Blowfly Strike in Sheep
Blowflies are one of the most widespread ectoparasite affecting sheep in the UK. Surveys suggest that every year 80% of flocks will have one or more cases of strike. The severity of strike can be hugely variable year by year and can be weather related but not treating promptly can lead to reduced performance, secondary infections and death. Leaving animals untreated when knowingly affect with strike is also a welfare issue.
In the UK, blowfly strike is usually caused by the greenbottle fly. The females are attracted by the odour of decomposing matter such as wounds, soiled fleece or dead animals. Each female lays up to 250 eggs which hatch after about 12 hours. After 3 days the mature larvae drop off the sheep and pupate in the soil. Blowfly strikes usually occur in waves. The first fly lays her eggs and the odour from this strike attracts other flies. When the populations of larvae become overcrowded they will attack the living tissue of the sheep. The first signs in affected sheep are a patch of discoloured wool and agitation. Rapid diagnosis and treatment are essential.
Traditionally, we expect to see blowfly strike between May and September but with changing weather patterns, lowland flocks are at risk from March through to December. With increasing flock sizes and the need to rationalise labour use to improve profitability, flocks must have a plan that will provide protection during the risk period and fit with the need to control other parasites.
Blowfly strike can be prevented through the application of an appropriate product before a period of challenge. The table overleaf contains a list of the products currently licensed for this use.
Products Licensed for Prevention and/or Treatment of Blowfly Strike 2016:
|Product||Company||Chemical Name||Blowfly Product||Lice Control?||Tick Control?||Withdrawal|
|CLiK||Elanco AH||Dicyclanil (IGR)||16 weeks Protection||None||None||40 days|
|CLiKZiN||Elanco AH||Dicyclanil (IGR)||8 weeks Protection||None||None||7 days|
|Crovect||Elanco AH||Cypermethrin||Treats and 6-8 weeks protection||Kills existing lice||Up to 10 Weeks||8 days|
|Ectofly 12.5mg/ml||Bimeda||Cypermethrin||Treats and 6-8 weeks protection||Kills existing lice||No||8 days|
|Deltanil||Virbac||Deltamethrin||Treatment only||4-6 week reduction in incidence||6 Weeks||35 days|
|Dysect||Zoetis||Alpha-cypermethrin||Treats and 8-10 weeks protection||Kills existing lice||8-12 Weeks||49 days|
|Fly & Lice Spot On||Zoetis||Deltamethrin||Treats only||4-6 week reduction in incidence||Up to 6 Weeks||35 days|
|Spotinor 10mg/ml||Norbrook||Deltamethrin||Treats only||4-6 week reduction in incidence||6 Weeks||35 days|
|Vectocert 1.25%||Downland||Cypermethrin||Treats and 6-8 weeks protection||Kills existing lice||Yes 8 weeks||8 days|
|Vetrazin||Elanco AH||Cyromazine (IGR)||10 weeks Protection only||None||No||28 days|
|Zermasect Sheep||Downland||Alpha-cypermethrin||Treats and 8-10 weeks protection||Kills existing lice||8-12 Weeks||49 days|
* IGR = insect growth regulator. These products do not stop the fly laying here eggs, but the larvae do not fully develop preventing the strike.
REMEMBER, when using these products ALWAYS read the manufacturers instructions on dose rate, storage and withdrawal periods. Check application equipment is working properly and is calibrated. Replenish dips according to instructions and follow safety guidelines.
Information correct at the time of publishing – check the data sheet and product packaging before applying the product and check the application rates and/or withdrawal durations have not changed.