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Tips on Blowfly Strike in sheep

Fly strike (myiasis) can affect all sheep and is caused primarily by the blowfly Lucillia sericata. Once the initial strike has occurred, however, other species can escalate the problem by laying their eggs onto the site of the primary strike – this is called secondary strike. Blowfly ‘strike’ lives up to its name. In warm humid weather, significant damage can occur in as little as 36 hours. The areas most prone to strike are the withers, flanks and the tail area, particularly after scouring. Open wounds are a real attraction for flies and hence vulnerable to strike. The economic losses of fly strike can be devastating with damage affecting wool clip, leather quality and live weight gain – increasing time to market. The welfare implications are particularly serious as the effect on animals is severe. If left untreated, fly strike can quickly prove fatal.

There are two main types of product that can be used to control blowfly strike. Insecticides such as organophosphate (OP) dips and synthetic pyrethroid (SP) pour-ons are one option. Insect growth regulators (IgRs) offer a popular solution with a long duration of protection. A recent survey revealed more farmers in the UK choose IgRs than any other type of blowfly prevention.2 IgRs such as dicyclanil are available in formulation as CLiK® which offers an unrivalled 16 week protection, or as the new formulation CLiKZiN®, which offers eight weeks cover but with only a seven-day meat withhold. CLiKZiN has been launched this year and can be used where medium term protection with a short meat withhold period is required. With the meat withhold on Vetrazin® recently increased to 28 days, CLiKZiN® should give your customers the flexibility to still market lambs as needed and with the confidence that their flock is protected

Should blowfly strike occur, treatment must be prompt to minimise the discomfort caused and to prevent productivity losses, even the death of affected animals. In cases of strike, an SP pour-on, such as cypermethrin (Crovect®) can be used for treatment. Having suffered strike, it is also important to advise farmers on the need to implement on-going strike protection and the value of long-term treatment.

IgRs – BREAKING THE BLOWFLY CYCLE The efficacy of IgRs in preventing blowfly strike is based on their unique ability to break the fly lifecycle. This effectively stops the ‘fly waves’ from developing. There are three larval stages between egg and adult known as L1, L2 and L3. IgRs prevent the development of harmless L1 stages (that have no biting mouthparts) into the harmful L2 and L3 stages. It is the L2 and L3 larvae that burrow into the sheep’s skin and cause production losses and welfare problems.

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