Comparison of the anthelmintic effectiveness of six commercial products containing macrocylic lactones against bovine gastrointestinal nematodes

Abstract

The study was carried out from April to July 2001 on a cattle farm located in the south of Chile (lat. 40º- 53S, long. 70º - 44O). Naturally infected bovine of 280 kg average body weight were distributed in 7 groups (n = 12): control group (placebo), and 6 groups treated subcutaneously with 0.2 mg/kg of Ivermectin (3 groups with different commercial products), Moxidectin, Abamectin and Doramectin. Individual faecal samples were obtained from all animals 3 days prior to, on the treatment day and then, weekly until the 77 days post-treatment (p.t.). Individual egg-counts (epg), faecal egg reduction test and accumulative larvae cultures per group were carried out.. The pasture contamination was determined on days 0, 14, 56 and 77 p.t. Individual body weight on days –3 and 63 p.t. was recorded. The results were analysed considering significant p < 0.05.

The control group presented mean egg counts fluctuating between 140 and 500 epg. The 6 treated groups showed a significant reduction of the epg until day 42 p.t. In the groups treated with Moxidectin, Abamectin and Doramectin there was a significant reduction up until days 63 and 77 p.t. Anthelminthic resistance were found for all products, excepting Doramectin at day 21 p.t. Persistence of effectiveness until 14, 28 and 35 days were found for the products with Ivermectin, 42 days for Moxidectin and Abamectin and 49 days for Doramectin. Until day 63 p.t., all treated animals weighed 15.1 kg more than the control animals (p < 0.05). It was concluded that the products showed differences in their effectiveness and persistence.