title: Persistent anthelmintic activity of ivermectin against gastrointestinal nematodes of cattle.
abstract: Two experiments were conducted to determine persistence of ivermectin (IVM) anthelmintic activity. In the first experiment, the injectable (INJ) formulation at a dosage of 200 micrograms/kg of body weight and pour-on (PO) formulation at a dosage of 500 micrograms/kg were compared in 5 groups of calves (n = 6/group). Calves were treated at 14 and 7 days prior to experimentally induced infection. Experimental groups were: 1--untreated, infected controls; 2--IVM PO, day -14; 3--IVM PO, day -7; 4--IVM INJ, day -14; and 5--IVM INJ, day -7. Calves were necropsied on days 28 and 29 after infection. Results of this experiment indicated a high degree of efficacy of IVM PO product (93.8%) for all nematodes up to 14 days, in contrast to poor activity for IVM INJ (26.3%) for all nematodes. Seven-day persistence was excellent for both IVM formulations against Ostertagia ostertagi and Cooperia spp, but a lower degree of efficacy (77.0% for PO and 88.5% for INJ) was observed against Haemonchus placei. In the second experiment, persistent efficacy of IVM PO in preventing establishment of O ostertagi inhibited larvae was observed. In 3 trials, groups of 4 treated and 4 untreated control calves were exposed to natural pasture infection at 0 to 7, 10 to 17, and 20 to 27 days after treatment. Calves were necropsied 15 to 16 days after removal from pasture. After the day 0 to day 7 infection exposure, IVM PO efficacy was 100% for all stages of O ostertagi, 3 adult male Cooperia spp, and Oesophagostomum radiatum; 94.9% for H placei; and 98.2% for Cooperia spp adult females.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000018:Abomasum / Q000469:parasitology*; D000284:Administration, Oral; D000818:Animals; D000969:Antinematodal Agents / Q000008:administration & dosage / Q000627:therapeutic use*; D002417:Cattle; D002418:Cattle Diseases; D005767:Gastrointestinal Diseases / Q000469:parasitology / Q000517:prevention & control / Q000662:veterinary*; D006188:Haemonchiasis / Q000517:prevention & control / Q000662:veterinary; D006189:Haemonchus / Q000302:isolation & purification; D007279:Injections, Subcutaneous; D007559:Ivermectin / Q000008:administration & dosage / Q000627:therapeutic use*; D008297:Male; D009349:Nematode Infections / Q000517:prevention & control / Q000662:veterinary*; D010028:Ostertagia / Q000302:isolation & purification; D010029:Ostertagiasis / Q000517:prevention & control / Q000662:veterinary
chemical_list: D000969:Antinematodal Agents; D007559:Ivermectin