The toolkit to fight flystrike in sheep is getting lighter, with growing resistance to favourite chemicals a warning that the coming warm weather will bring a new wave of farming challenges.
"Historically flystrike is severe for one or two years in every seven but because of the statewide drought conditions we have been through, there has been a lid on the situation," said DPI Elizabeth Macarthur Agricultural Institute parasitology researcher Narelle Sales.
Australian Wool Innovation and the DPI recently published one of the largest insecticide resistance studies ever undertaken.
The Australia-wide study tested all of the blowfly treatment and preventative chemical groups to determine the resistance profiles of 100 submitted strains.
In NSW, maggot samples from 55 properties showed resistance to both dicyclanil (Click) and cyromazine (Vetrazin). Just recently another 23 NSW properties have been added to the list. The state is the only one in the nation where 100pc of submissions tested to date are resistant to both widely used chemicals.
As a result, management begins with producers rotating chemicals.
"If you use a chemical group to control lice, use another as a strike and wound dressing, then take these off the list of available chemicals as you need to select another chemical group to prevent flystrike," Ms Sales said.
One alternative is the neonicotinoid Avenge + Fly, which works for 14 weeks in long wool and is the longest alternative to dicyclanil.
Another is ivermectin (Coopers Blowfly and Lice) and spinosad (Extinosad). Organophosphates are still available but only as wound dressing.
Synthetic pyrethroids like Alpha-Cypermethrin (Vanquish) paralyse the female fly's ovipositor so instead of depositing neat clumps of eggs they are scattered, desiccate and don't hatch.
"The main message is to look at the active ingredients and don't just rotate between brands," Ms Sales said.
Genetic selection can help considerably to reduce susceptibility to blow fly in the first place, with LAMBPLAN and MERINOSELECT researcher, and team leader Dr Dan Brown, University of New England suggesting breeders could look to select away from body wrinkle, fleece rot, fleece colour, urine stain, breech cover and dags.
Some traits are highly heritable, like skin wrinkle, and sires chosen on phenotype are successful in this way, however Australian Sheep Breeding Values provide greater accuracy of selection
"When it comes to wrinkle we have quite good accuracy and thus confidence," he said. "With the less heritable traits like reproduction for example, estimated breeding values are much more accurate than just relying on phenotype alone. For example it is very hard to look at a ram and see how reproductive his daughters will be."
Look at the active ingredients and don't just rotate between brands
Another trait that is complex and only moderately heritable - and thus reliant more on ASBV selection - is resistance to worms and more work on this trait is on-going. However many breeders have managed to make significant improvements in resistance to worms.
Recent research and development has added to the millions of data points already in the program with more pouring in with new work on utilising genomics. As a result tools like ASBVs are becoming increasingly commercially relevant.
"Of course these are genetic aspects and they require long term commitment," Dr Brown said. "Producers need to work well in advance and continue over the generations."
At the centre of genetic selection is the balance between resistance to flystrike and meat or wool production. Antagonous traits will fight each other: An animal leaning towards smooth rolling skin will deal better with blow flies but might produce a lighter fleece. Favourable traits work together. Sheep that are more muscled tend to have slightly more lambs and are more naturally resistant to fly strike.
"We work with big data, which is collected by ram breeders and research flocks," Dr Brown said. "Today we have better tools to deal with the large variation that exists for most traits."
Producers of ultra-fine wool Dan and Sarah Calvert, Kalgara on the Gara, via Armidale manage their flock to avoid flystrike by selecting for certain traits, and vaccinate for barbers pole worm, leaving their chemical tool kit intact.
"We have not mulesed sheep since 2007. We gave it away because we were losing market share. To deal with that we have selected sheep that have a wrinkle-free breech. We cull after the first shearing," Mr Calvert said, also keeping a couple extra inches on the lambs' tails - a tip borne out by old research.
Traits like colour and fleece rot have already been bred out in their flock in their quest to produce better wool.
When it comes to selecting fine wool Merino rams with Australian Sheep Breeding Values that define traits resistant to flystrike, the job isn't as simple as it seems.
"We would like to buy rams with ASBVs but it can be difficult to find fine wool studs that do this," Mr Calvert said.
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