Flystrike challenge normally occurs from November through to March during the warm humid conditions that favour the rapid increase in blowfly populations.

Blowflies lay eggs on the fleece (usually down the mid back and crutch areas) which hatch into maggots. The maggots burrow into the flesh. This is easily prevented with the use of a fly strike prevention pour on and will save your stock from the unpleasant effects of fly strike.

Early signs of flystrike include irritation such as stamping, tail twitching, rubbing and biting the affected area. Sheep or particularly lambs can die from fluid and protein loss from the wound or septicaemia.

A struck sheep should be dealt with immediately. The wool around the struck area should be cut away ensuring good clear margins and the area sprayed with a strike treatment product and/or antibiotics. Note not all preventative products can kill maggots/flies immediately.

There are many products available for fly strike prevention all with different modes of application, length of action and withholding periods. Contact your nearest clinic for help in choosing one which will best suit your needs.

Preventing flystrike in sheep involves several strategies:

  1. Prevent dags around the crutch/breech area especially lambs
    • Docking lambs
    • Crutch or shear sheep in Summer
    • Have a good worm control strategy
  1. Remove potential fly breeding grounds- organic waste/effluent areas where breeding of fly can occur
    • Burn or bury deeply any dead animals (including sheep, rabbits, opossums) on the farm; cover offal pits; avoid creating dung heaps or composting vegetation.
    • Keep sheep away from high risk areas. Blowflies love sheltered areas such as scrubby gullies. They dislike windy exposed areas.
  1. Chemical prevention – insecticides or insect growth regulators (IGR’s)

There are several different chemical families used to prevent fly strike; and they are applied in different ways. Application can require saturation on the sheep fleece to skin level (plunge or shower dips); pour-on or spray-on application to the back and breech of the sheep; or hand jetting (the most effective and economical). The chemical used will depend on the method of application, the length of time of protection required, and whether lice treatment is required as well as fly protection.

Treatment for Lambs

For lambs we would recommend a product with short/medium term protection such as Cyromazine e.g  Cyrazin®Spray-On. Meat Withhold 14d or Cyrazin®Liquid as a dip, shower or jet for medium-long term protection and a shorter 7d Meat Withhold.

Ewes

For replacement stock or breeding ewes a pour-on or spray-on IGR’s with Triflumuron e.g. Exit®/Zapp® Encore or Dicyclanil e.g. Clik®are more convenient to apply and have a longer persistency. However Meat Withhold 49/56 days and 35 days respectively.

Resistance

Resistance has been reported to many actives in the upper North Island and it may be prudent to consult with your veterinarian. But before you consider resistance it is very important to read the label in full and follow the manufacturer’s directions for use.

David McDonnell  BVSc, MANZCVSc