Objective To investigate the therapeutic and prophylactic efficacy of an ivermectin controlled‐release capsule against nasal bots (Oestrus ovis) in sheep.
Design Trial 1 – A pen study with controls. ...Trial 2 – A field study with controls.
Animals Trial 1 – Forty Merino wethers with natural infestations of nasal bot were used. Trial 2 – One hundred nasal bot‐free wethers were used.
Procedure Trial 1 – Ten randomly selected animals were slaughtered and the heads split and examined to confirm bot infestation. Fifteen animals were allocated to untreated controls and 15 to treatment with a controlled‐release capsule delivering ivermectin at ≥ 20 μg/kg/day for 100 days. Twenty‐nine days after treatment the sheep were killed and examined for nasal bots. Trial 2 – Nasal bot‐free sheep were allocated to two groups of 45 animals. One group was untreated the other sheep were treated with capsules as above. The sheep were grazed as a single group exposed to natural challenge from O ovis. Ninety days after treatment the animals were slaughtered and examined for nasal bot infestation.
Results Trial 1 – Live O ovis larvae were recovered from 60% of control sheep. No live larvae were collected from treated sheep. Trial 2 – Forty‐one percent of untreated sheep harbored nasal bot infestations. No live larvae were collected from any treated animal.
Conclusion Treatment with a single ivermectin controlled‐release capsule was 100% effective against existing infestations of O ovis and as a prophylactic treatment for this parasite.
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 20 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 ivermectin controlled-release capsule gained on average I.I kg 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.
Antigenic relatedness between the virion-associated proteins of caprine arthritis-encephalitis, visna and progressive pneumonia viruses was examined. Antigenic cross-reactivity was assessed by ...immunoprecipitation of disrupted, radiolabelled virus with goat, sheep and rabbit antisera, followed by resolution of the immunoprecipitation products by SDS-polyacrylamide gel electrophoresis. The results indicate that antigenic cross-reactivity between the caprine and ovine virus isolates involves all of the major virion-associated proteins and glycoproteins. The common antigenic determinants exhibited by virion structural proteins are immunogenic in goats, sheep and rabbits.
To confirm the efficacy of ivermectin released from a controlled-release capsule administered to young sheep and to breeding ewes under field conditions.
Randomised field trials.
In each of ten field ...trials 25 weaned lambs were treated with ivermectin controlled-release capsules and 25 remained untreated. Eight similar field trials were conducted using adult ewes. Efficacy against infections of gastrointestinal nematodes was assessed by faecal egg counts and faecal larval culture. Body weights were recorded and faecal soiling of the breech wool (dags) was assessed.
Nematode faecal egg counts in the two groups were not different (P = 0.13) before treatment in the weaner trials or before treatment in the ewe trials (P = 0.49), but thereafter eggs in the untreated sheep persisted, whereas counts in sheep given capsules were negligible (P < or = 0.01). In the weaner trials, dag scores for the two groups were not different at the start of the trials (P = 0.18) but at the end, untreated sheep had significantly more dags (P = 0.04) than treated sheep. In the ewe trials, dag scores remained low in both groups. Weaners treated with the capsule gained 1.4 kg (95% CL: 0.7, 3.1) more weight over the 16 week trial period compared to untreated weaners (P = 0.01). Both groups of ewes lost weight as a result of parturition but the mean loss by week 16 was greater for untreated (3.7 kg) (95% CL: -5.1, -2.2) than for treated ewes (1.8 kg) (95% CL: -3.3, -0.4). The mean change in ewe body weight for the two groups was however not significant (P = 0.07). Differentiation of nematode larvae recovered from cultures of faeces from untreated animals indicated that the capsules were effective against the common parasites of sheep.
The capsule was efficacious against gastrointestinal nematodes judging from faecal egg counts. It has the potential to significantly reduce contamination of pasture with nematode eggs. Treated weaners had less dags for 16 weeks and gained more weight than untreated weaners.
Ten field trials were conducted in the North and South Islands of New Zealand to evaluate the anthelmintic efficacy and production responses attributable to treatment of weaner lambs with an ...intra-ruminal controlled-release capsule formulation of ivermectin. A total of 800 Coopworth, Perendale and Romney lambs weighing on average 20.8-34.8 kg were used. Lambs were either untreated or treated shortly after weaning with an ivermectin controlled-release capsule which delivers ivermectin at 0.8 mg per day for 100 days (minimum dose rate 20 g/kg/day). Bodyweights, faecal nematode egg counts and dag scores (assessment of faecal soiling in the breech area) were determined before treatment and at about 4, 8, 12, 14 and 16 weeks after treatment. Sheep treated with the ivermectin capsule gained significantly more weight (11.6 kg) over the 16 weeks of the trials compared to untreated sheep (7.3 kg) (p < 0.01). Before treatment, faecal strongylid and Nematodirus spp. egg counts were equivalent (p > 0.10) but, at each time point thereafter, egg counts in ivermectin capsule-treated sheep were significantly lower (p < 0.01 or p < 0.05). Dag scores were not different at the start of the trial (p > 0.10), but at the end of the trial control sheep had significantly greater dags (p < 0.05) than sheep treated with the ivermectin capsule. These findings indicate that treated animals contributed significantly fewer nematode eggs to the contamination of pasture and therefore pasture contamination should be significantly reduced for at least 112 days. The productivity of the ivermectin capsule-treated sheep over the 16 weeks of the trials was also significantly increased compared to salvage-treated controls. Furthermore, the presence of dags, which predispose sheep to blowfly strike in the breech area and result in production losses due to the costs of dagging and downgrading of breech wool, were also significantly (p < 0.05) reduced in the ivermectin capsule-treated sheep.
The efficacy of ivermectin delivered by an intraruminal controlled-release capsule against gastro-intestinal nematodes of sheep was evaluated under controlled conditions. In seven Australian studies ...involving 170 Merino or Merino × Border Leicester sheep, intraruminal capsules developed for 20-40 kg or 40-80 kg sheep, and delivering 0.8 or 1.6 mg of ivermectin/day respectively for 100 days (minimum dose 20 μg/kg/day), were evaluated. Studies were designed to test the therapeutic efficacy against naturally acquired and induced infections treated at the adult and fourth larval stage, and the prophylactic efficacy against naturally acquired and induced infections with third stage infective larvae. The predominant pathogenic nematodes of sheep were represented. Two studies included known benzimidazole- and levamisole-resistant nematode strains. Sheep were necropsied for total nematode counts 21-8.5 days after treatment. The efficacy of the ivermectin controlled-release capsule was generally >99% against all nematode species tested, including those confirmed to be benzimidazole- and levamisole-resistant. High therapeutic activity was demonstrated against existing adult and fourth larval stage nematode infections at the time of treatment, and high prophylactic efficacy was shown against incoming third stage larvae of all species and strains tested.
Objective To investigate the efficacy of ivermectin in an intraruminal controlled‐release capsule (CRC) against blowfly strike.
Design Pen and 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 in Australia.
Procedure Pen studies: Sheep were allocated to two equal groups. One was not treated, the other sheep received a CRC that delivered ivermectin at 20 μg/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).
Conclusion The ivermectin CRC is a useful aid in controlling breech strike, but provides only moderate reduction in the incidence of body strike.
Objective To compare haematological values and lymphocyte phenotypes in the peripheral blood of fleece rot‐resistant and ‐susceptible sheep.
Procedure Experiments were conducted on 2‐ and 3‐year‐old ...Merino rams, flock 1 (17 rams) and flock 2 (32 rams), respectively. Within each flock, individual rams were classified as fleece rot‐resistant or ‐susceptible, based on established criteria. Total and differential white cell counts, and indirect fluorescent antibody tests specific for B cells and T cells were performed on all sheep. The concentration of various subsets of circulating lymphocytes was then determined in each sheep.
Results There were no significant differences between fleece rot‐resistant and ‐susceptible sheep from either flock in the mean total or differential white cell counts. However, fleece rot‐resistant rams in flock 1 did have a significantly higher concentration of circulating SBU‐T1+ cells than fleece rot‐susceptible rams from the same flock. No such difference was noted in the rams from flock 2. While all rams in flock 1 were free of clinical fleece rot, 24 rams in flock 2 (comprising all 17 fleece rot‐susceptible and 7 of 15 fleece rot‐resistant animals) had clinical signs of the disease. Fleece rot‐free rams in this flock (irrespective of their classification as fleece rot‐resistant or ‐susceptible) had significantly higher concentrations of circulating SBU‐T1+ cells compared with fleece rot‐affected animals. They also had significantly higher concentrations of circulating B cells, and total lymphocytes.
Conclusions An examination of peripheral blood lymphocyte subsets in fleece rot‐resistant and ‐susceptible sheep revealed a possible association between resistance to fleece rot and the concentration of circulating SBU‐T1+ cells.
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