EFFICACY OF DORAMECTIN AGAINST WARBLE FLY LARVAE (HYPODERMA-BOVIS)

The efficacy of doramectin in the treatment of cattle harbouring natur ally acquired infestations of first, second and third instar larvae of Hypoderma bovis was determined in two studies carried out in the Burg undy region of France. In the first study, cattle on six farms with a history of H. bovis infestations were treated during October 1989 with either doramectin at a dose of 200 mug kg-1 liveweight (186 animals) or with an equivalent volume of saline (157 animals). During the follo wing March and April, all animals were examined for the presence of wa rbles. In the second study, cattle on four farms with warbles present in their backs were treated during March 1990, with either doramectin or saline (as before). The viability of larvae within each warble on a ll the animals was then assessed every 2 days for 14 days. In Study 1, no warbles were present in any of the doramectin-treated cattle at an y time, whereas warbles were found in 135 saline-treated animals. In S tudy 2, all larvae in warbles on the backs of the doramectin-treated c attle were dead by Day 14 after treatment, whereas viable larvae were still present in warbles in the backs of all saline-treated cattle. No adverse reaction to doramectin treatment was observed in any animal a t any time. It was concluded that doramectin is both safe and 100% eff icacious in the treatment of first, second and third instar H. bovis i nfections of cattle.