Flystrike preventative products: Do you have resistance issues?

AWI estimates that flystrike causes a national annual production loss of around $227 million, and the cost of preventatives and treatments sits at $96 million¹. In the Australian flock, this equates to around $4.76 per head.

With that in mind, it is important that you are getting the most out of your flystrike preventative products.

If you are experiencing flystrike incidents earlier than the expectation set by the product label, several factors should be considered prior to concluding that chemical resistance is the cause.

In this article I have laid out a few factors I would recommend checking, which may help you discern the cause of the issues you are experiencing.

Firstly, take a closer look at the struck individuals to see if they have an extra disadvantage that promotes flystrike susceptibility. Examples include: urine stain, heavy dags, fleece rot, or lumpy wool. Any of these conditions could worsen flystrike for your stock.

If your sheep have moderate or severe dags, could the dags have interfered with effective application of the preventative chemical?

Consider whether this is the first time you have noticed the issue. Have the individuals been struck before? There are a variety of reasons why some individuals are more susceptible to strike than others, such as:

• Animals with any skin lesions, such as skin tears, food abscesses or dog bites
• Lambs and weaners can be more susceptible due to their body conformation, structure and tail length, as they are unclassed

Weather can also have an impact. For example, has there been heavy rainfall directly following the application of the product? Short but frequent showers in particular could interfere significantly with a product’s potency. Consider also that such rainfall could increase fly pressure due to moisture. Warm weather, particularly temperatures between 15 and 26 degrees, combined with a low wind speed, also increases your risk. In temperatures exceeding 38 degrees, flies become largely inactive. There are various predictive tools available that can create a heat map for high risk areas. They assess several key contributing factors, which are largely a combination of humidity, temperature and rain.

Be sure to monitor your stock so that affected individuals could be treated early. Additionally, ensure that treatments and strike dressings have been effective; all maggot trails should be detected so a clean wound border can be achieved.

And finally, sometimes the problem might have a simple solution! Check the label of the applied product to ensure that all instructions were strictly followed, including proper dosage, pattern of application, using fit-for-purpose equipment.

If any of these factors stand out to you, something other than resistance may be reducing the efficacy and protective period of the active chemical.

If you suspect that you are experiencing resistance issues, or the root of the problem is unclear, it is best to speak with an animal health professional to get to the bottom of it. They can help you create a parasite management plan to avoid issues going forward.

This article was written by TEC Livestock Production Consultant, Pip Houghton.

References
1. Australian Wool Innovation, ‘It’s Fly Time!’