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.


METHODS
Pen and field trials with controls.


METHODS
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 in Australia.


METHODS
Pen studies: Sheep were allocated to two equal groups. One was not treated, the other sheep received a CRC that delivered ivermectin at > or = 20 micrograms/kg/day for 100 days. In the breech strike trials, each animal was given an oral laxative 2 days before exposure to adult Lucilia cuprina. In the body-strike trial, the sheep sheep were kept wet to increase susceptibility prior to the release of blowflies. Field trials: Fifty or 200 sheep allocated to equal groups of nontreated or treated with the CRC and grazed at pasture exposed to natural blowfly challenge.


RESULTS
Pen studies: Breech strikes developed in 24 of 60 controls but in none of 60 CRC-treated 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 body strikes in the treated groups was a reduced by 27% (P < 0.05).


CONCLUSIONS
The ivermectin CRC is a useful aid in controlling breech strike, but provides only moderate reduction in the incidence of body strike.
Rugg
D
D
Merck Research Laboratories, Somerville, NJ 08876, USA.
Thompson
D
D
Gogolewski
R P
RP
Allerton
G R
GR
Barrick
R A
RA
Eagleson
J S
JS
D000818:Animals; D002214:Capsules; D003692:Delayed-Action Preparations; D005243:Feces / Q000737:chemistry; D005260:Female; D015994:Incidence; D007306:Insecticides / Q000008:administration & dosage / Q000032:analysis / Q000627:therapeutic use*; D007559:Ivermectin / Q000008:administration & dosage / Q000032:analysis / Q000627:therapeutic use*; D008297:Male; D009198:Myiasis / Q000453:epidemiology / Q000517:prevention & control / Q000662:veterinary*; D011897:Random Allocation; D012756:Sheep; D012757:Sheep Diseases / Q000453:epidemiology / Q000517:prevention & control*
D002214:Capsules; D003692:Delayed-Action Preparations; D007306:Insecticides; D007559:Ivermectin