Clinical Signs

Blowfly Strike is a serious disease thought to affect over 80% of farms in the UK.

‘Blow’ refers to the laying of eggs by flies and ‘Strike’ is the damaged caused by the larvae (maggots).

The Cause

In the UK, strike is caused primarily by the green bottle fly, Lucilia, which seeks decomposing matter to lay her eggs. Carcasses, dirty backends, foot rot lesions and open wounds are all good candidates for egg laying sites. 

Female Green Bottle Fly

Female flies lay batches of 200 eggs at each oviposition, so fly populations will quickly increase over a short period of time in the summer months.

Welfare/Economics

Blowfly strike has a serious impact on the welfare of sheep within the UK, as well as having a major impact on productivity. Figures from 2015 suggests blowfly strike costs the sheep industry £2.2 million per year.

Losses are incurred from:

  • Welfare
  • Loss in productivity (weight loss and decreased milk yield)
  • Fleece damage
  • Deaths
  • Treatment costs; including product, labour and time

Disrupted grazing occurs when sheep are affected by blowfly strike, this in turn leads to weight loss/decreased weight gain

Disrupted grazing occurs when sheep are affected by blowfly strike, this in turn leads to weight loss/decreased weight gain 

Flocks should be carefully checked at least once a day throughout the blowfly season to look for any signs of blowfly strike. It is often necessary to handle animals and part the fleece to fully appreciate the extent of disease.

Early Signs of Strike

  • Irritation
  • Nibbling at tail head
  • Increased swishing of tails
  • Rubbing
  • Further signs of discomfort in lame animals

Nibbling of tail head in this lamb affected by strike is affecting its grazing, which in turn will lead to decreased daily live weight gains.

Nibbling of tail head in this lamb affected by strike is affecting its grazing, which in turn will lead to decreased daily live weight gains.

Footrot lesions may also attract flies to lay their eggs. In these cases the lameness will be exacerbated.

Signs of Severe Strike

  • Discoloured/damp fleece
  • Fleece loss
  • Separation from flock
  • Sick animals
  • Death (due septicaemia from secondary bacterial infection and release of toxins)

Untreated strike has resulted in the death of this animal. The feeding maggots have damaged extensive areas of skin, this will attract more flies

Untreated strike has resulted in the death of this animal. The feeding maggots have damaged extensive areas of skin, this will attract more flies