Flystrike in sheep – act now to reduce risk - Elders Rural Services
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Flystrike in sheep – act now to reduce risk

The recent rainfall in most parts of Australia and rising temperatures as we head towards spring mean this season is likely to bring with it a higher risk of flystrike in sheep.

Flystrike causes considerable pain and suffering to the animal and is thought to cost the wool industry $173 million annually.1 Flystruck sheep have increased rectal temperature, show rapid breathing, and suffer weight loss caused by loss of appetite.2 Affected animals may eventually succumb to blood poisoning and die if left untreated.

Action taken now however, can greatly reduce the risk, and when coupled with an approach that exploits a weak point in the natural life cycle of the fly, can significantly reduce it further.

The life cycle of a fly

The Australian sheep blowfly (Lucilia cuprina) initiates more than 90 per cent of all strikes on susceptible sheep3 and is largely dependent on sheep as a breeding ground.

The female blowfly is particularly attracted to sheep with wool stained and wet from urine and faeces, and lays her eggs in the fleece of the sheep. After hatching the larvae (maggots), feed on the flesh of the sheep, and cause chemical damage due to the ammonia they excrete. Eventually they leave the sheep to pupate in the soil.

In the warm conditions of a normal fly season, the blowfly life cycle takes between 18 days to three weeks. Under ideal conditions however it can be as fast as 12 days, with environmental and soil temperatures the main influence of time. As you can see, fly numbers can build up very rapidly.

In the cooler conditions at the end of the fly season, development is inhibited at the prepupae stage and development is not resumed until conditions are again suitable. The increase in soil temperature in spring in south-eastern Australia has been shown to trigger synchronous emergence of the first generation of flies for the new season, regardless of exactly when the larvae were deposited.

Early season treatment

Chemical treatments applied to sheep now, before flies emerge at the start of the season, essentially removes the animal as a resource for the propagation as the first fly generation appear.

As the first generation is typically small, this can have a significant effect in reducing fly numbers and the risk of flystrike for the balance of the season.

This strategy has been demonstrated to work very effectively on commercial sheep farms in different regions, over a number of years with varying seasonal conditions – and clearly reduces the risk of flystrike.

Flies are not capable of moving long distances, so the success of early season treatment can be even further enhanced if all sheep on a farm are treated, if neighbours treat as well and/or if flocks are physically isolated.

Late season treatment

Chemical treatment applied (or still active) on sheep in late summer and autumn, mean the animal is once again removed as a breeding resource for the flies. This inturn reduces the number of flies that can contribute to the fly population – a great preventative measure for the following season.

Treatment options

Optimum fly control will also depend on farm management practices. Integrating early or late season treatment with shearing and crutching of sheep during spring, early summer and autumn will further reduce susceptibility to flystrike and contribute to reducing fly numbers.

Elders offer a range of animal health products. Some of the more popular chemical treatments for flystrike include:

  • Strikelab – its active ingredient is Dicyclanil. Strikelab is less prone to wash out when there is a rainfall event after application, and has a longer protection period of up to 18 to 24 weeks under ideal conditions.
  • Clik Extra – with its active ingredient Dicyclanil, Clik Extra is indicated for the protection of sheep for up to 29 weeks.
  • Cyrolab Liquid – its active ingredient is Cyromazine, and is a product that needs to be diluted.
  • Cyrolab Spray On –Cyromazine is the active ingredient and is in a ready to use form.
  • Iverlab Blowfly and Lice – its active ingredient is Ivermectin. The product needs to be diluted and gives up to 12 weeks protection against fly strike.

Note: Cyromazine in either form is very prone to washing out when there is a rainfall event and has a protection period up to 12 weeks under ideal conditions. If there is a rainfall event and the protection period of Dicyclanil is reduced, it is safe to say that Cyromazine’s efficacy when used under the same conditions would be reduced to a higher degree.

Regardless of what chemical treatment you use, do be conscious of wool withholding periods as described on the label.  In some ways, early and late season treatments for fly prevention provide long-term benefits in the same way that summer drenching can provide long term benefits for worm control. So start now and reduce the risk for seasons ahead.

For advice you can trust about this and other animal health issues consult your local Elders animal health advisor.

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References:
1. Lane et al 2015.
2. Broadmeadow et al 1984
3. NSW Department Primary Industries 2007.
The information contained in this article is given for the purpose of providing general information only, and while Elders has exercised reasonable care, skill and diligence in its preparation, many factors (including environmental and seasonal) can impact its accuracy and currency. Accordingly, the information should not be relied upon under any circumstances and Elders assumes no liability for any loss consequently suffered. If you would like to speak to someone for tailored advice relating to any of the matters referred to in this article, please contact Elders.