Huge rainfall, mixed with high humidity and warm temperatures at night, have dairy farmers from across Victoria on alert for facial eczema in their cattle.
Facial eczema, or photosensitivity, occurs when cattle ingest large amounts of fungal toxins that can be found on perennial ryegrass pasture and is associated with skin irritation.
Non-pigmented areas of skin and mucous membranes become reddened and thickened, in particular, udders, teats and eyes.
"Highest risk pastures are those with lots of dead leaf litter and the most toxic part of plant is that closest to the ground," Dairy Australia's national animal health and fertility lead Zoe Vogels said.
"The skin can become crusty and peel away.
"Cows may be restless, seek shade and lick or rub affected areas."
The skin signals were secondary and could be seen two weeks after the primary liver damage, where toxins produced by fungal spores concentrated in a cow's bile ducts and generation of free radicals damaged the liver.
Local pasture spore counts co-ordinated by GippsDairy and Dairy NSW show sites at Tinamba, Vic, record 60,000 eczema spores per gram in the week ending January 28, while their Yannathan, Vic, site has recorded 35,000 eczema spores per gram.
Dairy Australia advises that farmers implement preventative measures for eczema when spore counts trend towards 20,000 eczema spores per gram.
Dr Vogels said spore counts could vary between dairying areas, farms within an area and even between paddocks on the same farm.
"While facial eczema is most prevalent in Gippsland and southern NSW, instances of the disease have occurred in other areas of Victoria and South Australia," she said.
"The occurrence of facial eczema depends on the cows eating high levels of the fungal spores on perennial ryegrass pasture and so, in theory, facial eczema could occur wherever there are ideal conditions for spore growth.
"Pastures tend to become toxic in late summer and autumn."
Stuart Crosthwaite, Hermitage Dairy, Kergunyah South, Vic, said the issue wasn't something too widespread on his farm, but he always monitored for it.
"We do see it from time to time here, but I don't think we have to deal with it too frequently," he said.
"There is one heifer that we had on our farm that currently has it, but we just keep an eye on it."
Mr Crosthwaite said the linkages that the disease had to the liver meant that he generally was able to pick it up in his cattle.
"We had a vet initially work with us, but we have had experience for 20 years here, and we are able to diagnose it fairly well now without their help," he said.
Dr Vogels said dairy farmers who lived outside of prevalent areas where facial eczema existed should "make themselves aware of how the disease presents and investigate any occurrences with their veterinarian".
Farmers should also look to control strategies through pasture and grazing management by moving cows to safer pasture areas or avoid grazing below four centimetres of pasture.
Feed supplementation could also help.
Dr Vogels said feeding zinc oxide was a preventative.
Ideally cows should start being supplemented with it two to three weeks before pastures become toxic.
"Zinc prevents cell damage by binding with the toxin (but does not reverse liver damage already done from exposure to the toxin)," she said.
"Zinc oxide can be administered to dairy cows in feed during milking or given as a slow-release bolus in dry stock.
"If animals are underdosed (for example, incorrect dose rate, settling out of the supplement, competition between cows) there may be inadequate protection from facial eczema.
"Overdosing has also resulted in cases of zinc toxicity."
She said it was important that the amount of zinc included in the grain or concentrate was accurately calculated to ensure cows received the correct dose rate.
"Farmers can blood test a sample of cows in their herd 30 to 40 days after supplementation starts to check zinc levels are within the required range and adjust their program if required," she said.
"For farmers using long-acting zinc boluses, animals should be weighed prior to administration and the correct bolus size used."
