Why Is My Gelding Acting Like a Stallion? Proud Cut, Cryptorchidism and Testing

By Dr Duncan Houston

A gelding that squeals at mares, herds other horses, mounts, develops erections or becomes aggressive can quickly make owners wonder whether something was missed during castration.

The usual stable-yard diagnosis is that the horse was “proud cut.” However, stallion-like behaviour does not automatically mean that testicular tissue remains.

In a large retrospective study of 1,202 presumed geldings investigated because of undesirable behaviour, most had testosterone and anti-Müllerian hormone results below the laboratory’s cryptorchid ranges. Retained testicular tissue remains an important possibility, but behaviour alone is a poor diagnostic test. (ScienceDirect)

Quick Answer

A gelding may behave like a stallion because of retained testicular tissue, but many completely castrated horses continue to show sexual, social or aggressive behaviour.

The old idea that part of the epididymis was left behind and continues producing testosterone is incorrect. The epididymis is not a meaningful source of male hormones. The most useful first-line investigation is usually a veterinary examination followed by a blood test measuring anti-Müllerian hormone, commonly called AMH, together with baseline testosterone. An hCG stimulation test and ultrasound may be added when the initial results are unclear. (Beva Online Library)

Stallion-Like Behaviour in Geldings at a Glance

Possible explanation	Typical clues	What confirms it?
Normal or learned gelding behaviour	Occasional flehmen, mounting, squealing or herding, often directed towards particular horses	Normal AMH and testosterone, reliable castration history and no testis identified
Retained testicle	Unknown or incomplete castration history, persistent sexual behaviour, urine marking, mounting or inter-male aggression	AMH and testosterone testing, hCG stimulation where needed, examination and imaging
Recently castrated stallion	Behaviour present during the first days or weeks after surgery	Time, postoperative assessment and confirmation that both testes were removed
Pain or another medical problem	Sudden aggression, irritability during handling, task-specific behaviour or general behavioural deterioration	Full veterinary examination and investigation of the affected body system
Environmental or social trigger	Behaviour occurs only near particular mares, during group changes or around limited resources	Behaviour history, videos and controlled management changes
Medication or hormone exposure	Behaviour changes after anabolic products, reproductive medication or supplements	Medication review and laboratory testing

What Does “Proud Cut” Actually Mean?

“Proud cut” is an old and imprecise term.

Historically, people believed that a gelding behaved like a stallion because part of the epididymis had been left behind during castration. The epididymis is the coiled structure attached to the testicle that stores and transports sperm.

However, the epididymis does not produce clinically important amounts of testosterone. Leaving part of it behind does not turn it into a secret hormonal spare testicle. Research has demonstrated that the epididymis and spermatic cord do not produce enough testosterone to explain persistent stallion-like behaviour. (Beva Online Library)

The real possibilities are:

1. The horse is completely castrated but retains stallion-like behaviour.

2. One testicle was never removed because it was retained in the abdomen or inguinal canal.

3. Actual testicular tissue survived an incomplete surgical procedure.

4. The behaviour has another medical, social or learned cause.

The term “proud cut” does not distinguish between these very different situations. “Suspected retained testicular tissue” is much more useful.

What Counts as Stallion-Like Behaviour?

Behaviours owners commonly report include:

• Flehmen, with the upper lip curled

• Repeated sniffing of urine or manure

• Squealing or vocalising around mares

• Arching the neck and posturing

• Urinating or defecating repeatedly in particular locations

• Herding or guarding mares

• Chasing geldings away from mares

• Mounting with or without pelvic thrusting

• Erection or penile intromission

• Aggression towards other horses

• Biting, striking or challenging handlers

• Becoming difficult to lead or contain when mares are nearby

No single behaviour proves that a testicle is present.

Flehmen, for example, is a chemosensory behaviour used when investigating odours. Stallions perform it when evaluating urine and manure, but it is not necessarily an immediate attempt to mate. (PubMed)

Similarly, occasional mounting can occur during play, social excitement or learned interaction. The concern increases when several behaviours occur together, are intense and persistent, or create a genuine risk to people or other horses.

Can a Completely Castrated Horse Still Act Like a Stallion?

Yes.

An older retrospective study of 140 male horses found that approximately 20% to 30% of geldings castrated before two years of age still displayed some stallion-like sexual behaviour or aggression towards horses. The frequency was not significantly different in horses castrated after sexual maturity. (Science.gov)

More recent laboratory data tell the same general story from another direction. Among presumed geldings submitted for testing because of stallion-like behaviour:

• 80.6% of available testosterone results were below that laboratory’s cryptorchid range

• 77.8% of available AMH results were below its cryptorchid range

• Some samples had disagreement between testosterone and AMH, showing why one hormone should not always be interpreted alone

These were selected referral samples rather than a random population of all geldings, but the finding is still clinically important. Most behavioural complaints in that dataset were not accompanied by clear hormonal evidence of retained testicular tissue. (ScienceDirect)

Why Can a True Gelding Retain Stallion-Like Behaviour?

The Behaviour May Have Been Learned Before Castration

Castration removes the main source of testosterone. It does not erase the horse’s memory or previous social experience.

A stallion that has already learned to court mares, guard a group, mount or threaten rivals may continue performing parts of that sequence after castration. The behaviour may be reinforced if:

• Mares respond to him

• Other horses move away

• Handlers release him when he becomes difficult

• He successfully gains access to a preferred horse

• Mounting or chasing continues without interruption

Once a behaviour repeatedly produces a useful outcome, it may persist even after the original hormonal drive has fallen.

Some Male Social Behaviour Is Not Completely Testosterone-Dependent

Research and long-term clinical observation show that some masculine behaviour continues in horses with no testicular hormonal activity. A true gelding can show flehmen, courtship, mounting and even intromission without having retained testicular tissue. (PubMed)

The Behaviour May Be Trigger-Specific

Some geldings behave normally until they are:

• Turned out with a mare in season

• Separated from a preferred mare

• Placed in a newly formed group

• Stabled beside an intact stallion

• Transported or moved to an unfamiliar property

• Asked to pass closely beside another horse

• Exposed to competition over feed, water or space

This pattern is often more consistent with social arousal and learned behaviour than constant hormonal stimulation.

Pain or Discomfort May Be Contributing

New aggression should not automatically be labelled sexual behaviour.

Pain can make a horse:

• Defensive about touch

• Aggressive during girthing or grooming

• Reluctant to move away from mares

• More reactive during leading

• Intolerant of other horses approaching

• More likely to bite, kick or threaten

Potential causes include musculoskeletal pain, gastric disease, dental pain, hoof pain, skin disease, eye disease, preputial discomfort and urinary problems.

Equine discomfort can be expressed through changes in posture, interaction, facial expression and activity rather than through an obvious limp. Behavioural and physical problems can also coexist, so correcting the pain may need to be combined with retraining. (PubMed)

What Is Cryptorchidism?

Cryptorchidism means that one or both testicles have not descended completely into the scrotum.

The AAEP defines a cryptorchid as an animal that does not have two testicles palpable in their entirety below the external inguinal rings. A retained testicle may be located:

• Inside the abdomen

• Close to the internal inguinal ring

• Within the inguinal canal

• Beneath the skin near the groin

• Occasionally as small, abnormal or degenerated tissue following previous surgery

A retained testicle may produce little or no useful sperm because of its warmer location, but it can continue producing hormones. (AAEP)

Unilateral Cryptorchid

One testicle is retained and the other has descended normally.

If the descended testicle remains, the horse may be fertile and should be managed as a stallion. Both testicles should be removed rather than removing only the visible one and leaving the retained testicle behind. (American College of Veterinary Surgeons)

Hemicastrated Cryptorchid

The descended testicle has already been removed, but the retained testicle remains inside the abdomen or inguinal region.

This horse may be presented or sold as a gelding even though testicular tissue is still producing hormones.

Bilateral Cryptorchid

Both testicles are retained.

These horses are generally sterile because neither testicle is maintained at normal scrotal temperature, but they may still have normal male secondary characteristics and stallion-like behaviour. (MSD Veterinary Manual)

Is Cryptorchidism Hereditary?

The condition is considered heritable or to have a substantial genetic component. Affected horses should not be used for breeding, even when a descended testicle remains functional. Surgical removal of both testicles is recommended. (American College of Veterinary Surgeons)

When Is Retained Testicular Tissue More Likely?

Retained tissue becomes more suspicious when:

• The castration history is unknown

• No operative report is available

• The horse was purchased through a sale or auction as a gelding

• The previous veterinarian documented only one removed testicle

• One testicle was known to be absent from the scrotum before surgery

• The horse was described as a rig, ridgling or cryptorchid when young

• The behaviour is persistent, intense and strongly directed towards mares

• The horse repeatedly mounts with erection or intromission

• There is persistent urine or manure marking

• The horse guards mares and aggressively drives other males away

• The horse has a markedly stallion-like appearance and behaviour despite an uncertain history

• The behaviour began or became obvious after the horse entered a breeding or mixed-sex environment

None of these findings confirms cryptorchidism. They simply justify investigation.

When Is a Behavioural Cause More Likely?

A non-hormonal explanation becomes more likely when:

• Both testicles were clearly documented as removed

• AMH and testosterone results are consistent with a gelding

• The behaviour occurs only around one particular horse

• The horse has displayed the same behaviour for years without progression

• There is no urine marking, guarding or broader reproductive behaviour

• The horse mounts during play but is otherwise manageable

• Aggression is linked to feeding, handling, pain or confinement rather than mares

• The behaviour improves substantially with management changes

• The horse shows no consistent seasonal or reproductive pattern

The distinction matters because abdominal surgery will not cure behaviour caused by learning, pain or social management.

How Do Veterinarians Diagnose a Retained Testicle?

1. Review the Castration History

The most useful document may be the original surgical record.

The veterinarian will look for:

• Whether both testes were palpable before surgery

• Whether both were visually identified and removed

• Whether one testicle was retained

• Which surgical approach was used

• Whether tissue was submitted for histopathology

• Whether the horse was microchipped and the surgery permanently recorded

• Whether there was an unsuccessful previous exploration

The AAEP recommends permanent identification and documentation when a retained testicle is removed while another testicle remains, because incomplete records can lead to unnecessary repeat surgery later. (AAEP)

2. Perform a Physical Examination

The examination may include:

• Palpation of the scrotum

• Palpation of the inguinal regions

• Examination of castration scars

• Assessment of the penis and prepuce

• Rectal palpation in suitable horses

• Evaluation of behaviour and physical development

• A general examination for pain or illness

Not every retained testicle can be felt. A small abdominal testicle may leave no externally detectable evidence.

3. Measure AMH and Testosterone

Current diagnostic practice increasingly uses a combination of:

• Anti-Müllerian hormone

• Baseline testosterone

AMH is produced by Sertoli cells within testicular tissue. Testosterone is produced by Leydig cells.

A high concentration of either hormone may indicate retained testicular tissue. However, the results must be interpreted using the reference range and assay used by the testing laboratory. Generic cut-offs copied from another laboratory may not apply. (vet.cornell.edu)

Comparing the Main Blood Tests

Test	What it measures	Main advantage	Main limitation
AMH	Sertoli-cell activity	Single sample, useful in young horses and often remains detectable in cryptorchid tissue with low testosterone production	Rare very small or severely degenerated remnants may produce little AMH
Baseline testosterone	Leydig-cell hormone production	Widely available and useful when clearly elevated	A cryptorchid testicle may produce a low or borderline result
AMH plus testosterone	Two different testicular cell populations	Stronger first-line assessment than either test alone	Discordant results may still require further testing
hCG stimulation test	Testosterone response after hormonal stimulation	Can clarify equivocal results	Requires timed samples, laboratory-specific protocol and veterinary administration
Estrone sulfate	Conjugated oestrogen associated with testicular activity	Historically useful as a single sample in mature horses	Less useful in young horses and no longer offered for male horses by some laboratories

Cornell currently describes AMH as the most reliable test for detecting testicular tissue and uses an AMH plus testosterone panel as its first-line equine cryptorchid panel. It recommends hCG response testing when the panel is indeterminate or when exogenous steroid exposure is a concern. (vet.cornell.edu)

Why Is AMH So Useful?

AMH is especially useful because:

• It is produced specifically by testicular Sertoli cells in male horses

• It can be measured from a single serum sample

• It is present in young males before testosterone becomes consistently measurable

• Cryptorchid testes may continue producing substantial AMH even when testosterone production is low

• Geldings generally have very low or undetectable concentrations once enough time has passed after castration

Studies have found detectable AMH in intact and hemicastrated cryptorchid horses but not in established geldings. Cryptorchid stallions also tend to have higher AMH concentrations than normal mature stallions. (J-STAGE)

Can an AMH Test Ever Be Falsely Negative?

Rarely.

A case has been reported in which a horse had a very small, severely degenerated abdominal testicle but undetectable AMH and no testosterone response to hCG. The tissue contained very few functioning Sertoli and Leydig cells. (PubMed)

This is uncommon, but it explains why a negative blood test should be reconsidered when the surgical history, examination or imaging remains strongly suspicious.

How Soon After Castration Can AMH Be Tested?

Timing matters when the horse has only recently been castrated.

In one study of four stallions:

• AMH began falling promptly after surgery

• The estimated biological half-life was approximately 2.5 days

• Concentrations fell below 1 ng/mL within approximately 8 to 10 days

• AMH was no longer detected by two weeks after castration

The veterinarian should discuss the timing with the laboratory rather than submitting the sample immediately after surgery and attempting to interpret residual hormone as retained tissue. (PMC)

Is One Baseline Testosterone Result Enough?

Not always.

Testosterone can vary with:

• Age

• Season

• Time of sampling

• The size and location of the retained testicle

• Degeneration within retained tissue

• Recent medication or anabolic steroid exposure

• The laboratory assay used

Cryptorchid testicles may produce less testosterone than normally descended testes. Therefore, a low baseline testosterone result does not reliably rule out retained tissue by itself. (vet.cornell.edu)

A clearly elevated testosterone result is useful. A low or borderline result should usually be interpreted alongside AMH and the rest of the clinical picture.

What Is the hCG Stimulation Test?

Human chorionic gonadotropin, or hCG, stimulates functioning Leydig cells to produce testosterone.

The general process involves:

1. Collecting a baseline blood sample

2. Administering hCG under veterinary supervision

3. Collecting another sample after the laboratory’s specified interval

4. Comparing the testosterone response

A horse with functioning testicular tissue should produce a meaningful testosterone response. A true gelding should not.

Protocols vary between laboratories. Cornell currently uses a two-hour post-hCG sample, while other historical protocols have used later samples. The veterinarian should follow the receiving laboratory’s current instructions rather than using an internet recipe assembled from several decades of research. (vet.cornell.edu)

Is Estrone Sulfate Still Used?

It may still be available through some laboratories, particularly for mature horses.

However, estrone sulfate is less reliable in young horses, and testing availability has changed. Cornell retired its male equine estrone sulfate and testosterone cryptorchid panel in January 2025 and replaced it with AMH plus baseline testosterone. (vet.cornell.edu)

This does not make every previous estrone sulfate result invalid. It means the preferred testing strategy is evolving as AMH testing becomes more widely available.

Can Ultrasound Find a Retained Testicle?

Often, yes.

Depending on the suspected location and the horse, a veterinarian may use:

• External inguinal ultrasound

• Transabdominal ultrasound

• Transrectal ultrasound

In one study of 38 horses, transabdominal ultrasound correctly located retained testes with a sensitivity of 97.6% when two horses with inadequate coat contact were excluded, and 93.2% when all horses were included. Specificity was 100% in that study. (PubMed)

Another study of inguinal ultrasound reported a sensitivity of 98% and specificity of 97% for predicting whether a retained testicle was inguinal rather than abdominal. (Beva Online Library)

These results are encouraging, but real-world accuracy still depends on:

• Operator experience

• Equipment

• The horse’s size and temperament

• Hair coat

• Gas and intestinal position

• The size and degree of degeneration of the tissue

• Previous surgery and scarring

Imaging is particularly useful after blood tests suggest that tissue is present, because knowing its likely location helps the surgeon choose the safest approach.

What Happens if Retained Testicular Tissue Is Confirmed?

Surgical removal is recommended.

The approach depends on where the tissue is located and whether another testicle remains.

Inguinal Surgery

A testicle retained within or close to the inguinal canal may be removed through an inguinal incision.

This approach may require general anaesthesia and careful identification of the spermatic cord, inguinal structures and blood vessels.

Standing Laparoscopy

An abdominal testicle may be removed laparoscopically while the horse is sedated and standing in stocks.

Small flank incisions allow a camera and surgical instruments to enter the abdomen. The surgeon can identify the retained testicle, seal its blood supply and remove it under direct visualisation.

Laparoscopy Under General Anaesthesia

The horse may instead be placed on their back under general anaesthesia. The laparoscope and instruments are introduced through abdominal portals, and the testicle is removed through an enlarged portal or separate incision.

Retrospective case series have reported successful removal and low complication rates using several laparoscopic techniques. In one series of 43 horses, no short-term or long-term complications were reported. Another series successfully removed 90 retained testes from 79 horses, with two minor incision-related complications during hospitalisation. (PubMed)

Surgery is not risk-free. Possible complications include haemorrhage, infection, anaesthetic complications, injury to abdominal structures, swelling and incisional breakdown.

Why Must the Testicular Tissue Actually Be Removed?

Simply cutting or sealing the spermatic cord inside the abdomen and leaving the testicle behind is not completely reliable in every situation.

Research involving 241 horses found that some inguinal and normally descended testes retained viable tissue after intra-abdominal spermatic-cord transection because they had an alternative blood supply. The authors concluded that laparoscopic castration without removal of the testicle could not be considered reliable for inguinal cryptorchids or normal descended testes. (PubMed)

The surgeon should remove the testicular tissue in its entirety whenever possible and confirm what has been removed.

Should Both Testicles Be Removed?

Yes, unless both have already been conclusively removed.

If a cryptorchid horse still has a normally descended testicle, removing only the retained testicle would leave a fertile stallion.

Conversely, removing only the descended testicle and leaving the retained testicle creates the classic hemicastrated cryptorchid that may later be mistakenly represented as a gelding.

Both testicles should be accounted for through:

• Direct surgical identification

• Previous reliable records

• Histopathology where uncertainty remains

• Follow-up endocrine testing when appropriate

Will the Stallion-Like Behaviour Stop After Surgery?

It may improve, but it is not guaranteed to disappear.

Hormonal production falls quickly once all testicular tissue is removed. AMH declines over days, while testosterone falls much faster. However, the horse’s established behaviour, social experience and learned responses do not disappear at the same speed. (PMC)

The horse may require:

• Several weeks for hormonal and environmental arousal to settle

• Separation from mares during the early period

• Consistent handling

• Retraining around triggering situations

• A more suitable turnout group

• Review of any pain or management factors

The ACVS notes that learned stallion behaviours may take time and training to change and can persist indefinitely in some horses, even after complete removal of testicular tissue. (American College of Veterinary Surgeons)

Do not promise an owner that surgery will automatically convert a dangerous horse into a quiet children’s pony. Surgery removes the hormonal tissue. It does not install a new personality overnight.

What if the Hormone Tests Confirm That He Is a True Gelding?

Once retained testicular tissue has been reasonably excluded, the investigation changes direction.

Look for Pain or Medical Disease

A veterinary examination becomes especially important when the behaviour:

• Started suddenly

• Is becoming progressively worse

• Occurs during specific handling or ridden tasks

• Is associated with touching the flank, back, girth or prepuce

• Is accompanied by lameness

• Is associated with difficulty urinating

• Occurs with weight loss, appetite changes or colic

• Is accompanied by visual or neurological changes

Potential investigations may include:

• Lameness and musculoskeletal examination

• Back and saddle assessment

• Dental examination

• Eye and neurological examination

• Preputial and penile examination

• Urinalysis or urinary evaluation

• Gastrointestinal investigation

• Review of medications and supplements

Identify the Exact Trigger

Keep a written or video record showing:

• Which horses are nearby

• Whether a mare is in season

• Where the behaviour occurs

• Whether feed is present

• Whether the horse is being led, ridden or turned out

• What happens immediately before the behaviour

• What consequence follows it

• Whether the behaviour is directed towards horses, humans or both

“Acts like a stallion” is too broad for a useful training plan.

“Herds one particular mare, drives geldings away and threatens the handler when removed from her” gives the veterinarian and behaviour professional something far more specific to work with.

Adjust the Social Environment

Depending on the horse, safer management may involve:

• Turnout with compatible geldings

• Avoiding mares that strongly trigger the behaviour

• Preventing fence-line breeding attempts

• Providing enough space to reduce conflict

• Using multiple feeding and water locations

• Avoiding group arrangements in which the horse guards one mare

• Separating the horse from foals or vulnerable individuals

Complete social isolation is rarely an ideal long-term solution. The aim is compatible social contact without repeated mounting, harassment or injury.

Retrain the Behaviour

A qualified equine behaviour professional or experienced trainer should focus on:

• Clear leading and personal-space responses

• Reinforcing calm attention

• Removing the horse safely before arousal escalates

• Practising around triggers at a manageable distance

• Rewarding alternative behaviour

• Avoiding accidental reinforcement of striking, barging or mounting

• Ensuring handlers are consistent

Punishment may suppress warning signals while increasing fear or conflict. A horse that has learned to drive people away may require structured retraining, not a louder argument involving a lead rope.

How Worried Should You Be?

Risk level	What it looks like	What to do
Lower risk	Occasional flehmen, squealing or mounting, but the horse is manageable and does not injure others	Record the pattern and discuss it at the next veterinary visit
Moderate risk	Persistent herding, guarding mares, repeated mounting or escalating conflict with horses	Arrange veterinary examination and AMH plus testosterone testing
High risk	Unknown castration history, repeated intromission, aggressive urine marking, striking, biting or dangerous behaviour around mares	Manage the horse as a potential stallion until testing is completed
Critical	The horse is attacking people, jumping fences, causing serious injuries, displaying severe abdominal pain or showing sudden neurological abnormalities	Secure the area and obtain urgent veterinary assistance

When Is This an Emergency?

Stallion-like behaviour itself is not always an emergency. The danger it creates may be.

Seek urgent veterinary help when:

• The horse is repeatedly striking, biting or charging people

• The horse is mounting another horse that cannot escape

• A mare, foal or smaller horse is being injured

• The horse is attempting to jump or break through fencing

• There is a deep bite, kick wound or uncontrolled bleeding

• The horse develops sudden severe abdominal pain

• The abdomen appears enlarged or painful

• The horse becomes weak, collapses or is unable to stand

• The behaviour is accompanied by incoordination, seizures or abnormal awareness

• Sudden aggression is accompanied by severe pain, fever or difficulty urinating

Rare cases of torsion and tumours involving retained testicles have been reported in horses. Two cryptorchid stallions developed colic from torsion of retained neoplastic testes, and a malignant Sertoli cell tumour has been reported in a horse presumed to be a gelding. These complications are unusual, but they are reasons not to ignore sudden abdominal pain in a known cryptorchid horse. (PubMed)

What To Do Right Now

1. Do not enter a confined area alone with a dangerously aroused horse.

2. Move mares, foals and vulnerable horses away, rather than attempting to drag the gelding through the group.

3. Use secure stallion-standard fencing until reproductive status is known.

4. Do not punish or challenge the horse at close range. Human safety comes first.

5. Call your veterinarian and explain the behaviour, castration history and immediate risk.

6. Record a video from a safe position if the behaviour is intermittent.

7. Do not administer reproductive hormones, sedatives or leftover medication without veterinary direction.

What Should You Do Next?

1. Find the Records

Ask the previous owner, veterinarian or breeding farm for:

• Castration report

• Date of surgery

• Whether two testicles were removed

• Whether a testicle was retained

• Histopathology results

• Microchip-linked medical records

• Any previous endocrine test results

2. Manage the Horse Conservatively

Until reproductive status is clear:

• Do not turn the horse out with mares

• Do not allow access to breeding animals

• Use secure fencing

• Avoid inexperienced handlers

• Prevent contact with foals

• Treat the horse as potentially fertile if any descended testicle may remain

3. Arrange a Veterinary Examination

The veterinarian can assess the scrotum, inguinal area, surgical scars, general health and behaviour pattern.

4. Submit AMH and Testosterone

A combined test is usually the most efficient first step when history and examination do not give a clear answer.

5. Add an hCG Test if Needed

When results are equivocal or conflicting, the veterinarian and laboratory may recommend an hCG response test.

6. Locate the Tissue

If blood tests support retained tissue, ultrasound can help determine whether it is inguinal or abdominal and guide referral.

7. Remove Confirmed Tissue

Surgery should be performed by a veterinarian experienced in equine cryptorchidectomy, often at a hospital or specialist facility.

8. Reassess the Behaviour

After recovery:

• Record whether the frequency declines

• Continue safe management

• Address learned behaviour

• Investigate pain if aggression persists

• Do not assume the surgery failed simply because the horse still squeals at a mare during the first few weeks

Common Mistakes Owners Make

Assuming Every Riggy Gelding Has a Retained Testicle

Most behaviour-related samples in the large 2024 study were not hormonally consistent with cryptorchidism. Testing is more reliable than stable-yard certainty. (ScienceDirect)

Blaming the Epididymis

The epididymis is not a testosterone factory. Actual testicular tissue must be present for testicular hormonal production.

Relying on One Low Testosterone Result

A retained testicle may produce a low baseline concentration. AMH and, where necessary, hCG stimulation provide a stronger assessment.

Testing Immediately After Castration

Residual AMH can remain measurable for days. Sample timing should be discussed with the laboratory.

Sending the Horse Straight to Abdominal Surgery

History, endocrine testing and ultrasound can reduce unnecessary exploration and help the surgeon plan the correct approach.

Expecting Surgery to Erase Learned Behaviour

Hormones fall faster than habits.

Punishing Dangerous Behaviour

Punishment can escalate aggression, remove warning signals and place the handler in striking or kicking range.

Ignoring Sudden Behavioural Change

A horse that suddenly becomes aggressive may be painful, neurologically abnormal or medically unwell, even if the behaviour looks vaguely masculine.

Can Stallion-Like Behaviour Be Prevented?

Not every case can be prevented, but several problems can be avoided.

Confirm Both Testicles Before Routine Castration

The veterinarian should identify both testicles completely before beginning a routine field castration.

When only one is palpable, the horse should be treated as a cryptorchid rather than removing the visible testicle and hoping the other one appears later.

Document What Was Removed

Records should identify:

• Left and right testicle

• Surgical approach

• Any retained testicle

• Complications

• Histopathology where relevant

• The horse’s permanent identification

Do Not Breed Cryptorchid Horses

Even a unilateral cryptorchid with one fertile descended testicle should not be used for breeding because of the hereditary concern.

Provide Good Handling Education

Castration does not replace training.

Colts and recently castrated horses should still learn:

• Personal-space boundaries

• Calm leading

• Safe turnout behaviour

• Appropriate interaction with people

• How to separate from companions

• How to remain controlled around mares

Address Behaviour Early

Herding, mounting and guarding are easier to manage before they become a repeatedly successful pattern.

Frequently Asked Questions

Can a real gelding still mount and breed a mare?

A gelding can develop an erection, mount and occasionally achieve intromission. A completely castrated horse cannot produce sperm, but the behaviour itself may continue. Because appearance alone cannot confirm reproductive status, a horse with uncertain history should be tested before being allowed near breeding mares.

Does “proud cut” mean part of the epididymis was left behind?

That is the traditional explanation, but it is incorrect. Epididymal tissue does not produce enough testosterone to cause stallion-like behaviour. The concern is retained or surviving testicular tissue.

What is the best blood test for a proud-cut gelding?

AMH combined with baseline testosterone is currently one of the strongest first-line approaches. AMH is generally the most reliable single marker, while hCG stimulation may be added when results are equivocal. (vet.cornell.edu)

Can a cryptorchid horse get a mare pregnant?

A unilateral cryptorchid can be fertile when the normally descended testicle remains. A bilateral abdominal cryptorchid is generally sterile but still hormonally active. Until the anatomy is confirmed, manage the horse as potentially fertile.

Will removing the retained testicle stop the behaviour?

It should remove the source of testicular hormones and may substantially reduce the behaviour. However, learned sexual and aggressive patterns can take weeks to improve or may persist indefinitely. Management and retraining may still be required.

Final Thoughts

A gelding acting like a stallion does not automatically mean that the castration was incomplete.

Retained testicular tissue is important to rule out, particularly when the history is unknown, only one testicle was documented as removed or the horse displays persistent reproductive and aggressive behaviour. The most useful modern pathway is usually:

1. Review the surgical history

2. Examine the horse

3. Test AMH and testosterone

4. Use hCG stimulation when results are unclear

5. Locate confirmed tissue with ultrasound

6. Remove retained testicular tissue surgically

7. Reassess and retrain any behaviour that remains

The term “proud cut” tends to create more confidence than clarity. What matters is whether functioning testicular tissue is actually present.

Once that question has been answered, the horse can receive the correct treatment rather than undergoing abdominal surgery for a behavioural problem or being punished for behaviour driven by a retained testicle.

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ASK A VET™ can help you organise behaviour videos, castration records, hormone results and changes following treatment so that the pattern can be reviewed in context. A horse showing dangerous aggression, severe abdominal pain or sudden neurological behaviour still requires prompt hands-on veterinary care.