Efficacy of levamisole against Ostertagia ostertagi in Louisiana cattle during maturation of inhibited larvae (September) and during minimal inhibition (December/January)

摘要: Abstract Levamisole (LEV) was tested in four experiments to compare efficacy values against Ostertagia ostertagi when larval maturation occurring (September), following inhibition and also populations were expected be largely adult (winter). A primary objective determine the importance of developing fourth-stage larvae (DL4) inhibited, early (EL4) replacing worms lost through treatment effect this on reduced worms. Young crossbred beef calves ranging weight from 150 230 kg used first (September 1981), second 1983) third (January 1987). Jersey 110 average fourth experiment (December 1988). Calves randomized groups according group sizes ranged three five calves. All parasite infections naturally acquired, but a mixture nematode third-stage (L3) (22 500 per calf), including 20% ostertagi, inoculated into Experiment 4 2 week exposure natural infection. LEV treatments by subcutaneous injection at dosages 6 8 mg kg−1. Treatment with ivermectin only 3 as an reference. killed 8–10 days after treatment. The all developmental stages consistently low dose-dependent response not evident. Large numbers present non-treated both September experiments. Percent reduction adults, DL4 EL4 kg−1 dosages, respectively, 51.7 23.6 (1981), 8.7 51.3 (1983); 40.3 13.2 37.9 33.1 EL4, 19.6 0 59.6 42.9 (1983). Smaller winter greatly outnumbered stages. reductions (1987) kg−1, 40.2, 0; 200 μg 98.7, 97.7 100.0; (1988) 62.4, 100.0 49.1 65.0 74.1. Too few latter for valid values. Data suggested that could have replaced adults based progressive September, slightly treated compared controls, particularly 1981, increased proportion young female without eggs LEV-treated 2. consistent activity some degree resistance across stages, proven