| Abstrakt: |
The persistent activity of ivermectin long-acting injection (IVM LAI; IVOMEC® GOLD, Merial; 3.15 % ivermectin w/ v) against nematode infections of cattle was evaluated under natural challenge conditions. Seventy nematode-free Brown Swiss calves were blocked by pre-treatment bodyweight and allocated randomly to seven groups of 10 animals each: saline (control) at 1 mL/50 kg bodyweight once on day 0 or IVM LAI at 1 mL/50 kg bodyweight (630 mcg IVM/kg) on either days 0, 7, 14, 21, 28, or 35. After housing until day 35, calves were grazed as one herd on a naturally contaminated pasture for 42 days. Calves were then weighed and housed for 4 weeks before being necropsied for parasite counting. Treatment with IVM LAI prevented the establishment (>90 %, p < 0.05) of Dictyocaulus viviparus (100 %), Bunostomum phlebotomum (100 %), Haemonchus contortus (98.6 %), Ostertagia ostertagi/lyrata (94.9 %), and Oesophagostomum radiatum (93.3 %) for at least 77 days; Ostertagia leptospicularis (99.1 %) for 63 days; Cooperia punctata (97.7 %), Trichostrongylus axei (96.5 %), and Ostertagia spp. inhibited larvae 4 (93.3 %) for 56 days; Cooperia oncophora/surnabada (96.9 %), Trichuris discolor (93.6 %), and Cooperia spp. inhibited larvae 4 (98.8 %); and Nematodirus spp. inhibited larvae 4 (97.1 %) for 42 days. Calves of groups treated with IVM LAI had significantly ( p < 0.001) higher days 0 to 77 weight gains than the saline-treated controls (28.40-39.25 vs 2.60 kg); the weight gains of the IVM LAI-treated groups, however, were not different from one another ( p > 0.3). This study demonstrated a very high efficacy of IVOMEC® GOLD in preventing the establishment of a wide range of bovine nematodes for extended periods of time which was associated with a significant benefit to productivity in terms of weight gain. [ABSTRACT FROM AUTHOR] |
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