Changing climate patterns are likely to put ewes at higher risk of parasitic disease, which could have important implications for farmers. 

Blowfly strike is the infestation of sheep by the parasitic larvae of the common greenbottle blowfly, Lucilia sericata.  Research, conducted at the University of Bristol, provides evidence that early season treatment of sheep can help reduce the blowfly population and protect animals from this disease. The study conclusions have helped shape the advice that industry provides to farmers regarding the use of pesticides; advice that, if followed, could help farmers respond to a changing climate and some of the challenges that it brings.

Over 80 per cent of UK sheep flocks are affected by strike annually. The welfare of between 500,000 and 1 million animals is compromised each year as a result of these infestations. For farmers, this brings economic costs both in the loss of animals as well as in the treatment and control of the disease.

For over 20 years, Richard Wall, Professor of Zoology at Bristol, has been studying every aspect of the biology of the common greenbottle. Recently, his research has focused on how changing climate patterns may affect the blowfly season as well as the population ecology of the fly.  He and his students have used computer models to simulate how fly populations might respond under predicted climate change scenarios, and to predict how changes in husbandry and control strategies may affect the incidence of blowfly strike. Their simulations suggest that longer blowfly seasons are likely, with adult flies emerging earlier in spring and maggots returning to the soil to over-winter later in the autumn.

“With earlier spring emergence, unless treated, the animals are unprotected for longer before shearing at the beginning of the year and the earlier the emergence, the higher the incidence of early season strike” says Wall. 

Once ewes are sheared, they are less susceptible to the disease as the short fleece no longer provides the attractive moist environment sought out by the egg-laying female flies.

“This presents a practical problem for sheep farmers,” says Wall, “because most farmers don’t want to treat ewes with long-lasting insecticides at the start of the season as much of the product would be lost when the wool is removed and the treatment of early-season lambs may delay getting them to market.  Even so, our research has demonstrated that there is an important welfare and economic case to suggest that this early season treatment will become increasingly important in the future, given warmer spring weather.” 

Novartis Animal Health, one of the funders of this research, has developed a short acting blowfly protection product that has a relatively short withdrawal period, particularly suited for use in early- and end-of-season treatments.

Wall’s body of research on blowfly has been funded by diverse sources including the Department of Environment, Food and Rural Affairs (Defra), the Natural Environment Research Council (NERC), the Royal Society, industry partners including Novartis Animal Health, and studentship support from the Biotechnology and Biological Sciences Research Council (BBSRC).