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


METHODS
24 mixed-breed sows.


METHODS
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 micrograms 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.


CONCLUSIONS
Ivermectin fed to sows during the last third of gestation at a dosage of 100 micrograms/kg/d for 7 consecutive days is highly efficacious for control of transmission of infective S ransomi larvae to pigs via colostrum or milk.
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Worldwide Clinical Operations Division of Merial Ltd, Merck & Rhône-Poulenc Co, Fulton, MO 65251, USA.
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D000818:Animals; D000969:Antinematodal Agents / Q000008:administration & dosage / Q000627:therapeutic use*; D003126:Colostrum / Q000469:parasitology; D019587:Dietary Supplements; D005260:Female; D018445:Infectious Disease Transmission, Vertical / Q000517:prevention & control / Q000662:veterinary; D007559:Ivermectin / Q000008:administration & dosage / Q000627:therapeutic use*; D007814:Larva / Q000187:drug effects; D008892:Milk / Q000469:parasitology; D010270:Parasite Egg Count; D011247:Pregnancy; D015597:Pregnancy Complications, Parasitic / Q000517:prevention & control / Q000662:veterinary*; D013321:Strongyloides / Q000187:drug effects / Q000254:growth & development / Q000302:isolation & purification*; D013322:Strongyloidiasis / Q000517:prevention & control / Q000662:veterinary*; D013552:Swine; D013553:Swine Diseases
D000969:Antinematodal Agents; D007559:Ivermectin