Time to Strike Back on Flystrike!

Written By Bridget Parkman

No one likes chasing flies in the summer or at any time for that matter, so here’s a quick summary of some of the tools that could help to manage the fly risk on your property.

The FlyBoss Flystrike Risk Simulator gives us a quantifiable risk factor which guides us in putting management practices in place.

The contributing factors to an increase in susceptibility to flystrike in sheep, include wool quality traits such as fleece rot, fibre diameter, fibre diameter CV and wool colour. A higher fibre diameter allows water to move more easily through the staple to wet the skin increasing the risk of fleece rot. Additional factors such as, conformation faults in the shoulders and back, tight horns, and lameness in the legs and hooves will all contribute to flystrike risk as they don’t allow proper moisture drainage and airing and can contribute to secondary flystrike due to the presence of proteins from infections. Such contributing factors can all be controlled through good genetic selection and management.

AWI’s latest Flystrike workshops have highlighted three critical phenotypic breech characteristics that influence breech strike risk, in particular, these include:

1.       Breech wrinkle

2.      Breech Cover

3.      Dag

All three of these traits are highly heritable so incremental improvements can be made when including them, and the other contributing factors mentioned above, into your breeding plan, in both mulesed and un-mulesed flocks.

The ASBV for breech wrinkle is ‘EBWR’, the ASBV for breech cover is EBCOV and the ASBV for dag is LDAG. Rams with more negative values for these traits will contribute genetics for less breech wrinkle, barer breeches and less dag. It is important to note, however, that dag and worm burden are generally not correlated, hence a low dag score does not mean no worms.

Such traits can reduce the incidence of breech flystrike by limiting the ideal conditions that cause it. These include the surface area for moisture to accumulate (wrinkle), the wool around the breech where urine and dag can build up (breech cover) and the proteins which Lucillia curpina are attracted to (dag build up). All traits can also be measured visually, we recommend recording a breech wrinkle and cover score at lamb marking on lambs within 2 – 10 weeks of age (see Figure 2) and a dag score on any lambs over 4 months of age within 60 days post season break, or if 30-40% of the flock are scouring). As with most traits that we can select for, there are negative correlations that come with these so always make balanced decisions across all traits.

Figure 1. below shows the benefits of decreasing your flock average breech wrinkle score by just one score and its effects on breech flystrike risk in a non-mulesed flock. 

Source: AWI StrateFly

Figure 2. Flystrike risk of a non-mulesed breech wrinkle 3 score vs breech wrinkle 2 score

Breeding is just one tool in the toolbox when combatting fly risk. Including the normal management strategies such as visual scoring, shearing, crutching and chemical intervention can further prevent fly strike during high-risk periods as shown in Figure 3 below.

Figure 3. Flystrike risk with additional management tools used

Source AWI: StrateFly

Bridget Parkman
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