Flystrike
Flystrike!
Just the word is enough to conjure up dread to any Australian sheep farmer. And Summer is the worst season for it. To understand flystrike, we first need to understand more about the culprits that cause the damage. There are basically two types of flies in most states of Australia and an extra one in Western Australia.
The main species of blowfly that initiates about 90% of all strikes is the Australian sheep blowfly. It is a copper green colour with reddish eyes. The adult fly is approximately 10 millimetres (mm) long and produces a smooth skinned white maggot. The damaged tissue and body fluid that oozes from the flystrike wound caused by L. cuprina attracts other species of flies. The hairy maggot fly, Chrysomya rufifacies is the most important secondary fly. It does not initiate flystrike, but readily invades flystrike wounds started by L. cuprina. It is blue green in colour, 10mm long and produces the characteristic hairy maggots. Adult flies usually live for approximately two to three weeks. Eggs generally hatch into larvae in 12-24 hours and larvae grow from pin head size to 10-15mm in length within about three days. They then drop off the sheep — usually at night or in the early morning when ground temperatures are coolest — and burrow into the soil to commence pupation a day or two later. This means that a large proportion will subsequently emerge as blowflies from around sheep camps. Adult flies will normally not travel more than three kilometres from where they hatch during their life span. After hatching, the female fly needs a feed of protein for her reproductive organs to mature. She needs a further feed of protein before egg laying. Common sources of protein are carcases, manure and existing strikes.
Factors that Increase the Likelihood of Flystrike
* The presence of primary species (most commonly the Australian sheep blowfly).
* Temperatures must be right (between 15–38 degrees).
* Recent rain — enough to keep suitable sites on the sheep moist for about three days.
* There must be suitable sites (wrinkles, injury, urine, faeces) on the sheep to attract flies and sustain larvae.
* Wind speeds below 9 kilometres per hour (km/h) as this gives flies the best opportunity to disperse.
Preventing and Managing Flystrike
Drenching
We are reasonably lucky with our Babydoll sheep that they are generally wrinkle free, especially in the breech area and they are short woolled. The Elliottdales are a little more at risk, with their long wool, but the hair tends to stop flystrike. The main areas for concern with them is the belly, the testicles and the udder, where the wool is non-existent or shorter. For the most part they are kept in smaller flocks, so it is easier to monitor them for possible flystrike. The main issue we face is that of worms, as worms create scouring, and scouring often brings flystrike with it. Similarly, to Body Scoring a “Dag Score” has been determined and it has been shown at a Dag Score 4, sheep can be seven times as susceptible to flystrike as a Dag Score 1, so control the worms to keep the breeches as clear as possible to minimize risk.
Tail Length
Ensuring tails are docked to the correct length (3 or 4 palpable joints) will also help keep the breech clean as it reduces the possibility of cancer and prolapse, as well as giving the sheep something to use to flick the flies away, stopping them from landing.
Crutching & Shearing
Along with worm control, crutching and shearing are key tools in the management of flystrike as it can occur anywhere on the body, where moisture is present. So not only the breech but the rest of the body needs to be checked for flystrike as well. Even though Babydolls have short wool, they need to be watched in the warmer months for bodystrike. The Elliottdales, with their long wool also need to be watched. Keeping them shorn and crutched, when necessary, will assist with this. Also keep an eye on any wounds or infections, such as Mastitis, abscesses, and lamb marking, as these too, will attract flies.
Signs of Flystrike
* Discomfort and agitation, rubbing of fleece can signify wool rot and hence body strike.
* Twitching of the tail, kicking, nibbling at wool, rubbing of the rear end.
* Isolation from the flock.
* General lethargy and weakness.
* Any discoloured wool or damp patches on the wool need to be checked out.
Treatment
Treatment of flystrike needs to be swift and the necessary chemicals need to be kept on hand all the time. This includes a good pair of sharp hand shears. If struck sheep are left untreated or incorrectly treated then sheep can suffer significant stress, produce tender wool, become vulnerable for restrike by a secondary blowfly species or death may occur. During periods of high risk it is important to check susceptible stock regularly. Often by the time flystruck sheep are found, the maggots have completed their development.
These maggots must be killed to stop them from becoming the next generation of blowflies that cause strike.
General principles for treating flystruck sheep include:
• Removal of struck wool. Clipping the wool allows for the infected skin to dry out as well as exposing maggot trails. Remove as many of the maggots as possible.
• Clipping should extend 4-5cm into clean wool to ensure all maggot trails have been exposed.
• Clipped wool should be placed in a plastic bag, sealed and left to dry out in the sun, thus killing the maggots.
• Dressing should be thoroughly applied to the infected area using a registered chemical. This prevents the area from being restruck whilst healing.
Sheep can be sprayed, jetted, dipped or plunged and there are a number of chemicals on the market to use.
As we have only had one or two sheep with small patches of flystrike, our go-to treatment is clip wool back, remove maggots and administer a thorough spray of Extinosad, wetting the fleece to the skin, followed by a dusting of Flystrike Powder. These are available at your Farm or Produce Store.
