Breeding for flystrike resistance to be made easier

Breeding for flystrike resistance to be made easier


Genetic research into the heritability of flystrike susceptibility in sheep is set to be incorporated into new tools to assist breeders to make more informed selection decisions.


Genetic research into the heritability of flystrike susceptibility in sheep is set to be incorporated into new tools to assist breeders to make more informed selection decisions. 

Tracie Bird-Gardiner, from the NSW Department of Primary Industries, has spent the last four years collecting and analysing data from fly-struck sheep in the industry’s Information Nucleus Flock (INF), under a postgraduate study scholarship provided by the Cooperative Research Centre for Sheep Industry Innovation (Sheep CRC).

Mrs Bird-Gardiner’s analysis has provided industry with a deeper understanding of the genetic heritability of flystrike resistance, including how to identify susceptible sheep using indirect markers, and how the trait responds to the environment and interacts with other genes that drive flock productivity.

Her findings are set to feature in an app under development by the Sheep CRC to assist producers to monitor the health and productivity of their flock, and predict when individual animals may be at risk from disease and weather events.

“My thesis focused mainly on breech strike data collected at the Trangie and Cowra INF sites, where conditions can result in longer periods of flystrike risk compared to the summer and winter dominant rainfall areas,” Mrs Bird-Gardiner said.  

“The research identified potential indicator traits for breech strike which could be used for indirect selection in breeding breech strike-resistant sheep in a non-seasonal rainfall environment.”

She said yearling breech wrinkle was identified as a key indicator trait for breech strike.  

“Although selection for reduced breech strike and breech wrinkle was found to have a small unfavourable correlation with fleece weight, this can be taken into consideration when making selection decision,” Mrs Bird-Gardiner said. 

“The repeatability of susceptibility to breech strike was also evaluated and it was found that there is a fairly high likelihood that ewes struck at their first lambing are likely to be struck again in following years. It is therefore important for producers to carefully consider whether they want to keep these sheep in their breeding flock.”

Mrs Bird-Gardiner received her Masters degree at a graduation ceremony last week at the University of New England, Armidale. She chose flystrike as her research topic due to its importance for the sheep industry and its significance as an animal welfare issue.

“I’ve always been interested in animal breeding and, working on the land, I have had to treat countless sheep for flystrike.  I couldn’t see what was stopping us from coming up with a better solution, such as breeding flystrike resistant sheep,” she said.

Mrs Bird-Gardiner said the inclusion of flystrike resistance into future genetic selection indexes would assist breeders to balance any negative correlations with other traits. 

In the absence of an index, she recommended producers undertake their primary selections based on the production traits they are seeking to improve in their breeding objective, then conduct a secondary selection based on flystrike susceptibility indicators.

“The key indicator traits identified for risk of breech strike in the non-seasonal rainfall zones were yearling breech wrinkle, crutch cover, neck wrinkle and wool cover and breech cover estimated at marking age. Interestingly, there were differences in the ranking order of key indicator traits for other environments, confirming that breech strike indicator traits vary with the environmental conditions,” she said.  

The data gathered by Ms Bird-Gardiner will support new prediction models being developed by the Sheep CRC for inclusion in its app to assist producers to identify risks before flystrike occurs.


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