Beware of blowfly strike

Crutching is highly effective as a preventative measure, says Roelof Bezuidenhout.

Beware of blowfly strike
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With the blowfly season approaching, attention is turning once more to blowfly strike, one of the most troublesome aspects of wool production. This costs farmers millions of rand every year in losses due to damage, and in time and money spent on control. One of the most effective ways for wool sheep farmers to reduce losses caused by blowfly larvae is to keep the rear ends of their ewes clean through ‘crutching’. This eliminates the moist spots where blowfly lay their eggs.

In crutching, any long wool on the area around the tail and down the inside of the legs is neatly removed with sheep shears.
The shorn area can then be treated with one of several types of anti-blowfly remedy. A pour-on product is useful as it can be administered easily and cleanly with a drench gun at 1cm3 per sheep. One treatment lasts for up to three weeks.

When applying chemical solutions, make sure to keep them out of any surrounding long wool. Chemical residues that contaminate the fleece will not be accepted by the wool industry. The nearer to the shearing date you are, the more careful you should be with the application of dips.

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New techniques
Not taking the trouble to crutch can lead to major losses. Blowfly strike affects the condition of the sheep, the quality of the wool and, if left too long, will kill the animal. Wool prices are currently so high that no farmer can afford to let even a kilogram go to waste.


Crutching a long-wool lamb.

 
Damage caused by blowfly larvae.

Clampdowns on chemical remedies may be on the cards, so now is a good time to investigate new ways of relieving the blowfly problem in an eco-friendly manner. Some sheep farmers are getting good results with a fly-trap system developed in Australia. The traps reduce seasonal blowfly population explosions without releasing harmful chemicals. And there is no way the flies can become resistant to them – a problem that is already occurring with many popular dips, pour-ons and injectables.

The trap is designed to catch the blowfly Lucilia cuprina, South Africa’s main attacking blowfly. This ‘primary’ blowfly is attracted to wool sheep as a good protein source for its larvae. Eggs hatch within eight hours and the larvae feed on the skin surface, attracting secondary blowflies to the victim.

Tails
It is possible to breed sheep with greater parasite resistance. Heavily pleated sheep and those with oily wool are more prone to blowfly strike, so select for plainer-bodied animals. And don’t cut the tails too short – a moving tail helps keep the pests away. Be particularly vigilant during hot, wet weather, when blowflies will tend to attack sheep almost anywhere on the body where the wool is moist. If you can, plan your shearing date to coincide with the period just before the main blowfly season.

Rams are prone to blowfly strike, too. Flies are attracted to open wounds around their horns caused by butting challengers. So check rams regularly and treat their heads with a recommended remedy. Rams and wethers with long wool can develop blowfly problems around their penises, so keep the wool in those parts short. Whenever you’re near the flock, check for any ewe or lamb that appears to be bothered by something – running, then stopping, or trying to bite at its tail. This type of behaviour is a sure sign of blowfly trouble.