DEMONSTRATION OF THE SUSTAINED ANTHELMINTIC ACTIVITY OF A CONTROLLED-RELEASE CAPSULE FORMULATION OF IVERMECTIN IN EWES UNDER FIELD CONDITIONS IN NEW-ZEALAND

Ten field trials were conducted in the North and South Islands of New Zealand to evaluate the anthelmintic efficacy of an intraruminal contr olled-release capsule formulation of ivermectin. A total of 810 Coopwo rth, Perendale, Romney or Coopworth ' Romney ewes, weighing on average 42-70 kg, were used. Ewes were either untreated or treated shortly be fore lambing in late winter-early spring (eight trials) or in late spr ing (two trials) with an ivermectin controlled-release capsule which d elivers ivermectin at 1.6 mg per day for 100 days (minimum dose rate 2 0 mu g/kg/day). Bodyweights, faecal nematode egg counts and dag scores were determined before treatment and at about 2 and/or 4, 6 or 8, 10 or 12, 14 and 16 weeks after treatment. Ewes treated with the ivermect in controlled-release capsule gained on average 1.1 kg more than untre ated sheep over the 16 weeks of the trials, but this difference was no t significant (p > 0.10). Before treatment, faecal strongylid egg coun ts were equivalent (p > 0.10), but at each time point thereafter, egg counts in ivermectin controlled-release capsule treated sheep were sig nificantly lower (p < 0.01; p < 0.05 at Week 2). Dag scores were not d ifferent at the start of the trial (p < 0.10), but at the end of the t rial ivermectin controlled-release capsule treated ewes had significan tly lower scores (p < 0.01)than untreated ewes. These findings indicat ed that treated animals shed significantly fewer nematode eggs and the refore pasture contamination with nematode eggs should be significantl y reduced for at least 112 days. The control of dags should result in reduced direct losses due to the decreased value of dag wool, and indi rect losses due to the cost of dagging sheep and the cost associated w ith the treatment and control of flystrike initiated by dags in the br eech area.