Structure and Function of the Female Canine Reproductive Tract

Below is information about the structure and function of the female dog reproductive tract. We will tell you about the general structure, how it works in dogs, common diseases and common diagnostic tests performed in female dogs to evaluate the reproductive tract.

What Is the Female Canine Reproductive Tract?

The female dog’s reproductive tract consists of the female genital organs including the ovaries, uterus, vagina, vulva, and mammary glands.

Where Is the Female Canine Reproductive Tract Located?

The reproductive organs are located in the abdomen, and the mammary glands are located in two rows along the outside of the abdomen, running from the groin to the chest. The right and left ovaries are located just behind the kidneys. The ovaries are connected to the uterus by small ducts called oviducts. The uterus extends from the area behind the ovary to the back of the abdomen just in front of the pelvis. The uterus terminates at the cervix, which separates the uterus from the vagina. The vagina passes through the pelvis to the vulva, which is the external opening of the genital passage.

What Is the General Structure of the Canine Female Reproductive Tract?

Ovaries are suspended from the top of the abdomen by a broad ligament called the suspensory ligament. Oviducts are small tubes that extend from the ovaries to the uterine horns. At the end of the oviduct nearest the ovary a funnel-like structure, the infundibulum, catches the egg (ovum) when it is released from the ovary.

The uterus of the dog is Y-shaped, with the arms of the “Y” being longer than the stem. The long arms of the uterus are called the horns, and the short stem is called the body. The uterine horns extend from each ovary and join to form the body of the uterus. When the female is pregnant, the fetuses are arranged in a row in both horns. The very tip or base of the Y is the cervix.

The walls of the uterus are lined with a vascular and glandular lining (mucosa) and contain smooth muscle. The muscular substance of the uterus is called the myometrium; the inner lining is called the endometrium.

The cervix contains connective tissue and muscle that form a firm tube-like sphincter. The cervix is usually closed to prevent infection. During fertilization and birth the sphincter of the cervix is relaxed or opened.

The vagina of the bitch is very long and passes through the pelvis toward the vulva. In a 25-pound dog, the vagina averages 12 cm long and 1.5 cm in diameter. Both the length and diameter increase considerably during pregnancy and birth.

The vaginal walls are made up of an inner mucosal layer, a middle smooth muscle layer, and an external coat of connective tissue. The vaginal mucosa contains numerous folds, which allows for great expansion and stretching.

Mammary glands are composed of connective tissue to provide support and structure, blood vessels, lymphatic vessels and glandular tissue. Mammary glands contain small saclike glands that secrete and store milk. Milk eventually travels through a duct system to empty into the teat. The dog usually has five pairs of mammary glands.

What Are the Functions of the Female Reproductive Tract in Dogs?

The ovaries contain the eggs (ova) that are waiting to be fertilized. The ovaries also produce the female hormones of estrogen and progesterone. The eggs are released from small saclike structures called follicles during the process of ovulation and pass through the fallopian tubes into the uterus. When a bitch is spayed, the ovaries, oviducts, and uterus are removed.
The primary function of the uterus is reproduction. It serves as the site for implantation of fertilized ova (eggs) and for the growth and development of the fetus. The uterus houses the fetus until it is ready to be delivered.

The vagina provides a passage way from the outside of the body to the uterus. During breeding, sperm is deposited in the vagina by the male dog. The vagina provides a protected passage for fetuses to move from the uterus to the outside and also protects the opening of the urethra (where urine leaves the body).

The vulva protects the opening of the vagina and provides external markings that identify the animal as a female. The function of the mammary glands is to produce milk for any offspring.

What Are the Common Diseases of the Female Reproductive Tract?

Disorders of the reproductive tract may affect the ovaries, the uterus, the vagina, the vulva or the mammary glands. Each individual area is prone to different disorders.

Disorders of the Canine Ovary

• Ovarian cysts may develop from the accumulation of fluid within the follicles. These cysts may cause no clinical signs, the animal may fail to come into estrus (heat), or may show signs of continuous estrus.
• Ovarian remnants may sometimes occur when a portion of the ovary is cut and left behind during the spaying surgery. These dogs show recurrent signs of coming into heat at some time after the surgery has been performed.
• Tumors may develop in the ovaries and may be either benign or malignant.

Disorders of the Canine Uterus

• Metritis is inflammation of the uterus. This term is most commonly used when uterine inflammation develops after a pregnancy. It usually develops because of a bacterial infection that ascends up the vagina and gains entrance to the uterus through the open cervix.
• Pyometra disease is a complex problem of older female dogs that have not been spayed. The glands and the endometrium of the uterus become enlarged and predispose the uterus to infection. Bacteria may enter the uterus through the cervix and begin to grow in the uterus. The uterus gradually increases in size, filling with purulent material. If the cervix is open, discharge (pus) may drain from the vagina. If the cervix is closed, no discharge will be seen. Pyometra often occurs within eight weeks of the dog’s last heat cycle due to increased levels of the hormone progesterone. All unspayed dogs are susceptible.
• Uterine prolapse is the protrusion of the uterus through the cervix into the vagina. Portions of the uterus may be exposed at the vulva. It is an uncommon condition in the dog. It usually occurs during or immediately after giving birth, most often after the delivery of the last newborn, but can also be seen following spontaneous abortion.
• Tumors may develop in the uterus. There are many different types of tumors that can develop in this organ, both benign and malignant. Spaying, with removal of the uterus, prevents the development of uterine tumors.

Disorders of the Canine Vagina

• Vaginitis is inflammation of the vagina. It may occur in any age of dog, but a juvenile form is seen in dogs less than one year of age. The juvenile form of vaginitis often resolves after the first estrous cycle. Other causes of vaginitis include congenital defects, urinary tract infections; vaginal infections (bacterial, viral), vaginal tumors, and vaginal trauma. The primary clinical sign is vaginal discharge.
• Vaginal hyperplasia or edema is an exaggerated response by the vaginal tissue to estrogen during certain phases of the estrus (heat) cycle. The vaginal tissue becomes swollen and may protrude through the vulva, and appear as a donut-shaped mass. Vaginal hyperplasia is most common in young intact female dogs and is more common in the boxer, Bulldog, Saint Bernard, German shepherd dog, and certain other breeds.
• Tumors may also develop within the vagina. One form of tumor, the transmissible venereal tumor (TVT) is caused by a virus. TVT is a contagious condition and is often spread during breeding.

Disorders of the Canine Mammary Glands

• Disorders of milk production include galactorrhea (milk production that is not associated with pregnancy), agalactia (the failure to secrete milk at appropriate times), and galactostasis (the abnormal collection of milk in the mammary glands).
• Mastitis is inflammation and/or infection of the mammary glands. In most cases, bacteria are believed to travel up the mammary ducts into the glands. The glands then become painful, red, and sometimes swollen.
• Mammary gland tumors are the most common tumor to develop in female dogs, particularly in those that have not been spayed. Mammary gland tumors are frequently malignant, although some do not behave very aggressively. Spaying the dog before its second heat cycle can effectively prevent these tumors.

What Types of Diagnostic Tests Are Used to Evaluate the Female Reproductive Tract in Dogs?

• A complete blood count, organ profile, urinalysis, and urine culture are often used to look for evidence of infection or other related organ abnormalities (e.g. bladder infection, kidney disease, etc.).
• X-rays of the abdomen are useful to identify enlargement of the uterus. If the ovaries and uterus are a normal size, then they usually do not show up on plain X-rays.
• Chest X-rays may be indicated if a tumor is present, in order to search for metastasis.
• Vaginoscopy is the examination of the vulva and vagina by introducing a scope through the external genitalia directly into the vagina to examine the area for evidence of tumors and inflammation.
• Vaginal cytology can be performed by retrieving cells of the vagina using a sterile cotton swab and examining those smears under the microscope. Vaginal cytology is helpful to identify where in the heat cycle the dog might be and to search for signs of inflammation and infection.
• Cytology can also be performed on milk samples.
• Ultrasonography of the abdomen is very helpful in evaluating the internal organs of the abdomen using high frequency sound waves. Ultrasonography can often identify organ changes that do not show up on X-rays. It can also be used to confirm the presence of a pregnancy.
• Bacterial culture and sensitivity testing may be performed. Material is retrieved using a special culture swab or collection tube, and attempts are made to grow the bacteria and identify them. Several antibiotics are then tested on the bacterial culture to determine which antibiotic works best to kill the bacteria.
• A fine needle aspirate and examination of the cells is often useful when assessing masses or tumors.
• Biopsy of masses and abnormal tissue may also be performed.
• Removal of the organ and submitting it for biopsy may be needed in some cases to identify the underlying problem and its cause.