Blowfly alert relaunched as farmers count cost of losses
© Michael Nolte/Wirestock Creators/Adobe Stock A service that alerts sheep farmers to the risk of blowfly in their locality has been relaunched by the National Disease Information Service and Elanco.
Blowfly Watch – which is now a free service – uses modelling predictions and meteorological data mapping to help farmers, vets and advisers target treatment and monitoring of flocks.
See also: Emerging livestock diseases – another unwanted climate change effect
The relaunch follows a 2023 study that put the cost of mortality caused by blowfly strike at £209 a lamb and £184 a breeding ewe.
These costs would be even higher this year, given lamb prices, according to Elanco’s technical ruminant consultant, Matthew Colston.
“Blowfly strike is common, and most flocks are at risk. Strike happens fast – within 24-36 hours of eggs being laid – causing severe damage,” he says.
In addition, changing seasonal patterns mean the blowfly season is starting earlier and lasting longer.
Cost-effective strategy
Matthew says the strike study, by Katie Lihou, Fiona Lovatt and Richard Wall (published in In Practice), concluded that early preventative treatment is always the most cost-effective strategy for blowfly (see “Prevention”).
“That’s key, because a lot of farmers will wait until they see the first sheep struck on their farm before they take action. Our aim is that no sheep should suffer the trauma and pain of fly strike.”
Early warning
Subscribers to Blowfly Watch receive early warning fact sheets advising them how to assess risk on farm, depending on factors such as type of system and sheep breed, and how to prepare for blowfly treatment. These factsheets are followed by real-time blowfly alerts.
Information is mapped in 40km squares throughout the UK and used to predict when the blowfly is starting to hatch.
Alerts are categorised as follows:
- Green squares indicate flystrike is unlikely as temperatures have not reached levels where hatching is expected
- Amber squares mean hatching is now likely. Farmers in these areas are alerted to be vigilant and use preventative treatment
- Red squares show flystrike is very likely.
For the past year, a network of 100 flocks across the UK has been reporting first cases of flystrike. This information has been used to improve the model, says National Disease Information Service veterinary adviser Phillipa Page.
However, Matthew points out that the service is a guide and there will be local and farm-specific environments that mean hatching can occur before, or after, predicted timings.
Prevention
Preventing blowfly strike starts with minimising risk factors, says Elanco’s Matthew Colston.
In the short term, this means addressing any lameness and wounds, as well as ensuring there is no faecal soiling of fleece. It is also important to be aware of high-risk areas on the farm: these tend to be sheltered areas with a lot of tree cover where temperature and humidity are generally higher than elsewhere on the farm.
“Longer term, we can look at flock genetics. Wool-shedding sheep are much less likely to be struck than heavily fleeced sheep. Individual animals differ in their ability to attract flies, so we can breed animals that are less susceptible to flystrike,” says Matthew.
“We can also look at tail length: long-tailed sheep are much more likely to be struck than short-tailed sheep.”
The next stage is to try to manage the fly population on farm. This involves taking the following actions:
- Check the risk forecast
- Start early to interrupt fly lifecycles so blowfly populations are far lower going into autumn, reducing strike risk
- Minimise blowfly breeding opportunities by removing dead stock
- Apply preventative treatments before any animals get struck.
Treatment options
- Insect growth regulators give eight to 19 weeks’ cover, depending on the product
- Synthetic pyrethroid pour-ons give eight to 12 weeks’ cover, depending on the product
- Organophosphorus plunge dips give six weeks’ cover
Source: Sustainable Control of Parasites
How to sign up for Blowfly Watch
The service is free via Elanco and is still available as a paid subscription service from Nadis
Blowfly basics
- The greenbottle, Lucilia sericata, is the most common blowfly associated with strike in the UK
- It lays its eggs on animals with soiled or damaged skin (as well as dead animals)
- Eggs hatch and once the larvae have developed into maggots, they burrow into skin and eat the underlying flesh