Farmers could lose over £200 for every lamb killed by flystrike
11th May 2023
An updated costing model has revealed farmers could lose £209 per lamb and £184 per breeding ewe that falls victim to blowfly strike, which means administering treatment only after animals are struck is no longer cost-effective.
Originally developed by the University of Bristol in 2019, the model has been updated in accordance with recent changes in farm economics, new information on insecticidal products, and the impact of a changing climate.
The estimated loss of £209 per lamb is based on the income lost from not selling the animal and the average cost of rearing a replacement lamb, while the loss of £184 per breeding ewe is based on the cost of rearing a replacement ewe lamb and the value of a cull ewe.
The update on the costing model was commissioned by Matt Colston, ruminant technical consultant at Elanco Animal Health, who said the figures highlight the financial consequences of blowfly strike and the importance of administering preventative treatment.
“The model looks at different management strategies – ranging from no treatment at all, to a combination of different treatments with preventative Insect Growth Regulator (IGR) products and pyrethroid products – in low, medium and high-risk scenarios for strike,” he explained.
“In all cases, preventative treatment for ewes and lambs is the most cost-effective strategy, and not treating sheep to prevent strike is likely to be the costliest strategy.”
In a medium-risk scenario, the model, which is based on a lowland 250-ewe breeding flock rearing an average of 1.5 lambs per ewe, predicts that 22 ewes and 36 lambs will be struck by blowfly strike. Assuming a 5% mortality rate, this comes at an estimated cost of £1,834 to the farmer, increasing to £3,483 in a high-strike risk scenario.
While the previous model suggested no treatment was a cost-effective option for low-risk flocks, this is no longer the case in the present circumstances, Mr Colston said. “This is due to an increase in the incidence of flystrike, alongside the higher market value of lambs in comparison to the cost of treatment,” he added.
To prevent avoidable losses, he encouraged farmers to assess their flock’s blowfly risk using Elanco’s Blowfly Forecast and to develop a control plan for the season ahead.
“A lot of farmers don’t realise that if they don’t put their preventative treatment on early in the season, more flies will have reproduced, resulting in higher populations by middle of the summer,” Mr Colston warned.
“By that point, the challenge can be very overwhelming and as this updated costing model shows, the financial consequences can be severe.”
For more information on blowfly strike and to access Elanco’s Blowfly Forecast, visit: www.farmanimalhealth.co.uk/sheep/sheep-blowflies
