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SubscribeRefugia is simply the Latin term for ‘in refuge’. When managing drench (anthelmintic) resistance, the aim is to avoid all of the population of worms being exposed to a drench and subject to drench resistance development at the same time. Ideally, part of the population remains unexposed to the drench and is said to be in refugia; it is available to dilute resistant worms so these never become a significant proportion of the farm worm population.
The population of worms on a property is composed of stages within the sheep or goats and stages on the pasture. When pastures are green and temperatures are mild, worms within the animals potentially represent only a minor proportion of the total worm population, but when pastures are dry and temperatures too hot (e.g. summer in Western Australia) or too cold (e.g. winter in the Northern Tablelands of New South Wales) to allow development of worm eggs, then worms within the sheep/goats will represent a very large proportion of the worm population.
The term ‘worms’ is used here to refer to all lifecycle stages of the worm: eggs, larvae, and immature and adult worms. When a drench is given to a mob, the main way that worms within the sheep or goats will be in refugia is when some animals are left undrenched. In contrast, worms on the pasture cannot be exposed to a drench, so are always in refugia. Likewise, on a property basis, worms in mobs not being drenched are in refugia, compared with those in mobs receiving a drench.
Prolonging drench life on a particular property is about slowing the development of drench resistance. The important aspect of drench resistance is the proportion of the worm population (not the number of worms) with drench resistance. Having enough worms in refugia is a powerful way to slow development of drench resistance. Worms in refugia ingested by sheep or goats after a drench will dilute the remaining resistant worms, so these do not become a significant proportion of the total worm population. However, there is a conflict between managing drench resistance and gaining good worm control. Maintaining too many worms in refugia to dilute drench-resistant worms also means more worms to infect goats or sheep after drenching. Nevertheless, with some understanding of when and how to use refugia, you can achieve both good worm control and slower development of drench resistance.
Drench resistance is also specific to a drench group or active family, and to a particular worm species. Benefits from using worms in refugia to dilute resistant worms in drenched animals rely on them being the same species and susceptible to the same drench that was just used.
Translating these principles into action is easy with some forward planning for the following situations where using refugia is beneficial for slowing the development of drench resistance.
NOTE: these strategies have only been trialled in SHEEP flocks.
*Targeted treatment (or ‘targeted selective treatment’) research has been completed in Western Australia and western Victoria, and has been shown to be effective and safe. It has been used successfully by some producers for many years and reportedly has led to a significant reduction in the development of drench resistance. Research has not long been completed and the details of finding the best proportion of the mob to leave in various situations, as well as rules indicating which sheep can miss the drench will be released through WormBoss in early 2017.
Each of the WormBoss Programs includes recommendations on how to use refugia to assist in the management of drench resistance.
Drench resistance can also be managed in a number of other ways. Click here for more information.
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