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Record rainfall across Eastern Australia throughout spring and summer 2010-11 resulted in a boom season for graziers, but the lingering warm, wet conditions also proved the perfect environment for flystrike. But not all flocks were as affected with a group of Merino producers proving that it is possible to breed sheep that can survive in hot, humid conditions without regular chemical treatment, or mulesing.
Why Does Flystrike Occur?
Merino sheep in Australia have traditionally been bred to have skin wrinkles on the body and breech regions. When the skin of the breech region is constantly wetted by urine, it becomes scalded and is prone to breech strike. Mulesing has been used as a management tool over the years to help prevent breech strike but has no impact on body strike incidence. Sheep that require mulesing have skin wrinkle over the body and when wet by persistent rain, fleece rot develops and body strike can occur.
Finding a Genetic Solution
As well as increasing the quality and quantity of wool produced, the SRS® Breeding System also reduces the animal’s susceptibility to flystrike. In order to have a Merino sheep that is naturally resistant to all types of fly strike (body, breech, pizzle, poll etc), the animal needs to have a radically different body and fleece appearance (Figure 1) to the Merino types generally found in Australia. The sheep are plain bodied with minimal wrinkle (Figure 2), are open-faced and often bare breeched. The fleece is thin stapled with highly aligned wool fibres that grow much longer than is seen in most Merino flocks.
Some of SRS® Merino producers are now shearing their sheep at about 80 to 90 millimetres fleece length every 6 months, or twice a year, and many, three times every two years. This is the required combing length, being neither too short nor too long. The sheep are producing 4 to 5 kilograms of 17 to 20 micron wool at each shearing.
The fleece of an SRS® Merino is always white with a low suint content (Figure 3) and the wax is unable to be emulsified by suint (non-saponifiable). These factors make sheep difficult to wet to skin level and the wool dries quickly.
Case Studies from the Coal Face
Pat and Sue Hegarty’s commercial Merino property, “Colanya”, recorded 425 millimetres of rain from the end of September 2010 to the end of February 2011. Despite the constant damp conditions less than one per cent of the 7200 non-mulesed Merino sheep were affected by flies.
The recent wet summer was the ultimate test for the Hegarty’s breeding program which began 10 years ago to breed plain-bodied, fertile and heavy cutting sheep requiring little effort to manage. “We put a cull mark on everything that was fly struck, because as the percentage was very low (0.8%), we may as well be rid of them. Of 66 rams in the ram paddock only one was struck on the breech. We have had a few horned ones blown on the heads a few weeks back that we cleaned up and are OK,” Hegarty says.
“Ten years ago before we started selecting for the type of sheep we do now I would probably expect to have had as much as 30 per cent of the flock flystruck in a summer like this.
“We haven’t mulesed here since 2006. The sheep are shorn in May and treated off-shears for lice and then crutched in December or January. Apart from that we don’t treat them at all,” Hegarty says.
SRS® Poll Merino studbreeder Errol Brumpton has been breeding sheep for flystrike resistance, amongst other traits, since the early 1970’s. He witnessed stranded sheep dying in their droves from flystrike in the 1974 floods and since then has given fly strike resistance high priority in his comprehensive SRS® breeding program at Well Gully, near Mitchell in South West Queensland. The climate where Errol and his wife Candy operate their 2400 hectare grazing operation swings between extremes – a hot, humid summer where temperatures can reach 48 degrees Celsius and a cold frosty winter. Well Gully receives an average 525 millimetres a year, with most of this falling between September and March.
“I’ve found that if there is anything wrong with the skin structure of the sheep in this climate they will definitely get body struck in the summer months. Blowfly strike has pushed a lot of sheep out of this district because people found they were spending a lot of their time jetting sheep. We do not mules our sheep and we don’t jet and we do not get any breech strike or body strike other than a few isolated cases,” says Brumpton. The Well Gully sheep are treated only once with chemicals - at lamb marking time with a spot of chemical on their backsides after their tails have been removed “A lot of our clients, particularly further north are one man shows. When it rains in the Channel Country they can be cut off from their sheep for a long time. They need sheep that are easy to manage and will survive if the shearers can’t get into the property for a few weeks because it is too wet.”
“I learned from a very young age that free growing, long stapled sheep rarely get flyblown. If the wool is well aligned and has a white wax it will absorb very little water and will dry out rapidly.”
“We had an incredibly wet humid summer this year with 800 millimetres of rain from November to January, and 290 millimetres in March. I couldn’t believe what I saw. There was no body strike at all and one case of breech strike among the 4200 ewe and lambs. There was virtually no fleece rot and the wool was still pure white,” he says.
Wellington, New South Wales
Bruce and Carol Taylor, “Boxleigh Park”, Wellington also have had little problem with body strike. On their commercial Merino operation of 5,000 Merino ewes further west at Carinda, their son Geoff Taylor, who manages the property, says “I don’t think we had one case of body strike all year, despite 725 millimetres of rain. The conditions were pretty much perfect for fly strike, being so wet. I checked the sheep regularly but we did not have a problem which was a relief.”
Contact Us: For more information on the SRS® Breeding System or sourcing SRS® genetics please contact:
Dr Jim Watts
Chief Scientist and Breeding Consultant
The SRS Company Pty Ltd.
Tel: +61 2 48622050