Home > The issues > Flystrike

What is flystrike?

Flystrike is when a blowfly lays eggs in the fleece of the sheep and the eggs hatch into larvae that in turn become maggots. These maggots then eat into the skin and tissue of the sheep. Flystrike can produce inflammation, general systemic toxaemia, and even death. Flystrike can happen anywhere on the body but is most likely to happen underneath the tail of lambs and sheep.  Merino Sheep are now bred to have more wrinkly skin to increase the amount of wool so that creates a higher chance of fly strike. 

It is estimated that around 3 million sheep a year die as a result of flystrike in Australia (Wardhaugh and Morton, 1990). Many more are affected by non-fatal strikes [1]  

 

What types of flystrike are there?

There are various types of flystrike which can occur on a sheep. Breech strike and body strike are the most production-limiting types affecting Victorian producers. Flystrike can occur at various locations on sheep, including:

  • Breech strike; taking place around the crutch area of the sheep, due to urine and faecal stains causing skin irritation and the weeping of fluids, providing a protein source for flies
  •  Body strike; fleece infected with fleece rot or other forms of bacterial stain. 
  • Wound strike; a protein-producing moist area caused by any type of wound to the skin e.g. footrot or marking. 
  • Pizzle strike; scalding of skin and weeping fluid around the pizzle cause by urine stained wool. 
  • Poll strike; affecting the base of horns in rams or wethers as a result of wounds or sweat [2]

 

What environmental factors creating high risk periods for flystrike [2]

  1.       Moderate to low wind speeds, as fly numbers increase as wind velocity decreases.
  2.       Warm day following rain if the sheep have got wet and the fleece is moist
  3.       There is continual wetting of fleece, without drying promoting bacterial growth.

 

Alternatives for the prevention of Flystrike

Mulesing does not eliminate the incidence of flystrike and flystrike may also occur on areas of the sheep other than the mulesed area. 

Melbourne Sheep Save agrees with the below points that originate from The Victorian Farmers Federation list of prevention methods for flystrike [3].

  1. Commercial producers are able to select specific traits for breeding, which decreases the risk of flystrike in the flock. This reduces the susceptibility of sheep by concentrating on the traits that predispose sheep to breech strike (wrinkle and dag) and body strike (fleece rot). 
  2. If a preventative chemical is not used, sheep should be inspected every two days during high risk periods. 
  3. Apply a range of husbandry practices to manage dag and flystrike risk such as shearing, crutching, worm control and nutrition practices (to bind faecal material). 

Although Melbourne Sheep Save does not support the farming of sheep for profit, it does, however, agree with the position of The Australian Wool Innovation that recommends the selective breeding for sheep that are less susceptible to flystrike [4]. 

Melbourne Sheep Save also agrees with their stance on the removal of mulesing and the promotion of the use of other preventative measures such as double crutching, accelerated shearing, shorter lambing periods and increased use of contract labour. 

 

Treatment for flystrike

Flystrike, if it occurs, is a treatable condition that does not necessarily result in the death of the sheep. The following paragraphs describe the treatment of flystrike in sheep on a farm animal sanctuary and the method recommended by the Victorian Farmers Federation. The former being applicable to a situation where the number of sheep is less and each sheep can be cared for on an individual basis. The latter is applicable to mega farming situations in which labour, time and money are often in short supply. 

 

Treatment in a sanctuary situation

  1. Wipe away maggots with a warm wet cloth, can slightly wet or dampen the cloth in with some iodine and water
  2. Many maggots will fall out with the wiping but if not all are removed apply water pressure with a 20 ml or 50ml syringe or even a hose as the maggots may have dug in too far for wiping to be effective
  3. Spray generously with Extinosad 
  4. Check the rest of the sheep for maggots
  5. Treat sheep with antibiotics in case of infection and pain relief
  6. Check again 24 hours later
  7. If you see your sheep/lamb has a cut or abrasion spray with Extinosad after cleaning immediately.
  8. Cut away any dirty wool from the bottom area, maggots can also live in the wool.
  9. In severe cases a course of antibiotics may be needed.

 

Treatment recommended by the Victoria Farmers Federation  [2]

Treatment treating flystruck sheep is essential. If struck sheep are left untreated or incorrectly treated then sheep can suffer significant stress, produce tender wool, become vulnerable for restrike by a secondary blowfly species or death may occur. During periods of high risk it is important to check susceptible stock regularly. Often by the time flystruck sheep are found the maggots have completed their development. These maggots must be killed to stop them from becoming the next generation of blowflies that cause strike. 

General principles for treating flystruck sheep include:

  • Removal of struck wool. Clipping the wool allows for the infected skin to dry out as well as exposing maggot trails.
  • Clipping should extend 4-5cm into clean wool to ensure all maggot trails have been exposed.
  • Clipped wool should be placed in a plastic bag, sealed and left to dry out in the sun, thus killing the maggots.
  • Dressing should be thoroughly applied to the infected area using a registered chemical. This prevents the area from being restruck while it is healing

Animals Australia states that: “Very careful husbandry can protect sheep from flystrike without surgery (i.e. regular surveillance, crutching, insecticides etc). Unfortunately, given the large numbers run over extensive areas in Australia, and with very low labour levels, sheep do not receive this sort of care and attention.” [1]

 

References:

1 https://www.animalsaustralia.org/issues/mulesing.php

2 https://www.vff.org.au/vff/Documents/Factsheet_Livestock_Flystrike.pdf

3 https://www.vff.org.au/vff/Documents/Factsheet_Livestock_Flystrike.pdf

4 https://www.wool.com/globalassets/start/on-farm-research-and-development/sheep-health-welfare-and-productivity/sheep-health/breech-flystrike/latest-publications/gd2428-2017-managing-flystrike-manual_8_web.pdf