Breeding and Selection of Sheep to Lower Flystrike Risk

The goal for all sheep producers is to reduce the impact of flystrike on flock welfare and productivity.

For producers who have decided to phase out mulesing, the goal is to breed a flock that has low susceptibility to breech strike and can be managed effectively without the need for mulesing.

Breech wrinkle and body wrinkle traits are closely related and highly heritable (as heritable as body weight, staple strength, and staple length). Also, dag, breech cover and wool colour are moderately heritable. This means that there are substantial opportunities for producers to breed more flystrike resistant sheep and phase out the practice of mulesing.

The fastest way to breed a flock with low susceptibility to breech flystrike will depend on your region.

Where scouring resulting in dag is NOT common
(typically Queensland, northern NSW and lower rainfall areas)

• Select rams with favourable Australian Sheep Breeding Values (ASBVs) for wrinkle or low visual wrinkle scores.
• Score ewes for wrinkle and segment them based on flystrike risk. Apply culling and joining strategies that will rapidly reduce the proportion of high wrinkle score sheep in the flock.
• Apply other management procedures that will reduce the risk of flystrike, particularly in the early stages of a breeding program if susceptibility to breech flystrike is high.

Where scouring resulting in dag is common
(typically the southern half of Australia, excluding low rainfall areas)

• Follow the 3 points above AND include selection for dag.
  Some of these areas, such as WA and SA, are more likely to already have plainer (less wrinkled sheep) and dag is the major risk factor for flystrike.

Body strike can also be reduced using similar strategies to those discussed above for breech strike. Fleece rot is the primary selection trait to breed for reduced susceptibility to body strike. Fleece rot is moderately heritable therefore like breech strike there is a great deal of opportunity to reduce body strike using breeding strategies. At this stage there are no ASBVs for fleece rot although they are expected to be available in the near future. The expression of fleece rot is significantly affected by seasonal conditions therefore ASBVs will be a great benefit for across- year and across-flock selection. Until ASBVs are available to select rams and when selecting flock ewes, select relative to the average expression in the group of sheep rather than to a particular score. Highly resistant flocks may have the luxury of only selecting Score 1 (no fleece rot) sheep.