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SUMMARY

Twelve calves (mean weight, 175.5 kg) were used to confirm efficacy of ivermectin delivered from a prototype sustained-release bolus against naturally acquired gastrointestinal nematodes including early fourth-stage (inhibited) larvae of Ostertagia ostertagi. The calves were allocated by restricted randomization on weight to 1 of 2 groups: controls, to which a placebo bolus was given orally, and treated calves, to which a sustained-release bolus designed to deliver 8 mg of ivermectin/day at a steady rate was given orally. After treatment, the 2 groups were housed in separate pens with concrete flooring. Twenty-eight days after treatment, all calves were euthanatized and necropsied. The ivermectin-treated calves had no larval or adult Ostertagia spp and significantly (P < 0.01) fewer adult Trichostrongylus axei and adult Cooperia (C oncophora, C punctata and C surnabada) than control calves. Efficacy of ivermectin was > 99% for Cooperia spp, and 100% for other parasites. Drug-related adverse reactions were not observed.

Free access
in American Journal of Veterinary Research

Objective

To assess parasite control and weight gain after administration of an ivermectin sustained-release bolus over 135 days to calves grazing in the midwestern United States.

Design

Replicated pasture study.

Animals

56 Bos taurus calves.

Procedure

Calves were matched for body weight and randomly allocated to remain untreated or to receive an ivermectin sustained-release bolus before turnout on day 0. Calves were grazed by treatment group on 8 pastures (4 replicates). Body weights and fecal egg counts were recorded on days −1 and 28, and then at 28-day intervals until day 168.

Results

Parasitism was not clinically evident prior to or during the study. In treated calves, mean fecal egg counts were at or near 0 at all posttreatment evaluations. Although the mean egg count exceeded 20 ova/g only once in control calves, the cumulative egg output was > 42 million/calf. For the treated group, it was < 0.1% of this number. Mean total weight gain was 33.9 kg (74.6 lb) greater for ivermectin-treated calves than for untreated control calves (P < 0.02); a 34% increase.

Clinical Implications

Fecal trichostrongyle eggs from calves can accumulate over a grazing season to provide enormous potential for augmenting pasture infectivity. An ivermectin sustained-release bolus (administered to calves being placed on pasture) controls parasitism, limits pasture infectivity, and can substantially influence growth by limiting the impact of subclinical parasitism. (J Am Vet Med Assoc 1997;211:754–756)

Free access
in Journal of the American Veterinary Medical Association

Abstract

Objective

To confirm that ivermectin fed for 7 days to pregnant sows controls transmission of Strongyloides ransomi larvae to pigs via the colostrum or milk.

Animals

24 mixed-breed sows.

Procedure

The sows were infected with 250,000 S ransomi larvae on 3 occasions (days 63, 64, or 65, days 71 or 73, and days 78, 79, or 80 of gestation). Eight sows received ivermectin at a dosage of 100 μg of ivermectin/kg of body weight/d from days 92 to 99 of gestation, and 8 sows were treated from days 103 to 110 of gestation; 8 remaining sows received unmedicated vehicle. Numbers of S ransomi larvae were counted in samples of colostrum or milk collected 1, 2, and 7 days after parturition. At 7 and 14 days after parturition, fecal samples were collected from each sow and from 4 pigs from each litter for determination of nematode egg counts; at the latter date, pigs were euthanatized and necropsied for worm counting.

Results

Pigs born to ivermectin-treated sows had significantly (P < 0.01) fewer adult S ransomi than did those born to control sows; efficacy was 100%. Treated sows had significantly (P < 0.05) fewer S ransomi larvae in colostrum/milk samples taken 1, 2, and 7 days after parturition than did control sows; efficacy was 100%, with the exception of 1 S ransomi larva found in a milk sample from 1 treated sow at 2 days after parturition.

Conclusion and Clinical Relevance

Ivermectin fed to sows during the last third of gestation at a dosage of 100 μg/kg/d for 7 consecutive days is highly efficacious for control of transmission of infective S ransomi larvae to pigs via colostrum or milk. (Am J Vet Res 1998;59:277–279)

Free access
in American Journal of Veterinary Research

SUMMARY

One hundred four heartworm-free Beagles < 1 year old were studied to determine the efficacy of ivermectin chewable tablets and of 2 other ivermectin tablet formulations against heartworm larvae. At 30 days after sc inoculation of dogs with infective Dirofilaria immitis larvae, all ivermectin formulations were given orally at dosage of 6 μg/kg of body weight. The ivermectin chewable tablets also were given orally at dosage of 2 and 6 μg/kg at 30 and 45 days, respectively, after injection of larvae. Replicates of 6 or 8 dogs in each study were formed on the basis of gender and body weight and, within replicates, were randomly allocated to treatment groups. At 30 days after injection of larvae, the additional dogs (in replicates of 8) were assigned to the control group and to the group given ivermectin chewable tablets at dosage of 6 μg/kg. All dogs were housed individually. Necropsy was performed approximately 5 or 6 months after larvae were administered.

In both trials, all control dogs had heartworms at necropsy (Univerity of Illinois—geometric mean, 35.0; Florida—geometric mean, 26.1). In both trials, the ivermectin chewable tablet (6 μg/kg) and both tablet formulations (6 μg/kg) given at 30 days after larval injection, and the chewable formulation (6 μg/kg) given at 45 days after larval injection were 100% effective (P < 0.01) in preventing development of induced infection with D immitis. Of 8 dogs at the University of Illinois that were given ivermectin chewable tablets (2 μg/kg) at 30 days after larval injection, 6 had heartworms (geometric mean, 2.25; efficacy, 93.6%; P < 0.01) and 5 of 7 dogs treated similarly in Florida had heartworms (geometric mean, 4.4; efficacy, 83.3%; P < 0.05).

Drug-related adverse reactions were not observed in either trial.

Free access
in American Journal of Veterinary Research