Refugia-based drenching regimes have been widely recommended to slow development of anthelmintic resistance, but there are few comparisons between different treatment approaches in the United Kingdom.
Over a five year period, researchers compared efficacy of four different treatment regimes in anthelmintic (ivermectin) efficacy, body weight, and pasture contamination in lambs naturally-infected with gastrointestinal nematodes in Scotland.
Regimes were whole flock treatment every 4 weeks (NST), targeted selective treatment (TST) based on performance, strategic whole flock treatments at predetermined times (SPT), and whole flock treatment when clinical signs were apparent (MT).
Overall, both the TST and SPT regimes appeared to maintain animal performance and conserve anthelmintic efficacy compared with a neo-suppressive anthelmintic treatment regime.
Conclusion: Comparison of four different anthelmintic treatment regimes on the efficacy of ivermectin showed that regular monthly administration of anthelmintics to all lambs in a group does result in reduced drug efficacy. Further, the provision of refugia, regardless of how it is produced, does assist in slowing the decline in drug efficacy and anthelmintic regimes that provide an acceptable balance between the provision of refugia and animal performance can be achieved in a temperate grazing environment.
Read full article in International Journal for Parasitology: Drugs and Drug Resistance (2013)