Take steps to act against Blowfly now
Shearing can help to reduce the risk of Blowfly as the fleece provides an ideal incubation ground for the fly to lay her eggs.
We are entering a high-risk period for blowfly strikes, with a number of cases appearing on farms.
The level of burden experienced within a flock is influenced by both the prevailing weather and on-farm conditions. It can pose a significant challenge when correct prevention measures are not in place, strike will typically occur on soiled areas of the fleece first, as the flies are attracted to these areas.
Blowflies are attracted to organic matter or discharge. Soiled, dirty fleeces from animals with scour, footrot or open wounds that may occur from shearing or rams fighting to increase the risk. They are also highly attracted to sheep where strike has already occurred. In damp, humid conditions, this risk is heightened.
The aim should always be to prevent blowfly strike from happening in the first place. There are a number of different options that are available to farmers in this regard.
The efficacy of this method is dependent on the correct dipping procedure, ensuring the dip is made up to the correct strength and replenished periodically, following the manufacturer’s instructions at specified intervals.
Sheep should remain in the solution for a minimum of 60 seconds. The duration of immersion in the dip solution is strongly correlated to the length of time that protection will last for.
This is the most common method used on farm. Several products are available, offering periods of cover from seven to 19 weeks. The correct application method will impact the efficacy.
The meat withdrawal dates vary from seven to 40 days for these products, so care needs to be taken to ensure they are suitable for the farming system. Given the fact that blowfly season is quite long, a repeat application may be required in many cases once the period of cover nears its specified duration.
These common products used can be split into two categories based on their active ingredient and mode of action:
There are a number of pyrethroid-based pour-ons (e.g. cypermetrin – Ectofly, Vector, etc.) which offer short-term cover (six to eight weeks) from flystrike on the areas where they are applied. These products will also kill maggots if they are applied directly to the larvae.
Dicyclanil-based products (e.g. Cliczin, Clik, Clik extra) work by interrupting the life cycle of the larvae. They prevent the stage one larvae, that don’t cause harm, from developing into stage two larvae that have mouthpieces and can cause damage.
These products won’t kill stage two or three larvae (maggots) and, therefore, must be applied before the blowfly lays eggs. There are a number of different products within this category on the market with varying lengths of cover from eight weeks up to 19 weeks.
The fleece provides an ideal incubation ground for the fly to lay her eggs, and shearing will remove this. However, this protection is only short-lived, and strike can occur within weeks during high-risk periods.
As a result, one of the methods outlined above will need to be incorporated into the control programme for these animals.
Key points to remember for treatment:
- Have the control method in place before strike occurs;
- Use products correctly in accordance with manufacturer’s instructions;
- Be aware of the periods of cover provided by each product and the withdrawal dates when selecting stock for sale.
- Put a plan in place to deal with blowfly strike this season, contact your advisor or veterinary surgeon to discuss this further.
