With temperatures rising over the last week or so, blowfly strike prevention will be the next task on many farmers’ to-do lists over the coming weeks.

It hasn’t been as much of a problem on many farms so far this year, with this mainly down to the weather – as temperatures have only been on the rise of late.

Blowfly is an external parasite that commonly appears over the summer months, however, it is not uncommon to hear cases as early as April and as late as November.

In late spring coming into the summer months, the population of flies increases rapidly. This, along with the onset of warm, humid weather and rainfall, are the main contributing factors for the onset of flystrike.

Sheep that have a soiled fleece are most at risk of being struck down with flystrike. So dagging/crutching dirty sheep will go a long way in reducing the risk of blowfly strike in the short-term.

The most common area that sheep are affected is around the tail or rump region. However, they can also become infected on the shoulder, along the back or where a cut has occurred on the skin.

Blowfly strike occurs when flies become attracted by a foul-smelling, soiled fleece and deposit many hundreds of eggs onto affected sheep. These eggs will then hatch into larvae and begin to feed on the sheep’s skin – causing wounds.

Within a matter of days, if action is not taken, more and more sheep will become infected.


Obvious symptoms that sheep have been struck down with flystrike include: foot-stamping; vigorous shaking; gnawing or rubbing of the tail; restlessness; wool loss; and loss of body condition.

Early treatment before the population of flies increases substantially will give farmers the best chance of controlling the outbreak of flystrike.

The good news is that farmers have options when it comes to controlling and preventing the outbreak of flystrike.

Shearing ewes at this time will protect them over the coming months – so pour-ons would be the most favoured choice of product by farmers when treating lambs for the parasite.

Choosing a pour-on solution

It’s important to note that there are significant differences with pour-ons, with some only providing protection against certain parasites.

As well as that, some products will treat and prevent against a parasite, while others will only prevent against. So, both of these factors need to be taken into account when purchasing a product.

Pour-ons will provide protection against flystrike for generally up to 10 weeks or so, however, there are some products that provide protection for up to 19 weeks.

It is important to be mindful of the withdrawal periods associated with pour-on products. These can vary from seven days up to 40 days.

For farmers with ewes or lambs coming close to slaughter, it is essential that the withdrawal periods are adhered to.

Finally, care should be taken when using products to treat against flystrike. Protective clothing, gloves and a respiratory mask should be worn.

When treating for flystrike, it is important that farmers keep the following points in mind:
  • Apply in dry weather;
  • Apply to clean, dry wool – crutch excessively dirty sheep;
  • Treat lambs early before flystrike is anticipated;
  • Consider withdrawal periods when selecting a treatment;
  • When using a pour-on product, make sure to apply it from the neck down to the rump area.