Demonstration of the sustained anthelmintic activity of a controlled-release capsule formulation of ivermectin in ewes under field conditions in New Zealand

Abstract

Ten field trials were conducted in the North and South Islands of New Zealand to evaluate the anthelmintic efficacy of an intraruminal controlled-release capsule formulation of ivermectin. A total of 810 Coopworth, Perendale, Romney or Coopworth ' Romney ewes, weighing on average 42-70 kg, were used. Ewes were either untreated or treated shortly before lambing in late winter-early spring (eight trials) or in late spring (two trials) with an ivermectin controlled-release capsule which delivers ivermectin at 1.6 mg per day for 100 days (minimum dose rate 20microg/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 ivermectin controlled-release capsule gained on average 1.1kg more than untreated sheep over the 16 weeks of the trials, but this difference was not significant (p > 0.10). Before treatment, faecal strongylid egg counts were equivalent (p > 0.10), but at each time point thereafter, egg counts in ivermectin controlled-release capsule treated sheep were significantly lower (p < 0.01; p < 0.05 at Week 2). Dag scores were not different at the start of the trial (p > 0.10), but at the end of the trial ivermectin controlled-release capsule treated ewes had significantly lower scores (p < 0.01) than untreated ewes. These findings indicated that treated animals shed significantly fewer nematode eggs and therefore pasture contamination with nematode eggs should be significantly 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 indirect losses due to the cost of dagging sheep and the cost associated with the treatment and control of flystrike initiated by dags in the breech area.

A cost-benefit analysis of pre- and post-lambing anthelmintic treatments to twin-bearing ewes on commercial farms in the southern North Island of New Zealand

“…In Experiment 1, mean lamb survival did not differ between treated and untreated ewes, but lamb survival explained 70% of the variation between trials in weight of lamb weaned per ewe (Miller et al 2015) and so this is likely to be a major driver of the financial returns on treatment in this study. As previous studies on commercial farms (Gogolewski et al 1997;Cook 2009) did not measure lamb survival or even weight of lamb weaned per ewe, it is likely that they missed important variables contributing to the cost-benefit of anthelmintic use. It is unclear from the current study why lamb survival would vary so much between trials, and in some cases between treated and untreated ewes.…”

“…Surprisingly, 43% (6/14) of trials in this experiment returned a financial loss as a result of treating ewes with a CRC2 pre-lambing. A negative response to CRC administration in ewe liveweight was recorded in 2/10 trials by Gogolewski et al (1997) but otherwise a negative response from use of these products has not been recorded or suggested previously. The variation in cost-benefit was not restricted to CRC, with all the anthelmintic treatments exhibiting a wide variation in response and all having at least some trials where a negative cost-benefit was returned.…”

“…In trials run on 10 commercial farms throughout New Zealand, the mean benefit in ewe liveweight at weaning resulting from administration of an ivermectin CRC prior to lambing, was not significantly different from no treatment at all (Gogolewski et al 1997). A more recent study on three farms in the Manawatu showed a significant response in ewe body condition score, and in lamb liveweight at weaning, resulting from a prelambing injection with doramectin (Cook 2009).…”

Management of gastrointestinal nematode parasites on sheep farms in New Zealand

“…There also appeared to be a tendency amongst farmers to use the same products year after year. Obviously, this refl ected a view by farmers that those products were providing value despite there being little empirical evidence to support this view (Gogolewski et al 1997). Increased selection pressure for resistance has been shown to result from the use of these long-acting formulations given pre-lambing (Leathwick et al 1997(Leathwick et al , 2006aLawrence et al 2006), although in another study no association was evident between their use and the presence of resistance on farms (Hughes et al 2007).…”

“…Perhaps the largest difference between current farmer practices and those recorded in earlier surveys was the widespread use of long-acting products as a pre-lambing treatment to adult ewes. Despite somewhat equivocal evidence for consistent production benefi ts (Gogolewski et al 1997), these products had been used regularly by nearly 50% of the farmers surveyed in the study presented here. The increased use of long-acting products without any decrease in the number of treatments given prompted Leathwick et al (2001) to suggest that parasites are currently exposed to more anthelmintic than ever before, with a corresponding increase in selection for anthelmintic resistance.…”