EFFICACY OF IVERMECTIN IN A CONTROLLED-RELEASE CAPSULE FOR THE CONTROL OF BREECH STRIKE IN SHEEP

Objective To investigate the efficacy of ivermectin in an intraruminal controlled-release capsule (CRC) against blowfly strike. Design Pen a nd field trials with controls, Animals Pen studies: Two breech strike trials involving 60 Romney and 60 Merino sheep. One body strike trial using 100 Merino sheep. Field trials: Eight trials in New Zealand used 1000 Romney and Romney-cross sheep. Fifty Merino lambs in one trial i n Australia. Procedure Pen studies: Sheep were allocated to two equal groups. One was not treated, the other sheep received a CRC that deliv ered ivermectin at greater than or equal to 20 mu g/kg/day for 100 day s. In the breech strike trials, each animal was given an oral laxative 2 days before exposure to adult Lucilia cuprina. In the body-strike t rial, the sheep sheep were kept wet to increase susceptibility prior t o the release of blowflies. Field trials: Fifty or 200 sheep allocated to equal groups of nontreated or treated with the CRC and grazed at p asture exposed to natural blowfly challenge. Results Pen studies: Bree ch strikes developed in 24 of 60 controls but in none of 60 CRC-treate d sheep. There was a 35% reduction in the number of CRC-treated sheep struck on the body. Field trials: The average number of breech strikes in CRC-treated sheep was reduced by 86% (P < 0.001). The number of bo dy strikes in the treated groups was a reduced by 27% (P < 0.05). Conc lusion The ivermectin CRC is a useful aid in controlling breech strike , but provides only moderate reduction in the incidence of body strike .