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Breech Genetics


Horned Merino rams.

Breeding naturally resistant sheep is the long term, sustainable solution to managing the risk of flystrike in Australian wool sheep. AWI supports genetic research to identify sheep with high natural resistance to flystrike.

Trials at several sites across Australia indicate that different factors, in different environments have differing affects on the level of flystrike resistance in sheep.

Sheep most at risk of flystrike have higher degrees of skin wrinkle and/or wool cover in the breech region and/or are more susceptible to dag accumulation and urine staining of wool.

Recent trial results indicate there are good prospects for reducing the incidence of flystrike over the longer term.

However, the three to three-and-a-half year Merino breeding cycle (average generation interval) and the need to maintain sheep productivity, health and welfare slows the rate of progress towards a naturally flystrike resistant flock.

Tools for Breeding Flystrike Resistant Sheep

AWI's genetic research into natural flystrike resistance and Sire Evaluation led to the development of three new tools for sheep breeders. Australian Sheep Breeding Values for Breech Wrinkle, Breech Cover and Dag

Sheep breeders can use breech trait scoring charts like the one below to select sheep with higher natural resistance to flystrike. The scores provide a consistent language for scoring sheep traits across the country.


Breech cover standard from Visual Sheep Scores pocket guide.

Sheep and stud breeders can use standardised Sheep Breeding Values (across-flock genetic benchmarks) for breech wrinkle traits to identify sires with enhanced natural resistance to flystrike.

These Sheep Breeding Values are derived from a very large number of individual sheep records in the Australian National Merino Genetic Database.

Increased availability and use of these breeding tools will accelerate the rate of wool industry progress toward naturally flystrike resistant sheep. The use of these tools is already occurring in the breeding strategies of stud breeding operations and commercial woolgrowers across Australia.

Education and extension programs are readily available to woolgrowers wanting to more efficiently select and breed naturally flystrike resistant sheep, and to manage the risk of flystrike without mulesing sheep.

The varied environmental effects on the incidence of breech and body flystrike means that there is no one-size-fits-all sheep breeding program.

Only breeding strategies customised to the environmental challenges and genetic mechanisms on each individual farm will increase the rate of progress toward natural flystrike resistance in sheep.