HOW COMMON IS DRENCH RESISTANCE?

All farms in New Zealand have some resistant worms. It is impossible to tell exactly what percentage of worms on a farm have resistance genes, so faecal egg count reduction tests (FECRT) are used to estimate resistance status.

Recent surveys have indicated that detectable drench resistance is widespread (see Table 1 below). A study funded by Meat and Wool New Zealand, the MAF Sustainable Farming Fund and Intervet/Schering-Plough Animal Health Ltd. profiled anthelmintic resistance and parasite control practices on sheep and cattle farms throughout New Zealand^{[1, 2]}.

Drench resistance in cattle.

Drench resistance in sheep.