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Resistance to drench is a growing problem on NZ farms and is a serious issue for farmers due to the cost and irreversible nature of resistance.

Drench resistance costs

  • There is a significant cost attached to the lost productivity as a result of drench resistant worms. Drench resistance is estimated to cost New Zealand sheep farmers an additional $20 million a year on top of the $300 million annual cost of internal parasites in lost production and drench use[1]. This cost is expected to rise as drench resistance becomes more prevalent.
  • A recent New Zealand study estimated the presence of drench resistance resulted in a 14% reduction in carcass value[2].
  • At a farm level a 5% loss in lamb growth on a 3,000 ewe breeding operation could cost over $15,000 in lost productivity.

Drench resistance is widespread

  • A 2006 study [3] of over 80 randomly selected farms showed 64% had resistance to Albendazole, 25% to Ivermectin and 24% to Levamisole.
  • This study of NZ farms found that 64% of farms had resistance to one or more drench actives, which are those in currently available double and triple combinations.
[1] Risk factors for drench resistance in sheep. January 2008 - Issue 4, Wormwise

[2] The production costs of anthelmintic resistance in sheep managed within a monthly preventive drench program; I.A. Sutherland, J. Shaw, R.J. Shaw. 2010. Veterinary Parasitology.

[3] Prevalence of anthelmintic resistance on sheep farms in New Zealand. Waghorn,T.S.et al: N ZVJ 54: 271-277, 2006.

* As determined by Farmax modelling.