Mortalities due to blowfly strike could be costing farmers £209/lamb and £184/breeding ewe, according to an updated blowfly costing model.

The updated model now reflects the most recent changes in farm economics, new information of insecticidal products and the impact of a changing climate.

Developed by the University of Bristol, the model shows that the estimated loss of £209/lamb is based on the income lost from not selling the animal and the average cost of rearing a replacement lamb.

The loss of £184/breeding ewe is based on the cost of rearing a replacement ewe lamb and the value of a cull ewe.

Ruminant technical consultant at Elanco Animal Health, Matt Colston, said the new figures highlight the financial consequences of blowfly strike and why preventative treatment is paramount.

Colston said 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.

“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,” he said.

Financial implications

The model is based on a lowland 250-ewe breeding flock rearing an average of 1.5 lambs/ewe and predicts that 22 ewes and 36 lambs will be struck by flystrike in a medium-risk scenario.

The financial implications of this, based on a five percent mortality rate, are an estimated cost to the farmer of £1,834, and this increases to £3,483 in a high-strike risk scenario.

Colston highlighted that, although the previous model suggested that no treatment was a cost-effective option for low-risk flocks, this is no longer the case.

“Relying on the identification of struck animals and then administering treatment is no longer cost-effective,” he 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.

“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.

“By that point, the challenge can be very overwhelming and as this updated costing model shows, the financial consequences can be severe.”