One of the most worrying experiences for a breeder is when a proven stud dog suddenly stops producing puppies. He ties normally, his libido seems unchanged — yet every bitch he mates comes back empty.

If you’ve found yourself wondering “why won’t my dog get bitches pregnant anymore?” or searching for answers around male dog infertility, you’re not alone. I support breeders all over the world through my Elite Breeder Formula program, and sudden fertility problems in stud dogs are far more common than most people realise.

The good news: many causes are temporary and fully reversible once identified.

Below, I’ll walk you through the real reasons a healthy, previously fertile male can abruptly go sterile — and what to do next.

1. Heat Stress and Testicular Overheating (The No. 1 Cause)

When it comes to sudden stud dog fertility problems, the testicles’ temperature is everything.
Sperm must be produced 2–4°C [4 to 7°F] cooler than core body temperature. Anything that warms the testicles — even for a short time — can shut down sperm production for 6–10 weeks.

Common heat sources that cause male dog infertility:

• Fever or systemic infection

• Hot weather or heatwaves

• Lying on heated floors, electric blankets, or synthetic bedding

• Long car rides on warm seats

• Excessive licking due to irritation

• Scrotal inflammation from bites, grass seeds, or trauma

• Obesity (fat insulates the testicles)

Heat-damaged sperm die off quickly. Because it takes 62 days to grow a new batch, infertility often appears suddenly — but reflects heat events from weeks earlier.

This is the first thing I investigate in any suddenly sterile stud.

Years ago my stud boy Shadow suddenly failed to get three bitches in a row pregnant.  After some investigation the reason became clear:  being a bit taller and more athletic than my girls, he was able to jump over the fence around the dog yard.  Now and then he gave a little yelp from hitting his testicles on the top of the fence.  Adding a little height to the fence stopped him from jumping over, and within 8 weeks his sperm quality and viability was back to normal :).

2. Prostatitis or Reproductive Tract Infection

Even with a negative Brucella test, prostatitis is extremely common and one of the leading causes of declining semen quality.

Signs can be subtle:

• Cloudy or jelly-like pre-ejaculate

• Dripping from the sheath

• Straining to urinate or defecate

• Strong odour from the penis

• Irritability or restlessness

Prostatitis can cause:

• low sperm count

• poor motility

• abnormal morphology

• complete male dog infertility until treated

The good news? Once the infection is cleared, fertility often returns.

3. Age-Related Fertility Decline

Male dogs don’t stay fertile forever. Many studs start declining at 6–8 years, sometimes earlier depending on breed genetics.

Age-linked changes include:

• lower testosterone

• reduced semen volume

• increased DNA fragmentation

• decreasing litter sizes

• eventual sterility

A stud may still tie enthusiastically while producing sperm that can’t fertilise eggs.

This is a frequent cause of stud dog fertility problems in small breeds [as they have small testicles!].  And in my experience the loss of fertility can happen quite suddenly.

4. Autoimmune Orchitis or Epididymitis

In some dogs, the immune system mistakenly attacks the sperm-producing structures. This can cause sudden male dog infertility, sometimes permanent.

Possible signs:

• painful or shrinking testicle(s)

• mismatched testicle size

• reluctance to be examined

This condition requires rapid veterinary attention to preserve any remaining fertility.

5. Medications and Toxins

Certain drugs can temporarily or permanently affect stud dog fertility:

• systemic corticosteroids

• some antibiotics

• long-term NSAIDs

• chemotherapy agents

• accidental exposure to oestrogen-containing products

• environmental toxins (garden chemicals, moulds, mycotoxins)

Even a short course of the wrong medication can disrupt sperm for a full 1–2 cycles.

6. Hypothyroidism

An often-overlooked cause of male dog infertility is low thyroid function.

It can cause:

• reduced libido

• poor semen quality

• low sperm count

• abnormal sperm morphology

Many infertile studs improve significantly after thyroid correction.

 7. Genetic or Developmental Testicular Degeneration

Some bloodlines carry a predisposition to early testicular degeneration.
These dogs may breed well for a few years, then experience a steep fertility decline that looks sudden.

This is especially common in certain toy and brachycephalic breeds.

What I Recommend as the First Diagnostic Steps

If a previously fertile male suddenly becomes sterile or produces only small litters, here’s the sequence I advise:

1. Full semen analysis

Identifies whether the issue is:

• sperm count

• motility

• morphology

• or complete absence of viable sperm

My Semen Analysis kit [with or without sperm microscope] is available here.

2. Prostate exam and culture

Rules out a very common, treatable cause of stud dog fertility problems.

3. Thyroid panel

Hypothyroidism is quick and inexpensive to diagnose.

4. Recheck semen in 60–70 days

Sperm cycles take time — what you see today is the result of events weeks ago.

Often, the cause is temporary and reversible.

Final Thoughts

Stud dog fertility problems can feel mysterious, but there is always a reason behind sudden male dog infertility — and in many cases, it’s heat stress, infection, or hormonal imbalance rather than permanent damage.

If your proven male suddenly stops producing puppies, don’t assume his career is over.  With a systematic approach, most breeders can identify the cause and restore fertility.

My breeder students in Elite Breeder Formula get ongoing help in issues like this, as well as a step-by-step plan to elevate their marketing into the Elite level of buyers.

Warmly,
Dr Meg Howe
Veterinarian & International Breeder Mentor
Elite Breeder Formula