Make sure the dip that you use on the mob can also kill any freshly hatched maggots. Not all products do this and the IGR group only kills the maggots at their next moult, meaning the freshly struck sheep has to put up with them until then.
Adding something effective to kill maggots to a cyromazine dip is what is done with both Cyrazin KO and Cyrex, for instance. Obviously, if you are ahead of the flies and there is no chance of any struck sheep in the flock, you might choose a product that does not have maggot knock-down like that.
Then, what to do with the struck sheep? Make sure you look hard to identify and draft as many as you can see. Not everyone is good at spotting the early signs, which are subtle.
Struck sheep are not just those with massive areas of stained wool over their rump or down their flanks so make sure everyone is on the same sheet in terms of early identification.
Opinion sometimes differs on what to do with the individual struck animals. One line of thought has been the skin would heal better if the strike was treated but the wool not removed immediately.
We actually suggest a decent clip be done as it makes treated sheep instantly identifiable and tends to leave less scabs with matted wool that may either become infected or even restruck in a few weeks' time. If possible, put those sheep in another paddock, with shade, and feed them as well as you can.
What to treat them with? We suggest a different class of product be used to kill those maggots than the one they may have already been exposed to in the existing sheep dip.
If they managed to get established in the presence of waning quantities of dip in the wool already, why would you try to kill them with the same thing? The commonly used product that actually fits that bill is Maggo, which is an OP.
OP resistance is common but the dips themselves have little use any more, so this is often a good option. Maggo will have very little residual action so dip those animals within a week or so with an effective longer-acting product to avoid a second round of strike.
Another excellent option is Cyrex liquid, which contains spinosad as well as cyromazine, or Extinosad, which is spinosad on its own. These are safer products for humans to handle than OPs and offer a good "change" from what you might normally use. And Cyrazin KO offers an ivermectin component to kill the maggots.
A blanket ban of OPs is on the wish-list of some policy-makers but we had the chance recently to ask that some remain available to help in treatment of fly strike. OPs are not used widely in sheep farming now and it is the best interest of our sheep that we retain this important option to treat in a targeted manner.
- Richard Hilson is a veterinarian with Vet Services (Hawke's Bay) Ltd.
