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1. Which drench group does moxidectin belong to and what other drench actives are in this group?
2. True or false: Diazinon is still highly effective against both lice and flies.
3. How many months could it take for a new lice infestation to become evident?
4. Will worms in goats develop resistance to drenches at the same rate as those in sheep?
Image: Lucilia cuprina third stage larvae (cream) and pupae (red). Source: Geoff Brown, DAF Qld.
Drench Group: Macrocyclic lactones (ML) or "mectins".
Other drench actives in the group: ivermectin, abamectin (there are others, but not in sheep or goat products)
False: While Diazinon is still highly effective against lice, resistance is extremely common in flies. Maggots, particularly the bigger/older maggots, are often not killed by Diazinon. However, when wool is shorn from and around a strike wound, removing most of the maggots, diazinon-based preparations generally provide sufficient protection against restrike during the healing process.
It is generally at least 3 months and up to 6 months before a new lice infestation can be detected by seeing rubbed wool and finding actual lice.
The time depends on the amount of lice introduced, e.g. from one lightly lousy stray in the mob a short time, to introduction of a large number of quite lousy sheep into a mob permanently.
Worms in goats are likely to develop resistance to drenches at a faster rate. Goats metabolise drenches at a faster rate thereby exposing the worm to a lower dose for a shorter period of time. The effect is like receiving a lower dose of drench, which can allow not just existing drench resistant worms to survive, but also the partially resistant worms that would have otherwise been killed by exposure to a full dose for a longer period.
In the field, many of the earliest cases of drench resistance to new drenches have occurred in goats, rather than sheep.
Goat producers need to contact their veterinarian for advice and a prescription (as this is off label use) for appropriate dose rates of sheep drenches for goats. These dose rates will vary according to the particular drench active, and caution should be taken because too large a dose of some actives may result in toxicity in goats.