Sheep death and loss of production associated with flystrike in mature Merino and crossbred ewes

Abstract

In eight well-managed Australian Merino and crossbred sheep flocks the adult ewes were monitored frequently for flystrike. Occurrences of flystrike and severity of strike scores were recorded, whereas bodyweights and condition scores were recorded regularly across two wool production and reproduction cycles. In these unmulesed flocks, 17% of Merino and 5% of crossbred ewes were struck, with 2% of those struck dead within 7 days of detection of the strike. For those adult ewes that survived the immediate period of the strike, the rate of loss over the following year was slightly greater than for ewes that were never struck, particularly for those with a high severity strike. Flystrike also contributed to losses of up to 2.7 (Merino ewes) and 5.2 (crossbred ewes) kg of bodyweight, and 0.3 condition score units at the time of the strike. Bodyweights were still 2 kg lower by 3 months after the strike occurred for Merinos, although condition scores returned to average levels. For ewes struck between mating and lambing, flystrike was associated with significant losses of lambs. Flystrike at severity level 1 (light) had only minor effects on wool production, but severity score 3 (heavy) reduced clean fleece weight.