pastures become toxic. Feeding zinc oxide in grain/ concentrates (as a grain mix or pellet) in the bail at milking can be very effective for facial eczema prevention in the milking herd on Australian dairy farms.
However, the amount of zinc oxide included in each tonne of grain/ concentrate for "prevention dosing" must be carefully calculated to achieve the required dose of 20 mg elemental zinc/kg liveweight/day.
If under-dosed, cows will not be provided with adequate protection against high exposure to sporidesmin challenge. If over—dosed, there is the risk of zinc toxicity.
Problems supplying zinc oxide via grain/concentrate (as a grain mix or pellet) most often occur when:
*The incorrect zinc oxide inclusion rate per tonne of grain/ concentrate is used for the daily feeding rate and average milking herd liveweight.
*The zinc oxide settles out of the grain/concentrate before or during feeding
*Each cow does not receive and consume the intended amount of grain/concentrate (kg/cow/ day) in the dairy bail.
*The grain/concentrate feeding rate is changed mid-batch.
GippsDairy projects and events co-ordinator Karen Romano said it was critical that farmers have the right dosage and the correct timing when using zinc as a facial eczema prophylactic.
"We would certainly urge farmers to talk to their vet or their feed supplier if they unsure on how to deal with facial eczema related zinc supplements," she said.
Gippsland farmers can keep track of local pasture spore counts via the Dairy Australia facial eczema pasture spore monitoring program at www.dairyaustralia.com.au/.
