Friday, June 15, 2012

The cost of anthelmintic resistance

Researchers in New Zealand were able to measure the economic impact of anthelmintic resistance by comparing productivity parameters in groups of lambs treated with either a highly effective anthelmintic or an anthelmintic which three species of resistant worms were known to be present.

Ten farmlets, each stocked with 30 lambs, were rotationally grazed for five months, with monthly treatments of either albendazole (Valbazen®), to which resistance existed, or a new combination product containing derquantel and abamectin (DQL–ABA), to which there was no resistance.

Anthelmintic efficacy was measured at the last two treatment dates by fecal egg count reduction test with larval cultures. Albendazole demonstrated efficacies of 48.4% and 40.9% for Trichostrongylus spp. and Teladorsagia circumcincta respectively. By contrast, the DQL–ABA treatments were > 99% effective against all genera.

The difference in live-weight gain was 9 kg (19.8 lbs.) in favor of the DQL–ABA treatments. Significant differences in body condition scores, fecal breech soiling and fleece weights were also recorded, all in favor of the DQL–ABA treatments. The time required for 50% of the animals to reach a target live-weight of 38 kg (83.6 lbs.) was significantly shorter (by 17 days) in those animals treated with DQL–ABA.

The production cost of using an anthelmintic which is not achieving the expected levels of efficacy due to anthelmintic resistance was clearly demonstrated. The loss of productivity due to sub-clinical parasitism was also demonstrated by these results.

Source:  Veterinary Parasitology, May 2012.
Read full article at Science Direct

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