July 8, 2026, 9:33 am | Read time: 8 minutes
Rhythmic sheath noises unsettle many horse owners. Often, respiratory issues or pain are suspected—but usually, something entirely different is behind it. PETBOOK consulted Dr. Olivier Brandenberger, Dipl. ECVS, a specialist in equine surgery and chief veterinarian at the Hanseklinik für Pferde. He explains how the noises occur, when they are harmless, and in which cases a veterinarian should examine the horse.
What Exactly Are Sheath Noises in Horses?
“Sheath noises are described as a rhythmic, sucking, hollow, sometimes smacking sound that geldings and stallions make under exertion—especially at the trot, less often at the gallop,” explains Dr. Brandenberger, chief veterinarian at the Hanseklinik für Pferde. Additionally, it is characteristic that the noise occurs in sync with the movement, the equine surgeon further explains. According to Dr. Olivier Brandenberger, this regular rhythm often leads to misunderstandings.
“Precisely because it is so rhythmic, some owners confuse it with a respiratory noise. As a specialist in respiratory diseases, I am frequently asked about it. “And then part of my job is to distinguish the harmless sheath noise from a real noise from the upper respiratory tract,” explains Dr. Brandenberger.
How Do the Noises Occur?
According to Dr. Brandenberger, the cause is not in the respiratory tract but in the anatomy of male horses. The decisive factor is the air movement in the so-called prepuce, or sheath.
Dr. Brandenberger explains: “The penis is retracted at rest in the so-called prepuce, or sheath.” As soon as the horse moves, the abdominal and back muscles work in sync with the movement, and air is sucked into and pushed out of this skin pouch, the specialist explains. This rhythmic air movement is the actual cause of the noise.
Smegma can also influence how the noise sounds, the expert explains. However, it is not the actual cause. “There is also normal smegma in the sheath—a sebaceous, somewhat sticky secretion. If there is a lot of it and it is thick, it changes the sound: from sucking to more of a smacking—clapping noise. So, smegma is not the actual cause, but it can influence how the noise sounds. Importantly, it is a purely mechanical phenomenon and has nothing to do with the respiratory tract.”
Why Only Male Horses Make These Noises
That only male horses develop these noises has an anatomical background, says Dr. Brandenberger.
“Because only male horses have this sheath with its folded structure and the movable penile pouch. Mares simply lack this anatomy—there is no cavity under the belly where air can move in this way.”
Why Are the Noises Particularly Common at the Trot?
Sheath noises are particularly noticeable at the trot. According to the equine surgeon, the reason lies in the biomechanics of this gait: “The trot is a very even two-beat with a pronounced suspension phase.” Dr. Brandenberger further explains: “This clean, rhythmically consistent, and powerful movement is transmitted through the rhythmic contractions of the abdominal muscles to the abdominal wall, sheath, and penis, pumping the air anew with each step.”
Besides the even movement, the position of the penis in the sheath also plays a role. “The penis is also held in the sheath by its own muscle, which determines its position in the skin pouch and likely influences the sound,” explains Dr. Brandenberger.
Why sheath noises occur less frequently at the gallop, the equine surgeon attributes to the different movement patterns there: “In the gallop, the biomechanical and muscular process is structured quite differently—less rhythmically uniform, which affects the contractions of the abdominal wall muscles and their influence on the sheath and penis. That is probably why.”
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When Do Sheath Noises Occur Most Frequently?
When sheath noises occur most frequently, Dr. Brandenberger explains: “In my experience, you hear them most when horses are relaxed and trotting easily—such as on the longe. And generally, when there is a lot of smegma in the sheath.”
However, the equine surgeon qualifies the suspected connection between the amount of smegma and the volume of the noises: “To be fair, the idea that more smegma leads to louder noises is my clinical observation—this connection has not been systematically scientifically studied, as the whole topic is hardly researched.”
Are Sheath Noises Painful for the Horse?
When asked if sheath noises cause pain, Dr. Brandenberger initially responds with a wink: “You would have to ask the horses—but seriously, I see the phenomenon very often, especially in relaxed horses on the longe.”
From this observation, the equine surgeon derives his assessment: “Relaxation and pain do not go together. I therefore assume that sheath noises are generally painless.”
Should Owners Be Concerned if Their Horse Regularly Makes Sheath Noises?
Dr. Brandenberger has a clear answer to this question: “No. It is a normal phenomenon in geldings and stallions.” For sheath care, the equine surgeon recommends a cautious approach: “In my opinion, it is perfectly sufficient to gently wash the sheath about once a month or as needed with clear water and a soft, damp sponge—provided the horse tolerates it.”
However, Dr. Brandenberger advises against daily cleaning. He explains: “Daily washing is unnatural and rather counterproductive: It irritates the sensitive skin and disrupts the natural balance in the sheath, rather than improving anything.”
When Are Sheath Noises No Longer Harmless?
Although sheath noises are usually harmless, there are exceptions. Dr. Brandenberger explains which warning signs horse owners should take seriously: “If the horse has problems extending the penis, if there is an unpleasant smell from the sheath, or if there are difficulties urinating.”
In these cases, the equine surgeon recommends having the animal examined by a veterinarian: “These are the warning signs that go beyond a harmless noise.”
Can Sheath Noises Be Prevented?
Whether sheath noises can be avoided or at least reduced, Dr. Brandenberger answers: “Basically, you don’t have to do anything. Occasional, gentle sheath cleaning can change the noise a bit or make it quieter because there is less thick smegma.”
However, the crucial point is that the actual cause of the noises remains. Therefore, the equine surgeon explains: “Bu—–and this is important—often washing does nothing because a large part of the noise comes from the air movement, and that simply cannot be washed away.”
Therefore, sheath cleaning primarily serves another purpose: “The cleaning is about comfort and hygiene, not about eliminating the noise.”
A Chance Discovery May Have Saved a Gelding’s Life
When asked about a particularly impressive case from his practice, Dr. Brandenberger recalls an older gelding: “Yes. An older gelding was presented to me because of sheath noises—the owner just wanted to make sure everything was okay.”
During the examination, however, Dr. Brandenberger noticed a noticeable change at the tip of the penis: “During the examination of the sheath, I noticed a fine change on the penis: a flat, reddish shimmering, almost floral pattern in the delicate skin of the penis tip—not yet a real, raised mass, but just a pattern on the surface. Typically, it looked almost as if someone had stamped a pattern on the fine penile skin with red paint.”
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As it turned out, it was an early squamous cell carcinoma: “It turned out to be an early squamous cell carcinoma, a malignant skin tumor. We were able to remove it at a very early stage. It was a lucky coincidence—and a good example of how something important can sometimes be revealed during the opportunity of a seemingly harmless question.”
From this case, Dr. Brandenberger also derives advice for horse owners: “Especially older geldings and horses with unpigmented, light skin on the penis have a certain risk for such tumors. Therefore, it is worth taking an occasional, calm look at the penis and sheath anyway—in an early stage, the chances of healing are best.”
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These Misconceptions About Sheath Noises Persist
Dr. Brandenberger explains which misunderstandings he encounters most frequently: “The most persistent is the notion that the noise is related to testosterone or the ‘masculinity’ of the horse—that is simply wrong. Castrated geldings make it just like stallions; it is solely about anatomy, not hormones.”
The equine surgeon also dismisses the assumption that sheath noises are an indication of back problems: “And in equestrian sports, the interpretation persists that the noise is a sign of back tension. In my experience, it is primarily one thing: a normal, mechanical side noise that means nothing serious.”
The Expert’s Advice to Horse
In conclusion, Dr. Brandenberger summarizes what is important in dealing with sheath noises:
“Stay calm. Sheath noises are simply part of life for many geldings and stallions. In sheath care, less is often more. And if you occasionally clean the sheath anyway, take the opportunity for a quick, checking glance—not out of concern, but as a simple precaution.”