Beginners Guide To The Cow Reproductive System

Cows have a reproductive system that is not dissimilar from humans. With cows, it's an 8-inch long passageway that lubricates and protects the rest of the reproductive system from bacterial colonization and foreign contaminants.

Understanding the anatomy of a cow’s reproductive system allows for better insight into the fertilization process, gestation, calving, and subsequent lactation which is a cyclical process that farmers must oversee.

This process is perhaps the most important thing for farmers to understand about cows, as it is vital for both beef and dairy cows to produce healthy calves each year for optimal productivity.

This article will explain the reproductive system of cows in a straightforward manner, including all the relevant facts that a beginner needs to know.

Parts Of A Cow Reproductive System

A cow’s vagina is part of the reproductive tract of a cow. It is an 8-inch long passageway that lubricates and protects the rest of the reproductive system from bacterial colonization and foreign contaminants.

It serves as a receptacle during copulation with a bull, as well as a canal through which a calf is birthed.

A cow’s reproductive system is comprised of several body parts that work together to allow for a cow to get pregnant and subsequently give birth. Understanding the purpose of each part of the reproductive tract is vital for understanding how the fertilization process works.

Aside from the vulva, everything else is inside the cow’s body and located underneath the rectum. This positioning makes rectal palpations possible.

A ligament attaches the cow’s uterus, oviducts, and ovaries, which are located in the pelvic area of the cow and suspended to allow for ease of movement and later to accommodate a growing fetal calf.


The vulva of a cow is the only part of the reproductive tract that is located outside of the body.

This genital structure is comprised of folds of skin that change in appearance depending on the number of hormones such as estrogen that may be present. The vulva will often swell during estrus (when a cow comes into heat and is ready for breeding).

A red color will become prominent in this area as it experiences an increased amount of blood flow, and this color change is one of the best signs that farmers can look for when determining if a cow is in estrus.


Roughly 4 inches long, the vestibule is a shared structure between the urinary system and reproductive tract. Knowledge of the location of the vestibule is important because it is possible to cause injury to a cow when attempting artificial insemination if an inseminating rod is accidentally placed into it.

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A blind sac is located just underneath the opening of the urethra where urine is released from the cow’s bladder and is called the suburethral diverticulum. It is important to bypass this structure and continue further into the cow’s vagina to deposit semen.

Cow Vagina

The cow vagina is an 8-inch long passageway located between the cervix and opening to the bladder and is the location of semen deposit during copulation with a bull.

The cow vagina also stretches to accommodate passing a calf during the birthing process.

The vagina likewise serves to kill bacterial invasion by the secretion of fluids that mix with cervical mucus to form a barrier that stops harmful bacterial growth from flourishing.

It is incredibly important to house cows in sanitary environments and to use clean inseminating equipment, lest vaginal infection occur. If a cow’s vagina becomes infected due to poor hygiene practices or urine pooling near the cervix, it can lead to infertility.


The cervix is located at the end of the cow’s vagina and is roughly 4 and a half inches long by 1 and a half inches wide. It serves as the opening to the uterus but has a protrusion to protect the uterus from harm.

Cervical walls are dense and thick, with rough ridges and rectal palpation will allow these annular folds to be distinguished from surrounding tissue and manipulated through the rectum in order to allow entry into the uterus by an insemination rod.

The anterior portion of the cervix is the prime location for semen deposits during AI procedures, as it holds and protects semen, allowing sperm to survive. Cervical mucus acts as a transport for sperm into the uterus, while also protecting against bacteria and keeping all foreign matter out.

A plug is formed naturally within the cervix canal to restrict further access once pregnancy is assured. Care must be taken to not insert an insemination rod through this plug, lest it cause unintentional abortion of the fetal calf.


The uterus is a structure that has a main cavity and two branches. As mentioned earlier, it is suspended by a broad ligament. The uterus is quite small when not harboring a fetus, and the main cavity measures a mere 2 inches.

The goal during artificial insemination is to place all sperm within this main cavity, as this allows for the greatest chance of pregnancy occurring. If the inseminating rod is pushed too far, it may deposit semen into one of the branches and not the main cavity.

An egg is released through one of these branches and migrates into the main cavity.

If semen was deposited into one of the branches, there is only a 50% chance that semen unites with the egg to produce a calf. On the other hand, if all the semen is deposited into the main uterine cavity, the released egg from either side would end up coming into contact with the semen.

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The uterus has several vital roles in reproduction. Uterine muscles are responsible for moving sperm into the oviduct after insemination occurs, as well as pushing the calf out during the birthing process.

The uterus secretes a nutrient-dense fluid called uterine milk which assists a developing embryo during attachment to the uterine wall and prior to the creation of the placenta.

The placenta allows for calf and cow to exchange nutrients and waste via caruncles and cotyledons which act as areas that create a pathway for the exchange.


Oviducts are also known as fallopian tubes and are around 10 inches long. They connect an ovary with one of the uterine branches and serve to catch and transport eggs during ovulation into the main cavity of the uterus.

Fertilization of the egg takes place in the ampulla which is the large, upper end of the oviduct, before being moved to the uterus over a period of 3 to 4 days.


The ovaries are the main organ of reproduction in cows and contain thousands of ova which can be turned into eggs. A cow’s ovaries measure 1 and a half inches long by 3/4 inches wide and are suspended by the broad ligament.

They are found at the narrow end of the oviduct, and are responsible for producing eggs, regulating hormones during pregnancy, and managing the estrus cycle.

Under normal circumstances, one ovum is produced from the thousands of ova contained in the ovaries during the estrous cycle. If more than one is released it can lead to multiple births which are generally not desirable.

The exception is if a cow has been injected with PMSG (pregnant mare’s serum gonadotropin) or FSH (follicle stimulating hormone), which are required during embryo transfer and can result in superovulation.

The ovaries are ultimately responsible for the beginning of the entire reproductive process by producing eggs and releasing them at the right time during the estrus cycle for pregnancy to occur.

Fertilization Process

The fertilization process can occur naturally if a bull is allowed to mate with a cow during the right time of her estrus cycle, or can occur through artificial insemination.

Most cows are bred through AI nowadays as it maximizes efficiency and increases the likelihood of conception.

However, in order for AI to be successful, it is imperative that a farmer know how to detect changes within the estrus cycle in order to inseminate a cow at the proper time. Also important are the way the cow and semen are handled, coupled with a proper insemination technique.

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Timing of Artificial Insemination

Timing is everything when it comes to AI. Farmers should track the estrus cycles of cows and synchronize them to figure out the insemination window during the heat cycle when conception is most likely to occur.

The best time is between 12 and 16 hours when standing heat has begun.

Cow Preparation

It is vital to keep a cow calm. Stressed cows can cause injury to themselves during insemination as well as cause rod displacement, leading to an unsuccessful attempt.

Heifers are more likely to need extra time as they aren’t used to this process. Be patient and wait until she has calmed down.

Once the cow or heifer has been calm for a few minutes, restrain her so she cannot move during the procedure.

Straw Preparation

It is important to have a container of water set aside at 35 degrees celsius. Straws containing semen should be taken out using forceps and placed in the warm water briefly to thaw for around 45 seconds.

The straw then should be dried and placed into a gun that has been properly preheated. The crimped end of the straw should be cut and the plunger of the gun should be pressed slowly and carefully until the semen is located at the tip of the straw.

Proper Insemination Technique

The vulva of the cow should be cleaned with a paper towel. It is important that an arm-length glove is placed on one arm, and lubed carefully. Insert your glove-covered arm into the rectum and dispose of any dung found within.

Use palpation within the rectum to locate the cervix of the cow. It is important to wipe down the vulva a second time before inserting the gun.

The gun should be nearly vertical to the entrance, held roughly between 30 and 40 degrees.

The gun should be slowly guided to the cervical entrance. Palpation through the rectum should allow for the tip of the gun to slide into the cervix.

Once the gun has passed the cervix, insert the semen into the main cavity of the uterus over the course of 5 seconds, taking care not to press too far – you don’t want to insert it into one of the branches.

Slowly and carefully remove the gun through the cow’s vagina to avoid injury.

Equipment Hygiene

It is vital that all equipment is properly cared for so bacteria and other contaminants are not spread through the herd.

Soiled guns and equipment need to be disinfected in boiling water. Straws should not be split, and AI sheaths should not be re-used.

It is also vital to use a new, clean glove for each cow. Discard any used gloves to prevent cross-contamination.

Christina Pichler

A longtime resident of Southern California, Christina spent her childhood summers on a farm, raising and caring for cows owned by her grandparents, which prompted a lifelong love of cows, and other farm animals. Christina is passionate about writing, having written hundreds of articles for well-known websites, and uses her English degree in service of her love for animal welfare, most recently taking on a writing position at Cow Care Taker in 2022.

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