Efficacy of an in-feed formulation of ivermectin against somatic larvae of Strongyloides ransomi in pregnant swine

Marlene D. Drag From Pharmaceutical Research & Development, Worldwide Clinical Operations Division of Merial Ltd, a Merck & Rhône-Poulenc Co, 6498 Jade Rd, Fulton, MO 65251.

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Sara E. Green From Pharmaceutical Research & Development, Worldwide Clinical Operations Division of Merial Ltd, a Merck & Rhône-Poulenc Co, 6498 Jade Rd, Fulton, MO 65251.

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Russell A. Howser From Pharmaceutical Research & Development, Worldwide Clinical Operations Division of Merial Ltd, a Merck & Rhône-Poulenc Co, 6498 Jade Rd, Fulton, MO 65251.

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Dennis H. Wallace From Pharmaceutical Research & Development, Worldwide Clinical Operations Division of Merial Ltd, a Merck & Rhône-Poulenc Co, 6498 Jade Rd, Fulton, MO 65251.

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James L. Cox From Pharmaceutical Research & Development, Worldwide Clinical Operations Division of Merial Ltd, a Merck & Rhône-Poulenc Co, 6498 Jade Rd, Fulton, MO 65251.

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Ruth A. Barrick From Pharmaceutical Research & Development, Worldwide Clinical Operations Division of Merial Ltd, a Merck & Rhône-Poulenc Co, 6498 Jade Rd, Fulton, MO 65251.

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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)

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)

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