Abstract

Worm anthelmintic resistance is entering the final phase, where nothing remains with which to control worms at a level commensurate with profitable animal production. In Brazil, for instance, moxidectin alone or in combination with other compound(s) has failed in numerous cases in sheep and goats, and in New Zealand combined treatment of goats with moxidectin plus a benzimidazole and levamisole failed completely against Trichostrongylus and Ostertagia spp. Cattle follow closely behind, with a recent survey in Argentina indicating a prevalence of 55 % of worm populations resistant to ivermectin. It is suggested that the solution for sustainable Integrated Parasite Management is use of systems of Targeted Selective Treatment (TST) to optimise application of the phenomenon of refugia for reduced worm selection. However, due to reticence of farmers and their advisors, the required major paradigm shift will be very difficult to achieve. To overcome this, it is suggested that dedicated software be developed for specific decision support at farm level, as detailed as the intervals between TST evaluations of a given flock/herd of animals and percentages of animals to examine and treat. The conclusion reached is to face the fact that no excuse regarding animal production or farmer reticence will expunge the reality that conventional worm control is leading to intractable resistance; optimum, not maximum production is the prerequisite.

JA, Van Wyk

Proceedings of the New Zealand Society of Animal Production, Volume 66, Napier, 4-13, 2006