Drench resistance in New Zealand sheep

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Sheep

A sheep survey was carried out on 70 farms in the North Island and 42 in the South Island. Of these 112 farms, 32 were chosen because there was suspected or diagnosed ML resistance. The rest were randomly selected.

Testing was undertaken with the three broad-spectrum drench families: Benzimidazole (BZ or white), Levamisole (Lev or clear) and Mectin (Endectocide or Macrocyclic Lactone (ML), e.g. ivermectin, abamectin and moxidectin). A BZ + Levamisole combination and a half-dose ivermectin group were also included.

Results
Overall, 67% of farms surveyed had resistance detected to one or more drench families. Drench resistance was most common for BZs and was least common for a combination of BZ + levamisole. The prevalence of ivermectin resistance was higher than expected.

The good news
These surveys show that drench resistance is a reality, that it is widespread and measures need to be taken to combat it.

The good news is that there are options available. Combination drenches, either dual (BZ + LEV or ML + LEV) or Triple (BZ + LEV + ML) give us effective options on nearly all farms.

By determining the drench resistance status of individual farms and applying what we know about the development of resistance, we have the opportunity to extend the life of the three drench families.

Drench resistance in cattle.

Smart Drenching Tip #11 :

Check drench guns are calibrated and functioning properly.