What Is Mulesing and Why Is It Done in Sheep Farming?

Mulesing is a surgical procedure performed almost exclusively on Merino sheep in Australia, in which crescents of woolly skin are cut from the breech area around the tail and buttocks. The resulting scar tissue grows back bare and smooth, making it far harder for blowflies to lay eggs in the warm, moist folds of skin that Merinos are bred to have. The practice has been standard in Australian wool production since the 1930s, and it remains the most widely used method of preventing breech flystrike, a parasitic condition in which blowfly larvae burrow into living flesh and can kill a sheep within days. But mulesing is also one of the most contested animal husbandry practices in the world, with strong research evidence that it causes significant pain and a growing push from retailers, regulators, and advocacy groups to phase it out.

Why Merinos Are Vulnerable to Flystrike

The Australian sheep blowfly, Lucilia cuprina, lays its eggs on skin that is warm, damp, and soiled with urine or feces. Merino sheep are particularly susceptible because decades of breeding for maximum wool yield gave them deeply wrinkled skin, especially around the breech. Those wrinkles trap moisture, and the dense wool covering them creates a microenvironment that blowflies find irresistible. Once eggs hatch, the larvae feed on skin and underlying tissue, causing a condition called “strike.” A struck sheep can go from healthy to fatally ill in two to three days if the infestation is not caught early.

Flystrike is not a marginal problem. Across Australian sheep-grazing regions, it is one of the leading causes of death and production loss in Merino flocks. Mulesing was developed by J.H.W. Mules in the 1930s specifically to address this vulnerability, and the logic is straightforward: remove the skin that traps moisture and you remove the site where flies lay eggs. The procedure is typically performed on lambs between two and twelve weeks of age, often at the same time as tail docking and ear marking.

What the Procedure Does to the Animal

During mulesing, a lamb is restrained on its back and hand-held shears or a specialized knife are used to cut away strips of skin from each side of the breech and around the tail. No general anesthesia is used in conventional mulesing. The open wounds heal over the following weeks, producing long linear scars on either side of the breech and tail, typically within 32 to 47 days.¹ That scarred skin is wool-free and taut, which means it stays dry and unappealing to blowflies for the rest of the animal’s life.

The wound itself is substantial. Until the scar tissue forms, lambs are walking around with open surgical wounds in an area regularly exposed to urine, feces, and environmental contamination. The healing period is the window when the animal is most affected, and the research on what happens during that window is unambiguous about the level of pain involved.

Evidence of Pain and Distress

Multiple studies have measured both the physiological and behavioral responses of lambs to mulesing, and the picture is consistent: the procedure causes acute, significant pain that lasts for days and may persist at lower levels for weeks.

On the hormonal side, mulesed lambs show marked spikes in cortisol and beta-endorphin, the body’s primary stress and pain-signaling hormones, within five to fifteen minutes of the procedure.² Those levels remain elevated through at least 24 hours of post-operative handling, though by 48 hours the hormonal response to routine handling appears to return closer to baseline. Other studies confirm the cortisol surge and also detect rises in haptoglobin, an inflammatory marker that indicates ongoing tissue damage and immune activation.³

The behavioral evidence is equally clear. Mulesed lambs adopt what researchers call “statue standing,” a posture in which the lamb stands motionless with its head lowered and back arched, apparently trying to minimize any movement of the damaged tissue. They make repeated unsuccessful attempts to lie down, walk stiffly, and spend significantly more time standing and less time lying compared with unmulesed control lambs for up to three days. Some behavioral inhibition, including reduced feeding, persists for roughly two weeks. In one study, gait was still measurably poorer than controls at 18 days after treatment.⁴ Mulesed lambs compared with sham-mulesed animals (restrained but not cut) showed large cortisol increases and significantly more hunched standing, confirming that the pain response is from the cutting itself, not just the handling.⁵

Pain Relief During and After Mulesing

Because the evidence for pain is so strong, a major line of research has focused on whether analgesics and anesthetics can reduce suffering when mulesing is performed. The short answer is that pain relief helps considerably in the first hours, though no current product eliminates all discomfort through the full healing period.

Topical anesthetic formulations applied directly to the wound have shown the most dramatic immediate effect. One widely studied product delivers rapid analgesia within about a minute of application, with wound pain significantly reduced for up to 24 hours. Tests of wound sensitivity show that both the primary pain at the wound site and the secondary hyperalgesia in surrounding tissue are absent or markedly diminished in treated lambs. Treated lambs also showed improved wound healing compared with untreated ones.⁶ Follow-up trials confirmed that the analgesic window extends to around 24 hours, with consistently lower pain-response scores in treated lambs.⁷

Topical anesthesia alone, however, does not cover the full duration of pain. Researchers have found that combining a topical anesthetic with a systemic anti-inflammatory drug produces better outcomes than either alone. Lambs receiving both a topical product and an oral or injected anti-inflammatory showed significantly less pain-related behavior on the day of mulesing compared with lambs that received no pain relief.⁸ A pen study evaluating a combination of buccal (cheek-absorbed) meloxicam and topical anesthesia found that cortisol concentrations were lower at 30 minutes post-procedure, and wound-related indicators were not significantly different from sham-mulesed lambs at six and 24 hours.⁹ The consensus from this body of work is that greater analgesic coverage requires pairing topical anesthesia with a non-steroidal anti-inflammatory drug.¹⁰

Even multimodal pain relief, though, has limits. The behavioral evidence shows effects persisting for up to two weeks, well beyond the 24-hour window of topical anesthesia or the day or two of systemic anti-inflammatory action. Current pain relief protocols improve welfare substantially in the acute period but do not make mulesing painless across the entire healing timeline. This gap is one reason the push for alternatives has not eased even as pain-relief uptake has climbed.

How Widely Pain Relief Is Used

Industry surveys suggest that pain relief uptake among Australian producers who mules has increased sharply in recent years. In the state of Victoria, where pain relief during mulesing became mandatory, a 2021 survey of 264 producers found that all of them used some form of pain relief, up from about 85 percent in 2017. In New South Wales, which considered but did not pass a mandate, the rate rose from 88 percent in 2017 to 93 percent in 2021.¹¹ The most common approach is a topical anesthetic spray, sometimes combined with an analgesic injection or oral gel. These numbers reflect self-reported practices, so the real-world consistency of application on every lamb in every flock is hard to verify, but the direction of the trend is clear.

Legislative frameworks vary across Australian states. Victoria has been the most prescriptive, while other states have relied more on codes of practice and industry self-regulation. A parliamentary inquiry in New South Wales in 2019 examined the question of mandating pain relief but did not result in new legislation. The patchwork of rules means that what a lamb experiences during mulesing still depends partly on where in Australia it is raised.

Alternatives That Avoid Surgery

The search for alternatives to mulesing has produced several options, though none yet matches the combination of effectiveness, simplicity, and permanence that mulesing offers. Each involves trade-offs.

Breech Clips

Plastic occlusive clips are applied to the skin folds around the breech, cutting off blood supply so the tissue dies and eventually sloughs off, leaving a result similar to mulesing but without a knife. Clips need to stay on for at least four to six days to produce the desired bare area.¹² In multisite randomized trials, clip-treated lambs showed roughly 16 to 21 percent greater horizontal bare area measurements and about a third higher bare area scores compared with untreated controls, along with lower wrinkle and dag (fecal soiling) scores. The trade-off was a slight reduction in body weight, about 1 to 2 percent, in treated lambs.¹³

On the welfare question, behavioral research indicates that clips cause less distress than surgical mulesing, though they are not pain-free. The tissue necrosis is slower than a surgical wound, and the behavioral disruption appears lower in magnitude.¹⁴ Clips have not achieved wide commercial adoption, partly because producers are uncertain about their long-term efficacy compared with mulesing and partly because the process of applying them can be fiddly under farm conditions.

Chemical and Insecticide-Based Management

Rather than modifying the sheep’s anatomy, another approach is to protect vulnerable sheep through carefully timed chemical treatments combined with management practices like crutching (shearing the wool around the breech) and strategic shearing schedules. Research has shown that in most environments, it should be possible to protect unmulesed sheep against breech strike with an integrated control program incorporating strategically timed crutching, shearing, and application of insect growth regulators such as dicyclanil. Delaying the chemical treatment to at least six weeks after shearing or crutching increased the length of protection compared with treating immediately after shearing.¹⁵

The catch is cost. Economic modeling has estimated that the additional flystrike-related costs for unmulesed flocks range from roughly $220 to $840 per thousand sheep per year, depending on the region and the class of sheep, with hoggets (young sheep) costing more to protect than ewes. The models also indicated that the more potent chemical dicyclanil, rather than the older cyromazine, may be needed to keep flystrike at acceptable levels in unmulesed flocks.¹⁶ For producers operating on thin margins, that added cost is a real barrier, though it needs to be weighed against the growing market premiums some buyers offer for non-mulesed wool.

Genetic Selection

The most permanent solution may be breeding sheep that are naturally resistant to flystrike. The traits that matter are low breech wrinkle scores, low breech wool cover, and low dags. All of these are heritable, meaning producers can select for them. Research has confirmed that genetic correlations exist between wrinkle scores and some wool production traits, and that while a few of those correlations are unfavorable (selecting for fewer wrinkles can slightly reduce wool quantity or change certain quality measures), the trade-offs are manageable when wrinkle scores are included as an additional criterion in standard Merino selection indexes.¹⁷ Modeling work has shown that substantial genetic gains in reducing breech flystrike susceptibility are achievable through index selection that balances productivity traits with flystrike-risk traits.¹⁸

Genetic change is slow. It takes multiple generations to shift a flock’s average wrinkle and breech cover scores far enough that mulesing becomes unnecessary. Some progressive studs in Australia are already producing plain-bodied Merinos that do not need mulesing, but the national flock still contains many animals with high wrinkle and breech cover. Breeding is widely seen as the most sustainable long-term answer, but producers in the middle of the transition still face a gap where their sheep are less wrinkled than their grandparents but not yet low-risk enough to go without some form of flystrike prevention.

Vaccines and Biological Control

A vaccine against the blowfly itself would, in theory, be the cleanest solution: no surgery, no chemicals, no reliance on breeding. Early experimental work showed that partially purified larval antigens could be used to vaccinate sheep, resulting in significantly fewer strikes on vaccinated sheep compared with controls, and surviving larvae that were up to 85 percent smaller than those on unvaccinated animals.¹⁹ That proof of concept was promising, but the protection was partial. A comprehensive review of blowfly control in Australia and New Zealand noted that experimental vaccines have been developed but still require further analysis of antigens and formulations to achieve reliable, commercially viable levels of protection.²⁰ As of now, no blowfly vaccine is commercially available. The gap between “works in a trial” and “works reliably across millions of sheep in diverse environments” has proven stubborn to close.

How Climate Change Complicates the Picture

All of the strategies above, whether surgical, chemical, genetic, or immunological, operate within a climate context that is shifting in a direction that favors the blowfly. Modeling work has shown that the range of temperature increases predicted by current climate change scenarios would elongate the blowfly season, produce earlier spring emergence, and increase the cumulative incidence of strike. The effect is not uniform across sheep classes: a three-degree Celsius rise in average temperature roughly doubles the cumulative strike incidence in lambs but results in roughly four times more strikes in ewes.²¹

That asymmetric impact matters for breeding programs. If ewes face a disproportionate increase in strike risk, genetic selection for low wrinkle and breech cover becomes more urgent in the breeding flock itself, not just in lambs destined for slaughter. A warmer, wetter climate also means chemical-based integrated pest management programs will need to be applied more frequently or at different timings, raising costs further for producers trying to manage unmulesed flocks. The irony is that the very conditions making mulesing more ethically controversial are also the conditions making flystrike harder to control without it.

Market and Supply-Chain Pressure

While the scientific and regulatory debates play out, market forces have become a powerful driver of change. Beginning in the mid-2000s, animal welfare campaigns led by advocacy organizations targeted major international clothing brands, pressuring them to commit to sourcing non-mulesed or pain-relief-mulesed wool. Research examining the dynamics of these campaigns found that they led to significant changes in the rules governing global Merino wool production, though the outcomes were complex. In some cases, corporate actors co-opted the framing of activist campaigns, adopting welfare language and traceability schemes without necessarily requiring the full elimination of mulesing across their supply chains.²²

The practical result is a tiered market. Some brands now accept only wool certified as non-mulesed. Others accept wool from mulesed sheep provided pain relief was used. Still others have no explicit policy. For producers, this creates financial incentives to move away from mulesing or at minimum adopt pain relief, but also confusion about which certification schemes carry real market value. The Responsible Wool Standard, the National Wool Declaration in Australia, and various brand-specific auditing systems all define the terms differently. A grower trying to position their clip for premium buyers needs to navigate a thicket of overlapping and sometimes contradictory standards.

New Zealand effectively banned mulesing in 2018 through an amendment to its animal welfare regulations, though the practice had already been rare there because New Zealand sheep breeds tend to have less wrinkled skin than Australian Merinos. In Australia, where Merinos dominate and flystrike risk is higher, a complete ban has been politically difficult. The Australian Wool Innovation body, which is funded by a levy on wool growers, has invested in developing alternatives while stopping short of calling for a legislated end to the practice. For now, the trajectory is toward mandatory pain relief as a near-term minimum and genetic selection as the long-term replacement, with the timeline depending as much on wool prices and climate as on regulation.