Infertility in dogs – causes, investigations and treatment

Overview

Conception and maintaining pregnancy are different stages

Producing a litter requires ovulation, fertile sperm and their meeting at the right time. The female must also maintain a pregnancy lasting around 2 months. Failure to conceive and loss of an established pregnancy are therefore distinguished.

Eggs developing in ovarian follicles are released at ovulation. The corpus luteum formed after ovulation produces progesterone. Its concentration is therefore monitored to time reproduction, although it is not specifically a pregnancy hormone.

A large French study found an expected whelping rate of 81.9%. This is not a permanent infertility rate. Permanent infertility cannot be inferred from one unsuccessful mating because timing and completion of mating are checked first.

Causes

Timing, ovaries and uterus

An egg cannot be fertilised immediately after release. Fertilisation capacity is usually reached 48–83 hours after ovulation. Automatically mating on days 12–14 after the start of oestrous bleeding may miss the individual's fertile period.

Ovulation may fail despite outward signs of oestrus. An ovarian cyst or tumour can instead sustain prolonged oestrus. Cystic endometrial hyperplasia makes the uterine environment less suitable for embryo implantation. Inflammation of the uterine lining can also be associated with reproductive failure.

Anovulatory cycles account for an estimated 1% of seasons. They do not usually impair fertility at the next season. A congenital vaginal septum or narrowing can prevent successful mating. A considerable size difference between dogs can also make natural mating difficult.

Sperm and a male's ability to mate

A male's problem can involve sperm production, transport or storage. Testicular and prostate diseases can impair semen quality. Pain can also prevent mating despite preserved sexual interest. A hip or knee problem, for example, can make positioning difficult. A congenital fold restricting penile movement, called a persistent frenulum, can cause abnormal bending and pain.

Risk factors

Ageing can reduce female fertility and litter size. In a study of 240 females, cystic endometrial hyperplasia affected fewer than 7% of those younger than 2 years and more than 60% of those older than 6. These figures concern endometrial changes, rather than infertility in every dog of those ages.

Ageing in a male can reduce sperm motility, normal structure and viability. Excess weight has been associated with poorer conception and smaller litters. Underweight females may have irregular seasons. Inbreeding has been associated with smaller litters in some breeds, but its effect is not the same in every breed.

Typical symptoms

A fertility problem may appear in reproductive outcomes without other obvious signs of disease. Observations prompting investigation include:

• A female fails to become pregnant despite mating.
• Seasons are irregular or appear absent altogether.
• Signs of oestrus continue unusually long rather than ending normally.
• A male is unwilling or unable to mate.
• Blood is visible in semen.
• Testicles change size or become tender.

Oestrus confirmed through cytology and continuing beyond 21 days is classified as prolonged. In a silent season, however, the hormonal cycle may function without noticeable bleeding or swelling. An owner may then mistake a normal cycle for an absent one.

A young female's first season may also stop after a brief onset and restart days or weeks later. This split season is distinguished from continuously prolonged oestrus.

Complications and consequences

The underlying disease determines the health risk

Cystic endometrial hyperplasia can predispose to uterine infection. Uterine inflammation can cause early pregnancy loss. Severe testicular or epididymal inflammation can leave the testicle atrophied or scarred. Such permanent damage can permanently reduce sperm production and fertility.

Brucella canis usually causes persistent, often lifelong infection. It reduces female fertility. It can also cause foetal deaths. Infection can pass to people as well. It is therefore an infectious disease issue extending beyond reproductive results.

Diagnosis at the vet

Both dogs are examined

The history covers previous litters, matings, illnesses and medication in both dogs. The male's previous successful breeding is reviewed separately. General examination also looks for pain interfering with mating. The female's vaginal anatomy, uterus and ovaries are examined. In the male, assessment includes the testes, penis and prepuce.

Failure to conceive may be the only observed problem with endometritis. Uterine fluid visible on ultrasound after oestrus can support suspicion of inflammation. More detailed investigation may require uterine cytology or biopsy. A vaginal culture does not reliably establish what is in the uterus.

Cycle monitoring and pregnancy diagnosis

Vaginal cytology helps assess cycle stage. Repeated progesterone measurements help identify ovulation. Different assays nevertheless give different results for the same sample. Interpretation therefore considers the method's reference values and changes over time. Ultrasound can monitor follicle growth and ovulation.

Pregnancy can be checked by ultrasound around 30 days after mating. Relaxin may be detectable in blood 22–27 days after mating. A negative test performed too early can be false. Progesterone, by contrast, is also produced without pregnancy, so a cycle-monitoring hormone result does not establish the presence of puppies.

Relaxin is not produced in phantom pregnancy, when no placenta develops. A positive relaxin result does not, however, show that developing puppies are alive. Conception and continuation of pregnancy are therefore assessed at separate visits where necessary.

Semen and infection testing

Semen assessment examines sperm numbers, motility and structure. If sperm are absent, the first question is whether ejaculation was successful. Impaired sperm production or an obstruction of the transport route may be responsible. In rare retrograde ejaculation, sperm enter the bladder.

A positive vaginal or semen bacterial culture alone does not establish an infection needing treatment. The sample is assessed alongside signs and cytology. Antibody testing is the primary screening method for Brucella infection without signs.

More than 65% progressively motile sperm has been associated with good fertilisation results. A normal morphology proportion above 60–70% has also been proposed. These are indicative observations linked to reproductive outcomes, rather than proof of fertility. A single testosterone result is difficult to interpret because production varies during the day.

A urine sample collected after semen collection can investigate retrograde ejaculation. Numerous sperm in the bladder support this suspicion.

Treatment

Addressing a demonstrated cause

Your vet selects treatment according to the cause identified through investigations. For a timing problem, care centres on ovulation monitoring and planning mating accordingly. Fresh normal sperm can survive in the female reproductive tract for 7–9 days. Timing is particularly precise when frozen semen is used.

A diagnosed hormonal disorder may be treated with hormones regulating ovarian function. There is no single established treatment for endometritis. Cystic endometrial hyperplasia can worsen prognosis because treatment options are limited.

An antibiotic for bacterial infection is selected after investigating the organism. Finding Mycoplasma in a healthy male does not by itself establish the cause of infertility. Chronic prostatitis treatment must also address associated prostatic enlargement. A large prostate abscess may need surgical drainage.

An identified vaginal septum can sometimes be removed during endoscopy. Semen collection may be repeated in a more suitable setting if the first sample was incomplete. Treatment therefore distinguishes true impaired sperm production from a situation where sperm were simply not obtained in the sample.

Goals of treatment and breeding

Bacterial shedding and signs can return despite brucellosis treatment. An infected dog is not bred from, and preventing spread guides further action. Some breeding guidelines state that artificial insemination should not compensate for a dog's unwillingness or inability to mate normally. The medical possibility of producing puppies and suitability for breeding are therefore assessed separately.

Prevention

Before breeding, both dogs' health and ability to reproduce naturally are assessed. A body condition score of 4–5 on a 9-point scale is recommended for the female. Cycle monitoring helps reduce timing errors.

Some national guidance recommends Brucella antibody testing for imported dogs and foreign dogs used for breeding. Vaccinations and other routine health care are checked before mating. Inherited reduction in fertility is considered in breeding choices.

Uterine involution after birth takes around 84 days, or almost 3 months. A short interoestrous interval may therefore require missing 1–2 seasons before planning another litter. Under one breeding registration scheme, the usual minimum interval between litters' births is 10 months. A female younger than 8 years at mating is allowed one shorter birth interval under those rules.

Important for dog owners

Bring a season calendar and both dogs' records

Record season onset and duration, mating dates and previous pregnancy tests. Bring hormone results with sampling dates and the laboratories used. Describe how mating took place and any male pain or reluctance. A copulatory tie is not essential for conception. It also does not prove mating was successful. Do not forcibly separate dogs while tied.

Under the registration scheme described above, the minimum breeding ages are 12 months for a male and 18 months for a female. Mating a female aged 8 years or older requires veterinary certification of health and good condition. The certificate is issued before mating and must be no more than 6 months old at mating. Agree the aim of investigations: treating disease, correcting timing or assessing whether breeding should be abandoned.

Under that scheme, a litter from a female aged 10 years or older at mating is not registered.

Frequently asked questions

Does one failure to conceive mean permanent infertility?

Not necessarily. Incorrect mating timing is the most common reason a female fails to conceive. Mating completion and cycle monitoring are investigated first. Male fertility is then assessed alongside the female because either partner may be involved.

Should only the female be investigated?

Both dogs' reproductive health is assessed. Semen is examined for sperm numbers, movement and structure. Mating-related pain can also prevent success despite normal female cycles and test results and previous litters from the male.

Does a progesterone result prove pregnancy?

Progesterone helps time ovulation during cycle monitoring. It is produced by the corpus luteum even without pregnancy. An established pregnancy and developing puppies are confirmed separately, for example through veterinary ultrasound, so raised progesterone alone is not considered proof of pregnancy.

Does a positive bacterial culture always need antibiotics?

Not automatically. A male with normal semen can also have a positive culture. The result is assessed alongside signs and cytology. Medication therefore targets a demonstrated infection-related problem rather than a bacterium's mere presence in a sample.

Does artificial insemination solve every mating problem?

No. Fertilisation depends on semen quality as well as timing. Some breeding guidelines require breeding dogs to be willing and able to mate naturally. Under those guidelines, artificial insemination is not used to bypass the requirement when a dog is unwilling or unable to mate normally.