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Accurate application of blowfly treatment essential for closed flock

Didling Farms, based in West Sussex, runs a closed flock, lambing between 900 and 1000 ewes each year. With no expansion currently planned, the farm has worked hard towards ensuring every aspect of their operation follows best practice for optimum productivity. Key to this is utilising correct and thorough application of parasite prevention, and only when needed.

Matt Blyth, Flock Manager at Didling Farms, has experienced loss of production from incorrect application, even if, as he is, thoroughly practised in proper usage of a product. “The few breakdowns I get are due to bad application,” says Mr Blyth. “It’s not the product degrading. It’s always a separate element.”

Didling Farms is a closed flock of 180ha, with 50% utilised as permanent pasture. They use a Lleyn-based flock, crossed with Aberfield rams, to breed replacement ewe lambs. Each year, Didling Farms retains anywhere between 200-500 ewe lambs. With such a large flock, Mr Blyth depends on his attention to detail along with reliable, high performing animal health products to ensure productivity remains high.

Growing need for longer coverage

Speaking about the threat posed by blowfly strike, Mr Blyth highlights the changes in recent years, and the need to adjust application timings as a result.

“When I started at Didling, blowfly would strike in early May around the time we started shearing, but now it’s mid-April, so it’s getting earlier,” says Mr Blyth. “Our earliest recorded instance was 20th March. The season’s getting later as well, going all the way through to mid-October on occasion, much later than it was twenty years ago.”

Mr Blyth also embraces the cost of prevention, over risking treatment and curing after strike. “Prevention is absolutely the best strategy. Every sheep struck loses four to five days of grazing production,” he says. “Also, I’ve noticed an effect on ovulation. If ewes get struck in late September and are put to the ram in November, I can usually guarantee a high percentage of them will be singles. It’s only observation but it has been consistent.”

Mr Blyth uses a programme that includes CLiK EXTRA®, CLiK®, and Crovect® depending on withhold and protection requirements. For CLiK and CLiK EXTRA he is careful to correctly calibrate the pour-on gun and dose as per the correct application method. “We treat depending on what we think the risk elements are. For application with an IGR (Insect Growth Regulator – stop the larvae fully developing and so prevent strike), I use the four stroke technique, and use a new gun every year. The treatment spreads around the whole sheep, but if you haven’t applied the product properly, at some point they’ll be exposed to potential strike.”

“We know the product spreads downwards, so we need to ensure the correct dosage is delivered across the shoulders and back. 90% of the time when I have problems, it’s on the shoulders. When applying, I tended to come down the spine at a slight angle; I realised this was usually on the left shoulder, due to me being right-handed. It’s a small thing, and easily adjusted, but goes to show how even a small error like that can potentially lead to strike.”

Potential economic effect of blowfly strike

On average, struck lambs result in a £10 productivity loss per lamb, compared to preventative treatment of 50p per animal.¹ The economic blow caused by strike is clear, but Mr Blyth emphasises that it goes beyond a simple cost/risk analysis.

“If you’re catching sheep with strike, you use twice as much product to treat that animal. That’s not taking into account the average time of twenty minutes to catch a struck sheep in a group. Labour costs might not be as tangible, but they really add up when you have to catch, treat, and release a struck sheep, even if everything goes as smoothly as it possibly can. Chasing sheep about also increases stress for the whole group, not just the struck animal. It is recognised that stressing sheep in the field or through a race can impact the animal’s daily live weight gain for a short period of time. It’s much more cost-effective to use preventative treatment.”

Advice for treatment

Beyond the application method, treatment at Didling Farms also puts other measures in place to ensure effective protection. “Make sure you have your sheep out of the race or a clamp to ensure you can get round the sheep to apply the product correctly,” says Mr Blyth. “Put them in a large pen with space for between ten and twenty animals, so you have room and they can move around – otherwise the sheep may jump over one another, rubbing off the product you’ve applied and compromising blowfly protection.”

Top Tips for accurate application
  • Ensure the product is applied evenly – be aware of areas you might easily overlook or not cover fully
  • Apply in a spacious area – a pen offers more manoeuvrability than a race
  • Calibrate and recalibrate the gun as you go to ensure correct dosage relative to the accurate weight of the animal
  • Follow the recommended application method for comprehensive coverage
  • Use a product that works for your requirements


“Make sure you apply the product in a way that fully protects your flock and enables a strong daily live weight gain (DLWG) without fear of loss productivity. Lambs that are not properly treated and get struck will fall short in body condition scoring and performance. The knock-on effects are real – take the time and make sure you do the job properly, so you get the best coverage possible and don’t lose protection due to simple oversight.
Matt Blyth Testimonial-1

Matt Blyth Flock Testimonial-1

Matt Blyth Flock 2 Testimonial-1


¹Richard Wall and Fiona Lovatt (2015). Blowfly strike: biology, epidemiology and control, In Practice 37:181-188 doi:10.1136/inp.h1434.
CLiK® contains 5% dicyclanil. CLiK® EXTRA contains 65mg/ml dicyclanil. Crovect® Pour On for sheep contains 1.25 (w/v) cypermethrin (cis:trans/80:20). POM-VPS in UK Information regarding the side effects, precautions, warnings and contra-indications can be found in product packaging and leaflets; further information can also be found in the Summary of Product Characteristics. Advice should be sought from the medicine prescriber. CLiK, CLiK EXTRA , Crovect, Elanco and The Diagonal Bar are trademarks of Elanco or its affiliates. Use medicines responsibly (http://www.noah.co.uk/responsible).