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🐑 Sheep Ectoparasite Welfare

Blowfly Strike

Cause and Progression

Blowfly strike occurs when blowfly species (primarily Lucilia sericata in the UK) lay eggs on sheep, usually in areas soiled by faeces, urine, or fleece rot. Eggs hatch into larvae (maggots) that feed on the sheep's skin, rapidly causing tissue destruction. The smell of a struck sheep attracts more flies, accelerating progression.

Welfare impact is severe and rapidly progressive:

• Initial strike causes intense irritation and pain — struck sheep show characteristic stamping, nibbling at affected area, and hunching
• Untreated strike within hours causes deep tissue damage with necrosis
• Toxic shock can occur in severe cases
• Without treatment, strike is fatal within days

Prevention

• Prevention products: Pour-on and dipping insecticides (cypermethrin, dicyclanil, diazinon formulations) provide protection for 8–16 weeks during the high-risk period (May–September in the UK)
• Dagging: Removing soiled wool around the breech before the fly season dramatically reduces strike risk
• Shearing: Earlier shearing reduces fleece depth that traps moisture
• Controlling predisposing conditions: Treating diarrhoea, footrot, and fleece rot reduces strike risk
• Daily monitoring: During the fly season, all sheep should be checked at least once daily — even a 24-hour delay worsens outcomes significantly

Treatment

Struck sheep require immediate treatment:

1. Remove affected fleece and expose all maggots
2. Apply a licensed maggot-kill product (e.g., organophosphate dip, cypermethrin)
3. Administer pain relief (NSAIDs) — blowfly strike is painful; analgesia is a welfare requirement
4. Assess whether antibiotic treatment is needed for deep tissue damage
5. Assess fitness for continued treatment or euthanasia for severely affected animals

Sheep Scab (Psoroptic Mange)

Caused by the mite Psoroptes ovis, sheep scab causes intense, chronic irritation. Mites trigger a hypersensitivity response causing intense pruritus (itching), wool loss, exudate, and crusting. Welfare impact is significant — affected sheep rub and bite constantly, lose condition, and the condition spreads rapidly through a flock.

Recognition and Welfare Impact

• Intense scratching, rubbing on fences, and nibbling at fleece
• Yellow-white crusted lesions progressing across the body
• Wool loss and damaged fleece
• Weight loss and poor condition
• Highly contagious — entire flocks can be affected within weeks

Treatment and Control

• Injectable macrocyclic lactones (ivermectin, doramectin) or organophosphate dips are effective
• All sheep in a flock must be treated simultaneously
• Strict biosecurity (quarantine of new purchases, checking for scab) prevents introduction
• Movement restrictions and regulatory involvement in some cases

Lice

Biting lice (Bovicola ovis) cause irritation, wool damage, and biting behaviour. Less severe than scab but still a welfare problem. Treatment with appropriate ectoparasiticides; not confused with scab — lice are visible with close examination of parted fleece.

Ticks

Ixodes ricinus (sheep tick) transmits louping ill (encephalitis), tick-borne fever, and tick pyaemia. All are serious welfare and production diseases. Tick control through ectoparasiticides and vaccination against louping ill where appropriate.