Blowfly Control in Sheep Flocks

Flystrike is a production limiting, costly and sometimes fatal condition in sheep. When it comes to Blowfly strike the aim should really be to prevent it from happening in the first place. Michael Gottstein, Head of Sheep Knowledge Transfer, Teagasc tells us more.

Flystrike is a production limiting, costly and sometimes fatal condition in sheep. It affects all ages of sheep and is caused when Blowflies lay their eggs on the fleece of a sheep. The flies are attached by soiled areas on the fleece and once the maggots hatch the secrete fluids which attract other flies to lay their eggs on the fleece also.

When it comes to Blowfly strike the aim should really be to prevent it from happening in the first place. There are a number of different options that are available to farmers in this regard.

1) Plunge dipping.

For this process to be effective it is important that the dip solution is made up to the correct strength and that fresh dip concentrate is added into the Dip bath periodically (follow manufacturer’s instructions). The length of time that the sheep remain immersed in the dip solution is strongly correlated to the length of time that protection will last for. For that reason sheep should remain in the solution for a minimum of 60 seconds.

2) Insecticidal pour-ons.

There are a number of Pyrethroid based pour-ons which offer short term cover (6-8 weeks) from flystirke on the areas where they are applied. These products will also kill maggots if they are applied directly to the larvae.

3) Insect Growth Regulators (IGR’s).

IGR’s work by preventing the maggots from developing for the stage one (non feeding larvae) to stage two larvae (feeding – damage causing larvae). Thus the maggots will hatch from the eggs but subsequently die as they are unable to develop to the stage where they can feed on the sheep. There are a number of different products on the market with varying lengths of cover depending on the concentration of the active ingredient. The duration of cover ranges from; Clikzin (upto 8 weeks), Clik (upto 16 weeks) & Clik Extra (upto 19 weeks). All the Clik products have an added ingredient which results in the active ingredient covering the entire body and binding to the lanolin in the fleece so that protection is not only where the product is applied, but in all the wool covered areas. Critical to using these products is that they are applied BEFORE there is any strike. They products do not kill maggots that have already hatched.

4) Shearing

Shearing will provide protection from maggots due to the inability of the flies to attach eggs to the fleece and for the maggots to have protection in the wool. However this protection is only short lived (a number of weeks).

Summary

For season long control the best option is to use a long duration insect growth regulator pour-on. This needs to be applied before sheep are at risk of flystirke and for farmers aiming to sell lambs from the end of June onwards it needs to be applied in mid-May to ensure that the 40 day meat withhold period has elapsed before lambs are ready to draft.

For shorter term control and shorter meat withhold periods use a short acting IGR or Pyrethroid. These will provide 6-8 weeks cover with a 7-8 day meat withhold period.

Where sheep have already been struck or other external parasites also need to be controlled (e.g. ticks, lice etc.) then choose between plunge dipping or a Pyrethroid based Pour – on.

For more information on this topic you can list to our Podcast on the issue – simply scan the QR code on the left with your phone and it will bring you to our series of podcasts called OviCast where you can select the one dealing with blowfly strike.

 Or to watch a short YouTube clip on blowfly control scan the QR code on the right