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Breech Genetics


Horned Merino rams.

Reducing the risk of flystrike, particularly breech strike, in the Australian sheep flock is a key investment area for AWI in ultimately working to reduce reliance on mulesing.

Breeding naturally resistant sheep is the long term, sustainable solution to reducing the risk of breech strike. However, an integrated approach to reducing the risk of breech strike will always be required involving a combination (dependent on regional risk factors and sheep type) of;

  • timely annual shearing and crutching
  • accelerated shearing or crutching
  • worm control, drenching and paddocking
  • fly control including chemical treatments
  • short timely lambing periods
  • proactive marketing of wool and surplus livestock sales, as well as
  • breeding for low wrinkle, low dags, low urine stain and low breech wool cover.

 AWI supports genetic research and development to identify sheep with high natural resistance to flystrike.

Since 2007, research has been underway at two key sites (Armidale NSW and Mt Barker WA) to identify sheep with high natural resistance to breech strike.

These trials indicate that a range of factors affect sheep differently in different environments. 

Sheep most at risk of breech strike:

  • 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

Australian Sheep Breeding Values (ASBVs) for the key traits related to flystrike (Breech Wrinkle, Breech Cover and Dag) are now available for many sires.

Recent trial results indicate there are good prospects for reducing the incidence of flystrike over the longer term by breeding for key flystrike resistant traits, i.e. reducing breech wrinkle, breech wool cover, dags and urine stain.

However, the three-and-a-half year Merino breeding cycle (average generation interval) and the need to maintain sheep productivity, health and welfare both slow the rate of progress towards a naturally flystrike resistant flock. Unfortunately, breeding for lower wrinkle generally leads to decreased fleece weights, but sheep that are relatively high in fleece weight and low in wrinkle have been identified and Industry is selecting and breeding from these to ensure they maintain and or increase productivity whilst decreasing wrinkle in their flocks.

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 were released in late 2009.

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.

Education and extension programs are readily available to woolgrowers wanting to more efficiently select and breed naturally flystrike resistant profitable sheep to reduce the reliance on mulesing for managing the risk of breech strike.

The length and severity of the blowfly season is highly dependent on environmental and climatic factors (rainfall, temperature, humidity, wind speed, altitude, worm type and burden etc). These highly variable environmental factors affect the incidence of breech and body flystrike and it means that there is no single solution to fit all sheep breeding programs.
Breeding strategies customised to individual woolgrowers environmental challenges and sheep type will increase the rate of progress toward natural flystrike resistance in sheep.

Further Information

"Latest Publications" on Breeding

Genetic research trial results - click the links below to read or download newsletters with the latest results from genetic research trials:

Breeding for breech strike resistance -  click the following links to download presentations on research into breeding for breech strike resistance: