Cryptorchid Testicle Descent in Horses: Can Hormone Therapy Work and Should You Breed?

By Dr Duncan Houston

An undescended testicle in a colt is not just a developmental detail. It changes how that horse should be managed, treated, and in many cases, whether it should be bred at all.

One of the biggest misconceptions is that all cryptorchid cases are the same. They are not.

The location of the retained testicle determines everything. Diagnosis, treatment options, and long-term decisions all hinge on that one factor.

Quick Answer

Hormonal therapy may help some colts with testicles retained in the inguinal canal descend into the scrotum, but it does not work for abdominal cryptorchidism. If the testicle is in the abdomen, surgery is required. Even when descent is achieved, cryptorchidism is often considered heritable, so breeding decisions should be made cautiously.

What Is Cryptorchidism in Horses?

Cryptorchidism occurs when one or both testicles fail to descend into the scrotum.

They may be retained:

• in the inguinal canal just above the scrotum

• within the abdomen

Normal descent occurs late in gestation or shortly after birth. If this process fails, the horse is classified as a cryptorchid, commonly referred to as a rig.

Key principle:

If the testicle is not in the scrotum, it is not functioning normally in terms of temperature regulation, but it can still produce hormones.

Why Location Changes Everything

This is the most important clinical distinction.

Inguinal Retention

• testicle is close to the scrotum

• may still have the potential to descend

• hormone therapy may be considered

Abdominal Retention

• testicle is deep within the abdomen

• will not descend naturally or with hormones

• requires surgical removal

Clinical insight:

If the testicle is abdominal, hormonal therapy is not a treatment. It is a delay.

How Cryptorchidism Is Diagnosed Properly

Early and accurate diagnosis prevents unnecessary treatment and poor decisions.

Physical Examination

• absence of one or both testicles in the scrotum

• sometimes palpable in the inguinal region

Hormonal Testing

• Anti-Müllerian Hormone testing is the most reliable indicator of testicular tissue

• testosterone-based testing may be used in specific cases

Imaging

• ultrasound to locate inguinal or abdominal testicles

• used to guide treatment planning

Practical takeaway:

Diagnosis is not just confirming presence.
It is determining location.

Can Hormonal Therapy Actually Work?

Hormonal therapy is only relevant in a narrow group of cases.

When it may work:

• testicle is located in the inguinal canal

• colt is young

• descent pathway is still functional

Common protocols include:

• hCG to mimic luteinizing hormone

• GnRH to stimulate natural hormone release

What happens biologically:

• increased testosterone production

• stimulation of structures involved in descent

Real-world outcome:

Success rates are variable. Some studies report moderate success, but results are inconsistent across populations.

Clinical reality:

Even when it works, it does not change the underlying developmental issue.

When Hormonal Therapy Should Not Be Used

Hormonal therapy is not appropriate when:

• the testicle is abdominal

• the horse is older with long-standing retention

• location has not been confirmed

Critical mistake:

Using hormone therapy without confirming location.

This leads to:

• wasted time

• delayed surgery

• prolonged behavioural issues

When Surgery Is Required

If the testicle is abdominal, surgery is the only correct treatment.

Surgical options:

• laparoscopic removal

• inguinal exploration depending on position

Requirements:

• proper surgical facilities

• controlled anesthesia

• experienced veterinary team

Clinical insight:

Delaying surgery in these cases does not improve outcome. It prolongs risk.

Severity Framework: How to Approach These Cases

Low Concern

• young colt

• inguinal testicle confirmed

Action:
Consider hormonal therapy with clear expectations

Moderate Concern

• uncertain location

• delayed descent

Action:
Confirm with imaging and hormonal testing before treatment

High Concern

• abdominal retention confirmed

• persistent stallion behaviour

Action:
Plan surgical removal

Critical Situation

• unclear castration history

• behavioural or reproductive risk

Action:
Immediate diagnostic clarification and management planning

Should Cryptorchid Horses Be Bred?

This is where clinical reasoning matters more than opinion.

What is known:

• cryptorchidism is widely considered heritable

• exact genetic mechanism is not fully defined

• recurrence risk within bloodlines is documented

What this means practically:

If a horse required hormonal or surgical intervention to achieve normal testicular position, there is a risk of passing this trait on.

Veterinary perspective:

Breeding cryptorchid horses is generally discouraged.

Not because it is impossible, but because it propagates a preventable issue.

What Should You Do Next?

If you are managing a colt with an undescended testicle:

Step 1: Confirm presence and location

Do not guess

Step 2: Decide based on anatomy

• inguinal may allow hormonal trial

• abdominal requires surgery

Step 3: Set clear expectations

Hormonal therapy is not guaranteed

Step 4: Plan long-term

Include behaviour, management, and breeding considerations

Time checkpoint:

If no descent occurs after a defined treatment period, move forward with surgical planning

Common Mistakes Owners Make

• assuming all retained testicles will descend eventually

• attempting hormone therapy without confirming location

• delaying surgical intervention unnecessarily

• breeding without considering heritability

• underestimating behavioural impact

The most common issue is not the condition itself.
It is delayed or incorrect decision-making.

Prevention and Early Management

Good management starts early.

• check both testicles in young colts

• reassess if not descended within expected timeframes

• investigate early rather than waiting months or years

• plan intervention based on evidence, not assumption

Early clarity prevents long-term complications.

Frequently Asked Questions

Can a retained testicle descend later without treatment?

It can in early life, but the likelihood decreases significantly with age.

Does hormone therapy always work?

No. Success is variable and depends heavily on location and age.

Can abdominal testicles ever descend with treatment?

No. These require surgical removal.

Will behaviour change if the testicle descends?

If both testicles are present and functional, stallion behaviour will remain.

Is it safe to breed a previously cryptorchid horse?

It carries risk and is generally discouraged due to suspected heritability.

Final Thoughts

Cryptorchidism is not a single condition. It is a decision point.

The correct path depends on one thing: location.

If you get that right, everything else becomes clear.
If you get it wrong, treatment becomes ineffective and delayed.

Hormonal therapy has a place, but only in specific cases.
Surgery remains the definitive solution for many horses.

The goal is not just descent or removal.
It is making the right decision early.

If you are unsure whether a retained testicle requires hormonal therapy or surgical intervention, ASK A VET™ can help guide diagnosis, treatment planning, and long-term management with clarity.