The warmer weather recently has been a lovely reminder that summer is on its way. As always, a new season brings a new set of diseases to be thinking about. When it comes to sheep and summer one important one to be aware of is Blowfly strike or in more vetty terms cutaneous myiasis. Blowfly strike has important welfare and economic implications for sheep flocks and is widespread across the UK with over 75% of farms reporting at least one case a year. Emily Moule from our Lancs vet team gives us a fresh reminder in her first newsletter piece of many!

Blowfly strike is caused by flies, in particular greenbottle flies (Lucilia Sericata) laying eggs in decomposing matters. Commonly affected areas include dirty back ends, open wounds and foot rot lesions. These eggs develop into larvae and then into maggots, a process which in optimum conditions can take as little as 3 days. These maggots feed on the skin and faecal matter and secrete enzymes leading to further skin and muscle damage. The damaged tissue releases toxins which, along with ammonia secreted by maggots, is absorbed into the bloodstream which can lead to systemic illness and may lead to death. Infected areas are also highly susceptible to secondary bacterial infections.

Clinical signs include:

Early cases: Irritation, nibbling at tail head, increase swishing of tails, rubbing and increased discomfort in lame animals

Severe cases: fleece loss, separation from flock, sick animals, death

Diagnosis is by clinical signs and appearance. Treatment involves clipping fleece around area, applying a maggot killing insecticide (see table below), and may involve pain relief and antibiotics depending on severity of case, do give us a call to discuss the best treatment options.
As with most things prevention is better than treatment and will reduce economic impacts as well as a clear reduction in the welfare implications for the flock. Measures include:

  • Fly treatment of flock at beginning of season (see table for recommended products or give us a call at the practice to discuss)
  • Regular inspection of flock to catch early signs
  • Reduce dirty back ends – dagging, and shearing at an appropriate time
  • Control worm burdens – give us a call to discuss the best options for parasite control for your flock
  • Treat lame sheep promptly to reduce footrot lesions attracting flies
  • Manage fly population – consider grazing more exposed pastures during high risk season, and remove carcasses promptly.

NADIS have a really useful Blowfly alert based on Met Office weather data
so you can work out what the current risk level in your area is. We will also bring you update on our facebook page, so please find us on there for the latest!

NADIS Website

Chemical Product Name Prevention Treatment Withdrawal
Cypermethrin Crovect, Ectofly,
6-8 weeks Yes 8 days
Alpha-cypermethrin Dysect,
8-10 weeks Yes 49 days
Diazinon Oxmonds
Golden Fleece,
Paracide 62
Up to 6 weeks Yes 49 – 70 days (depending on product)
Deltamethrin Deltanil, Fly
and Lice Spot
on, Spotinor
None Yes 35 days
Dicyclanil CLiK, CLiK
Extra, CLiKZiN
8-19 weeks No 7-40 days (depending on product)
Cyromazine Vetrazin 10 weeks No 28 days