Prepare now or risk strike, sheep farmers warned

A sheep farmer, based near Milton Keynes, has reported the first incidence of blowfly strike in the region, warning other farmers that the parasite season is already threatening flocks in the area.

Blowfly strike is one of the most unpleasant yet familiar annual problems that sheep farmers need to deal with. It is caused by the infestation of sheep by fly maggots which feed directly on the skin of affected animals, causing serious distress and welfare problems and in some cases death. In the UK, blowfly strike occurs on over 80 per cent of sheep farms1. Experts have warned farmers that prevention is better than cure because once a strike has happened sheep can die very quickly.

Overwintered blowfly larvae will begin to develop in the soil as temperatures rise above 9oC, and can mature very quickly; when temperature’s reach this level, the start of the strike season will not be far behind.

Fiona Lovatt, President of the Sheep Veterinary Society explains: “Due to the unpredictability of the UK weather, getting the timing right for treatment of ewes and lambs against blowfly strike can be extremely difficult. Incidence of blowfly strike will rise with the local soil temperature on a farm, and some areas of a farm may be warmer than others. Flies will begin to emerge from overwintered blowfly pupae as the soil temperature rises above 9oC and larvae can mature in as little as 3 days after the eggs are deposited in the fleece of a susceptible sheep.

Dr Lovatt continues, “Many do not realise the speed in which blowfly strike can occur, as within days of emerging, adult females lay batches of about 200 eggs onto the sheep’s fleece. If an infestation is missed, then the sheep will suffer for a week or so before dying. Thankfully blowfly strike can easily be prevented but research has shown that there is a very good reason to use such treatments early in the year to prevent a build-up of flies and avoid the devastating impact that strike can have on flocks.”

There are three species of blowfly which can affect sheep in the UK, with the greenbottle (Lucilia sericata) being the most common. Blowfly larvae develop through three stages between egg and adult; it is within stages two and three that the larvae cause damage to sheep, known as blowfly strike, which can lead to production losses and welfare problems.

Fiona Anderson, vet advisor at Novartis Animal Health comments: “Prevention is always best in the case of blowfly strike because adult flies can lay so many eggs in the fleece and the strike can establish very quickly. Farmers have so many demands on their time it can be easy to miss an affected sheep. An infestation can be easily prevented through the use of products which contain insect growth regulators (IGRs) such as CLiK® and CLiKZiN®. These inhibit the development of the damaging second and third stage maggots which are responsible for causing fly strike and stock damage.”

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