Treating flystrike in sheep requires fast action: isolate the affected animal, clip the wool around the strike zone, remove as many maggots as possible, and apply a registered insecticide to kill remaining larvae. Left untreated, flystrike carries roughly a 5% mortality rate among affected animals, and even non-fatal cases cause severe pain and tissue damage. The difference between a recoverable strike and a fatal one often comes down to how quickly you intervene.
Recognizing a Strike Early
Flystrike can progress from egg laying to deep tissue damage within 24 to 48 hours in warm, humid conditions. Catching it early makes treatment far more effective. Struck sheep show a distinct behavioral profile: restlessness, reduced grazing time, and abnormal postures. Research comparing struck and non-struck sheep found a nearly four-fold increase in interruptions to normal grazing, including kicking, tail wagging, head shaking, and head turning.
One of the most reliable early signs is a sheep biting or attempting to bite its own rump. In one study, only flystruck sheep performed this behavior, suggesting it’s essentially diagnostic. Struck animals also spend significantly more time standing in abnormal postures and less time eating. If you notice a sheep standing apart from the mob, stamping its feet, or repeatedly turning to nibble at its hindquarters, check it immediately. You may also notice a dark, wet, discolored patch on the wool, a foul smell, or visible maggots on closer inspection.
Step-by-Step Emergency Treatment
Remove the struck sheep from the mob immediately. Leaving it with the flock attracts more blowflies to the area, putting other animals at risk. Then follow this sequence:
- Clip the wool around the entire affected area, exposing both the active strike zone and any surrounding stained or damp fleece. Leave a clean margin of 2 to 3 centimeters beyond the visible damage. If the sheep has long wool, clip even wider to prevent fleece from hanging back over the wound when the animal is standing.
- Remove visible maggots as you clip. Many will fall away once the wool is removed, but check skin folds and wound edges carefully.
- Apply a registered treatment chemical directly to the clipped area, making sure the wound and surrounding skin are thoroughly covered. Follow the product’s label directions for reapplication intervals.
- Dispose of clipped wool safely. Place it in a black plastic bag and leave it in direct sunlight. The heat inside the bag kills maggots and prevents them from developing into the next generation of flies.
Chemical Treatment Options
Several active ingredients are registered for treating active flystrike. Spinosad-based products are available as aerosol sprays, jetting fluids, and dips, and work for both treatment and prevention. Some aerosol formulations include an antiseptic to help prevent secondary infection and a blue dye so you can see where you’ve applied it. Spray directly onto the wound and about 25 millimeters into the surrounding wool until the area is visibly wet.
Ivermectin-based jetting fluids and hand dressings treat active strikes while also providing protection against restrike for up to 12 weeks under low to moderate fly pressure. For prevention rather than active treatment, insect growth regulators like dicyclanil offer the longest protection windows, with some formulations claiming up to 18 to 24 weeks of coverage.
One important consideration: blowfly populations are developing resistance to several chemical classes. Field strains have shown cross-resistance between dicyclanil and imidacloprid, meaning flies resistant to one are often resistant to the other. The mechanism involves the same detoxification pathway in the flies. If you’re seeing protection failures well before the label’s claimed duration, resistance in your local fly population is the likely cause. Rotate between unrelated chemical groups rather than alternating between dicyclanil and imidacloprid, which should be treated as a single group in any rotation strategy.
Pain Relief and Wound Care
Flystrike is extremely painful. Toxins from damaged tissue and ammonia secreted by maggots are absorbed through the wounds into the bloodstream, causing systemic illness. Providing pain relief improves welfare and supports recovery.
Meloxicam, an anti-inflammatory, is available in both injectable and oral formulations for sheep. Research supports a dose of 1.0 mg/kg body weight; studies using a lower dose of 0.5 mg/kg failed to produce a measurable analgesic effect. For topical pain relief on the wound itself, a combination product containing local anesthetic and antiseptic (Tri-Solfen) can be sprayed directly onto exposed tissue. It works on open wounds, providing immediate numbness at the site while also helping to keep the area clean.
For deep or heavily contaminated wounds, monitor closely over the following days. Maggots can penetrate further than they initially appear, and secondary bacterial infection is common once the skin barrier is broken.
Supportive Care During Recovery
Move struck sheep to a separate “hospital” paddock where you can monitor them regularly without exposing the rest of your flock to fly attraction. Provide fresh feed and water, shade or shelter, and ideally the company of at least one or two other sheep to reduce isolation stress. Severely struck animals may be dehydrated and off feed, so easy access to clean water and palatable forage matters.
Check treated wounds daily for the first few days. Reapply treatment chemicals at the intervals specified on the label, as eggs or larvae you missed during the initial cleanup can restart the cycle. If the wound continues to deteriorate, smells worse, or the sheep shows signs of systemic illness (lethargy, not eating, recumbency), the strike may have progressed to a point where veterinary intervention is needed or euthanasia should be considered on welfare grounds.
Preventing Restrike and Future Cases
Once you’ve treated an active case, prevention across the flock becomes the priority. Timing your crutching or shearing just before the major fly-risk period is one of the most effective non-chemical strategies. Crutching before fly season prevents breech strike for approximately 6 weeks by removing the damp, soiled wool that attracts egg-laying flies. If sheep are scouring, crutching becomes even more important, though ongoing scours can reduce both the effectiveness of the crutch and any chemical protection you apply.
Don’t over-crutch when dag levels are low. Research shows no additional reduction in flystrike risk from an oversized crutch compared to a moderate one when dags aren’t the issue.
For chemical prevention, dicyclanil-based backline products offer the longest protection at up to 18 to 24 weeks when applied off-shears or onto any wool length. However, field evidence of resistance has shown protection failures occurring as early as 3 to 4 weeks into what should be an 11 to 24 week protection period. Other options like ivermectin, spinosad, and cypermethrin provide shorter windows of 10 to 14 weeks but may remain effective where resistance to growth regulators has developed. Choosing the right product depends on your local resistance profile, the length of your fly season, and how recently you’ve shorn.