Congenital Pet Defects

Congenital Pet Defects

From a Veterinarian's Perspective

An In-Depth Look with Dr. Ingrid Pyka


Abnormalities of the body that are present at the time of birth are called congenital defects. Such anomalies may involve any organ system or any part of the body.

Some may be minor and resolve with growth, while others may prevent normal development and function or even cause premature death.

Though certain defects may be quite obvious at birth, many may remain hidden for months, years, and some even lifelong.

Congenital defects can occur for no known reason, can be inherited, can be caused by environmental factors, or can be a combination of any of these.

Embryonal/Fetal Development

Defects can occur anytime in the developmental stages of the embryo or fetus. The occurrence or severity of the defect can depend on the stage of development when an insult occurs.  The earlier in the pregnancy an insult occurs, the more risk there is to the embryo or fetus.

Anomalies in the earliest stages of the embryo generally lead to embryonal/fetal death. During the first month of a dog or cat pregnancy, the fetus develops the majority of its organ systems. Abnormalities occurring within this period can cause serious functional defects.

The latter portion of the pregnancy focuses on growth and maturation of the already existing fetal body and its organs. Defects during this phase may be less severe. However, a few systems still undergo significant development during the second half of pregnancy, including the oral palate, cerebellum (the portion of the brain coordinating movement), urinary and genital systems. Abnormalities here can still produce serious complications.

Causes of Congenital Pet Defects


The cause of many congenital defects is unknown. Environmental circumstances during pregnancy may lead to a predisposition to certain defects.  Abnormalities to the maternal metabolism, trauma, or temperature extremes may cause problems in fetal development.  Examples of general congenital defects include cleft palates, polydactylism (extra toes), pectus excavatum (intrusion of the breastbone into the thoracic cavity), dwarfism, extra vertebrae, and hydrocephalus.

Exposure to specific infections, chemicals or drugs (known as teratogens) during pregnancy will also increase risks for specific birth defects. A drug called Griseofulvin, often used to treat ringworm, is one example of a medication with known teratogenic effects causing cleft palate in the fetus. Similarly, viral panleukopenia infection of the pregnant cat may result in cerebellar hypoplasia of the kittens, potentially producing brain damage with severe incoordination.

Some congenital defects are specific to certain breeds and are a result of exaggerated features that characterize the breed. Brachycephalic syndrome is most commonly seen in bulldogs, or other short-nosed breeds of dogs, and results in abnormal development of different parts of their airway.  Animals with these defects can have breathing difficulties leading to airway obstruction.  Another example is entropion, which is rolling-in of the eyelids, commonly seen in the Shar Pei.

Many animals with congenital defects can still maintain a high quality of life. Treatment options for abnormalities vary as for any health issue.

Many congenital abnormalities are believed to be inherited, although the exact mode of inheritance is often unknown.  Examples include portosystemic shunts in Yorkshire terriers, dilated cardiomyopathy in Dobermans, and kidney disease in Wheaten terriers.   Ragdoll cats have been known to have an increased tendency toward eyelid defects (colobomas) at birth.

Some congenital defects have been proven to be hereditary in certain breeds, being passed on through parental genes. The breed name is often included in the disease description.  Examples include Collie eye anomaly, Scotty cramp, and copper toxicosis in Bedlington terriers.

Detecting Congenital Pet Defects

Most external anatomical abnormalities are recognizable at birth or shortly after. Cleft palates, umbilical hernias, or limb deformities may be readily visible. Subtle abnormalities, such as heart murmurs caused by improperly developed heart valves, may require veterinary assessment for diagnosis.

Some defects, such as cryptorchidism (the failure of both testicles to descend into the scrotum) or dental issues, may take several weeks to months to become evident. A number of congenital defects, however, may not be detected until the animal gets much older. In such cases, it may be only abnormalities in routine screening tests that raise early concerns. 

Other times, it is not until suspicious medical issues develop that a diagnostic search is triggered. A “healthy” maturing puppy or kitten, for example, may have a congenital portosystemic shunt in the liver. It would not be until mental confusion, disorientation or seizures occur, or, until the pre-spay/neuter blood tests reveal abnormalities, that your veterinarian would run relevant additional testing.

Monitoring for Congenital Defects

As the cause of many congenital defects is unknown, preventing them can be difficult.  Having a thorough physical examination of your pet by your veterinarian can help detect potential abnormalities early in life.  If the abnormality can be modified or fixed, the earlier the problem is detected the better outcome for your pet.


Responsible breeders generally seek regular veterinary care and have a close relationship with their veterinarian.  Keeping the breeding animals up-to-date on vaccines, free from intestinal parasites, and on a balanced diet are all important factors in providing optimal health for the parent and offspring. If medications are necessary while the female dog is pregnant or lactating, the veterinarian may choose to alter the course of treatment for increased safety of the litter, or the veterinarian may advise not to treat at all. Even some vaccines can be detrimental to the fetus and may not be given. Often the veterinarian will recommend appropriate screening tests and/or prophylactic treatments.

Reputable breeders strive to eliminate carriers of specific congenital defects from their lineage. Registries have been established to list breeding animals screened as free from specific defects. The advent of DNA testing has also allowed registration of animals as being carrier-free of a particular gene.

Choosing a Pet

If you elect to adopt a specific breed, research the breed. Be aware of the known genetic defects. Research the breeder. Find out the lineage of the litter’s parents, preferably at least two to three generations back. Verify the breeder’s registration for absence of congenital defects.

Before you sign any sales contract, understand your options if a congenital defect (or any other health issue) is found. Observe the newborn for any unusual symptoms and report them to your veterinarian. Once you have chosen your puppy or kitten, whether it is purebred or a mix-breed, have your veterinarian perform a thorough physical examination immediately. Some breeders will allow you to have your veterinarian examine the animal prior to purchase.

Unless there is suspicion of a specific problem, generally puppies and kittens are not routinely tested for every known infection or systemic abnormality. Hence, some medical defects, though present at birth, may not be diagnosed until later in life. Follow your veterinarian’s recommendations for screening tests – especially prior to any anesthesia.

Many animals with congenital defects can still maintain a high quality of life. Treatment options for abnormalities vary as for any health issue. Whether or not a cure can be achieved through medications or surgery, your veterinarian will guide you with options that will optimize the quality of life for your companion.

Dr. Ingrid Pyka is the medical director at Harrison Memorial Animal Hospital in Denver, Colo., a non-profit veterinary hospital for qualified low income pet owners. As a veterinarian, Dr. Pyka emphasizes educating her clients to give them the tools to best care for their furry companions. She strongly feels that combining the highest quality medicine with complete client understanding allows patients and their owners to receive the best and most appropriate veterinary care.

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