This section desribes the processes for implementing a breeding and selection program that reduces the susceptibility of sheep to flystrike.
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Breeding and selection
Overview of breeding for flystrike resistance.
Breeding to reduce flystrike susceptibility
Four steps to breeding for flystrike resistance.
Visual Sheep Scores
Description, extract and link to the Visual Sheep Scores resource.
Australian Sheep Breeding Values
Description of which ASBVs can be used to breed for flystrike resistance.
Fleece Rot scoring and selection
How to score fleece rot.
Breech Wrinkle scoring and selection
How to score breech wrinkle.
Dag scoring and selection
How to score dag.
Breech Cover scoring and selection
How to score breech cover.
Question and answer
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Yes. It is possible to select and breed your flock for increased flystrike resistance by focussing on the traits that increase the risk of breech strike (breech wrinkle and dag, and to a lesser extent breech cover and urine stain) and body strike (fleece rot).
Despite the slightly unfavourable relationship between fleece weight and wrinkle it is possible to maintain or improve productivity and breed plainer sheep at the same time. The industry’s experience in breeding for reduced fibre diameter, whilst increasing fleece weight is evidence that this is possible.
1. Select rams with low wrinkle (and low dag, where dag is common) ASBVs.
2. Assess ewes for fleece rot, wrinkle, dag, urine stain and breech cover
3. Develop a joining strategy: breed the best to the best.
4. Assess your lambs and make a decision about mulesing and hogget classing
Preferably your ram breeder can provide ASBVs for wrinkle.
a) If no ASBVs are available for wrinkle—ask the ram breeder to provide breech or body wrinkle scores for the rams you are inspecting.
b) If no wrinkle scores are available, and breech wrinkle has been removed by mulesing—make a preliminary assessment for wrinkle using neck wrinkle and body wrinkle.
c) Consider changing to another ram source if your current ram breeder cannot supply rams that meet your needs.
Visual scoring provides an assessment of the susceptibility of the flock for both breech and body strike.
With this information you can;
The strategy should be to select against the worst X% of sheep in the flock, based on their fleece rot score. The value of X will depend on how much emphasis you want to put on this trait relative to other traits.
Sheep can be scored for fleece rot from 9 months of age. Scoring can be done at classing or shearing, provided there is a minimum of 6 months (or 40 mm) of wool growth to assess.
The best time to assess dag score in a winter rainfall region is in the spring time prior to hogget shearing when at least 20% of the flock have an average score of 2 to 3 (click to go to diagram). Consider culling all score 5 sheep prior to mating. Mark score 4 and score 3 ewes and note the number in the flock so that an assessment of how many of these could be culled from the breeding flock can be made.
Yes, In the summer dominant rainfall environment few sheep get severe dags, but those that do so in the fly season are at extreme risk. Therefore, it can be worthwhile to cull these sheep (same as culling sheep that actually get flystruck).
Generally, in environments where dag is sporadic or few sheep are affected, dag is better handled through management, rather than applying valuable selection pressure to dags, which could be used for other traits.
The importance of a bare breech in breech strike was investigated and it was found that it was less important than dags, urine stain and skin wrinkles. However it does play an important part as it can exacerbate the effect of wrinkles and dags.
Links to the other FlyBoss online learning topics