There are a range of factors determining a sheep’s susceptibility to body strike.
The main predisposing factors are fleece rot and lumpy wool (dermo), which attract the flies and provide a focus for maggots—food and a suitable environment.
Susceptibility to fleece rot is affected by age, conformation (particularly on the neck, shoulders and back that allows water in and delays drying), fleece structure and wool quality (in particular, wool colour). Whatever the combination of factors, the result is a range of fleece rot expression that defines the potential for body strike. Fleece rot scores will be expressed at different levels depending on the current seasonal conditions. In dry seasons and low rainfall environments, lower fleece rot scores are likely to be recorded, regardless of the presence of the risk factors. However there is still the risk of fleece rot and body strike in the event of warm and wet weather.
Young sheep are the most susceptible to fleece rot, so ideally, sheep should be scored before their first adult shearing.
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.
The best approach is to review the mob of sheep and decide on the emphasis you want to place on all the traits in your objective. Then based on this emphasis establish a “general cut off standard” for fleece rot.
To obtain the best overall balance the general cut off is used but fine-tuned at the margins. For example, sheep with a fleece rot score of 3, 4 and 5 might be culled along with any score 2 sheep that also had weak performance (but not weak enough to cull independently) for another trait (eg structure of feet). Similarly a fleece rot score 3 sheep with high performance for production traits in the objective may be retained.
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.
To score, open the fleece at a minimum of three sites along the backline and look for evidence of staining and bands of crusting. The highest score across the sites is recorded.
For further information on fleece rot scoring download the NSW DPI fleece rot scoring Primefact below.
The flock scoring chart is a page where you can record fleece rot and wrinkle scores for your sheep (you can also use the same chart to score other traits).
Detailed instructions are on the downloadable file.