The bonvine reproductive system has six primary parts: vulva, vestibule, vagina, cervix, uterus and ovaries. Each part plays a vital role in the estrous (also called estrus) cycle and reproductive life of the cow. Understanding the cow's anatomy and hormonal mechanisms is essential to effective animal husbandry. The bovine reproductive system has four primary functions: producing ova for fertilization, facilitating fertilization, gestating the fetus and birthing the calf.
The vulva is the only part of the cow's reproductive anatomy on the body's exterior. It protects not only the opening to the reproductive system, but also the opening to the urinary tract. The vulva reddens and swells in response to increases in estrogen and can indicate a cow is entering into her breeding cycle.
The vestibule is an area approximately 4 inches long between the vulva and the vagina. The urethra opens into the vestibule, making it the only part of the bovine reproductive system that is shared by two different bodily functions. The vestibule does double duty. It allows urine to pass out of the body and allows semen to enter the vagina and uterus.
A cow's vagina is about 6 inches long and connects the vestibule with the cervix. In natural mating, the bull deposits the semen in the vagina. In artificial insemination, the vagina is a guide for placing the semen in either the cervix or the uterine body. When the calf is born, the vagina becomes the birth canal to guide the calf out of the cow's body.
The cervix has different functions depending on the stage of the estrous and reproductive cycle. When the cow is not in estrous, the cervix acts as a tight cap protecting the uterus from injury and infection. When the cow is in estrous and ovulating, the cervix becomes chemically favorable for semen survival and storage, enhancing the chance for fertilization and pregnancy. When the cow is pregnant, the cervical secretions form into a thick mucous plug to protect the calf from infection.
The uterus is the organ that incubates the calf. The organ has a central chamber, or body, before dividing into two horns that lead to the ovaries. In a non-pregnant cow, the uterine body is less than 2 inches long. The first function of the uterus is to transport sperm to the uterine horns to fertilize the ovum. The second is to nourish and protect the calf during gestation. The third is to expel the calf through the vagina at birth.
The vulva, vagina and uterus are essentially specialized muscle groups that promote and support fertilization and gestation. However, the ovaries are the key to the bovine reproductive system. The ovaries have two functions. The first is to produce mature ova capable of fertilization. A cow has thousands of nascent ova. However, typically only one matures and releases at a time during estrous. The second function of the ovaries is to produce and regulate the cow's hormones necessary for estrous and pregnancy.