Cattle are sexually mature at about the age of thirteen months, and they usually breed at thirteen to twenty-six months. They breed in a natural settings and polygyny (males mating with more than one female) has been observed. Dominant males compete for the females. They are dioecious, meaning male and female reproductive organs are in separate animals. Cows mate all year round, but more calves are born in the spring. Fertilization and development take place within the female body and developing embryos get nourishment from the female. One calf is born after about nine months of gestation and the young are relatively mature at birth. Cattle nurse for approximately six months. The maximum lifespan is more than twenty years, but the natural life span is generally not fulfilled. The average life is about three to four years before being sold for beef.
Their Reproductive Tract (Female)
Except for the vulva, all parts of the reproductive tract are located within the body of the cow. Parts of the reproductive tract include the vestibule, vagina, cervix, uterus, oviducts and ovaries. The internal parts are located beneath the rectum, which allows rectal palpations of the tract to be done easily. The uterus, oviducts, and ovaries are attached to a ligament and suspended in the cow’s pelvic area. This suspension allows these organs to move freely in the pelvic canal and into the body cavity, providing space to accommodate a growing fetal calf.
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| Diagram of the reproductive tract of a female cow |
Vulva
The vulva is the external part of the reproductive tract. The thickened folds of skin of the structure are sensitive to changes in oestrogen, the hormone responsible for estrus (heat). Swelling and redness of the vulva, due to increased blood flow, can be useful in oestrous detection when coupled with other signs.
Vestibule
The vestibule is a part of the reproductive tract shared with the urinary system. It is approximately 4 inches long. Openings from the urinary bladder and a blind sac located below the opening of the urethra called the suburethral diverticulum are located on its floor. Dairy producers and Al technicians can prevent insertion of an inseminating rod into these openings, which could result in injury or insemination failure, by knowing their location.
Vagina
The vagina is located between the opening to the bladder and the cervix. Approximately 8 inches long , it is the site of semen deposition during natural service. The vagina also serves as an nonrestrictive passageway for the calf at time of birth. One important function of the vagina is as a line of defense against invasion by bacteria. The epithelium of the vagina secretes fluids which combine with cervical fluids to inhibit growth of undesirable bacteria.
Protection from infections may not be sufficient when unsanitary housing conditions are prevalent, or dirty inseminating equipment is used. As a result, vaginal infections can be a problem. In addition, pooling of urine in the vagina adjacent to the cervix can cause infertility in some older cows.
Protection from infections may not be sufficient when unsanitary housing conditions are prevalent, or dirty inseminating equipment is used. As a result, vaginal infections can be a problem. In addition, pooling of urine in the vagina adjacent to the cervix can cause infertility in some older cows.
Cervix
The cervix is a unique structure within the reproductive tract. It is 4 to 5 inches long and 1 to 2 inches in diameter and lies between the vagina and uterus. This structure is designed to restrict access to the uterus. The area around the opening of the cervix actually protrudes back into the vagina. This protrusion deflects such things as inseminating rods away from the cervical opening if care is not taken during insemination.
Also, the walls of the cervix are thick and dense in comparison to the walls of the vagina. Three or four ridges or rings within the body or the cervix, called annular folds, can be distinguished by rectal palpation. The folds must be manipulated rectally while an inseminating rod is passed through to the uterus.
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| The cervix and a small portion of the uterus has been cut open. Note the thick folds of the cervix. |
The cervix has important functions. The anterior cervix may serve as a site for semen deposition during artificial insemination (Al). This occurs on services where the cycle length is not 21 days and pregnancy from a previous service is possible. Whether by deposition following Al or by migration from the vagina after natural service, the cervix acts as a reservoir for semen. The cervix provides a favorable environment for sperm survival.
Uterus
The uterus consists of a “body” and two “horns”. It is attached to the broad ligament and suspended within the pelvic cavity and posterior portion of the body cavity. The body of the uterus is adjacent to the cervix. In a non-pregnant state it extends less than 2 inches before it divides into two separate horns.
The uterine body is the major site of semen deposition during Al. If the tip of the inseminating rod is inserted too far into the uterus, semen is deposited in only one of the uterine horns . If the egg was released from the ovary on the other side, there is little chance that sperm and egg would unite.
The uterus has many functions. Its walls are composed of several layers of muscle which aid in transport of sperm to the oviduct following insemination and in expulsion of the calf at birth. Certain glands within the walls of the uterus secrete a fluid, uterine milk, which provides nutrients to the developing embryo before and after its attachment to the uterine wall.
The uterus also develops the maternal side of the placenta to nourish and protect the developing fetus. Its surface contains many specialized areas called caruncles . Cotyledons of the fetal placenta interlock with caruncles on the uterus to provide a passageway for the exchange of nutrients and waste between fetus and cow.
The uterus has many functions. Its walls are composed of several layers of muscle which aid in transport of sperm to the oviduct following insemination and in expulsion of the calf at birth. Certain glands within the walls of the uterus secrete a fluid, uterine milk, which provides nutrients to the developing embryo before and after its attachment to the uterine wall.
The uterus also develops the maternal side of the placenta to nourish and protect the developing fetus. Its surface contains many specialized areas called caruncles . Cotyledons of the fetal placenta interlock with caruncles on the uterus to provide a passageway for the exchange of nutrients and waste between fetus and cow.
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| Cotyledon |
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| Caruncle |
These 2 pictures shows the lining of the uterus showing caruncles on the surface (a) .The caruncles interlock with the cotyledons (b) on the fetal placenta to provide a passageway between the cow and the fetus for transfer of nutrients waste products.
Oviduct
The oviducts are approximately 10 inches long, 1/4 inch in diameter and lie between each ovary and tip of the adjacent uterine horn. The ovarian end of the oviduct is funnel shaped and called the infundibulum. The infundibulum catches the egg as it is released from the ovary at ovulation and moves it to the enlarged upper end of the oviduct called the ampulla. Fertilization occurs here within 12 hours of ovulation. After fertilization, the fertilized ovum is transported to the uterus in a process requiring 3 to 4 days.
Ovaries
The ovaries are the primary reproductive organ of the female. In a dairy cow, each ovary is approximately 1.5 inches long and 3/4 inch in diameter . The ovaries are suspended from the broad ligament near the end of the oviduct and lie near the tips of the curved uterine horns. Their function is to produce the egg or ovum and hormones involved in regulating the estrous cycle and pregnancy.
The ovaries contain thousands of ova. These are produced by the enbryo prior to birth.While the potential to collect thousand of ova from a cow exists, only one ovum is usually released during each estrous cycle.All ova are surrounded by a special layer of cells in the ovary.The growth of these cells produces blister-like structires ,called follicles, that are visible on the surface of the ovary.
Following ovulation, the walls of the follicle collapse and develop into the Corpus Luteum (CL) or yellow body. The CL reaches its maximum size 10-12 days after ovulation and is the dominant structure on the ovary. If a pregnancy does not result, the CL regresses 3 to 4 days prior to the next ovulation. However, the presence of an embryo in the uterus prevents this from happening.
Development of the follicle and subsequent formation of the CL are associated with the production of estrogen and progesterone, respectively. Estrogens are produced by the cells lining the wall of the follicle and are responsible for changes in behavior as well as altering the production of fluids by the vagina, uterus and cervix. In addition, estrogens also trigger the release, from the pituitary gland, of the hormone responsible for ovulation, Luteinizing hormone (LH).
Associated with ovulation is the transformation of the follicle wall into the CL under the influence of LH. The CL begins to produce progesterone which is required for maintenance of pregnancy. Progesterone acts upon the lining of the uterine wall to prepare it for subsequent attachment of the embryo. In addition, progesterone and low levels of estrogen prevent resumption of normal cyclic activity and allow for maintenance of pregnancy.
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| Ovaries of the dairy cow. Note the blisterlike follicle on the left ovary. The large structure on the right ovary is a corpus Iuteum. It is yellowishorange. A fully developed corpus Iuteum will occupy a major portion of the surface and body of the ovary. |
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| Ovary cut to show relative size of mature CL. Most of the CL is located within the body of the ovary. This structure produces and secretes progesterone, the hormone responsible for maintenance of pregnancy. |
Their Reproductive System (Male)
The reproductive tract of the bull consists of the testicles, secondary sex organs, and three accessory sex glands. These organs work in concert for formation, maturation and transport of spermatozoa, which are eventually deposited in the female reproductive tract. The secondary sex organs are the epididymis, vas deferens and penis. The three accessory sex glands include the seminal vesicles, prostate and bulbourethral gland (Cowper's gland).
Testicle
The testicle is located outside the body cavity in the scrotum and has two vital functions: producing the spermatozoa, and producing the male hormone, testosterone. Location of the testicles exterior to the body cavity is essential for normal sperm formation, which occurs only at 4 degrees to 5 degrees below body temperature. The scrotum provides physical protection to the testicle and helps regulate the temperature for optimum spermatozoa development. This regulation is done by coordination of three structures: a temperature-sensitive layer of muscle located in the walls of the scrotum, which relaxes when hot and contracts when cold; the external cremaster muscle within the spermatic cord, which controls the proximity of the testicle to the body by lengthening or shortening depending on environmental temperature; and a counter-current temperature exchange regulated by a blood flow process known as the pampiniform plexus, which is a coil of testicular veins that provide an effective mechanism for cooling arterial blood entering the testicle and transferring its heat to the venous blood leaving the testicle.
The testicle contains many long, tiny, coiled tubes known as seminiferous tubules, within which the sperm are formed and begin to mature. Scattered throughout the loose connective tissue surrounding the seminiferous tubules are many highly specialized cells, the interstitial cells of Leydig, that produce testosterone. There are hundreds of individual seminiferous tubules in the body of the testicle which unite with one another to form a few dozen tubules that exit from the testicle and pass into the epididymis.
Epididymis
The epididymis is a compact, flat, elongated structure closely attached to one side of the testicle. It is divided into three regions, the head, body and tail. The many tubules entered the head of the epididymis from the testicle unite to form a single tubule some 130 to 160 feet in length. This tubule is convoluted and packed into the 6- to 8-inch epididymis. Four major functions occur in the epididymis, including the transport of the developing sperm cells from the testicle to the vas deferens; the concentration of the sperm by absorption of surplus fluids; the maturation of the developing spermatozoa; and the storage of viable sperm cells in the epididymis tail.
Vas deferens
The vas deferens, also known as ductus deferens, emerges from the tail of the epididymis as a straight tubule and passes as part of the spermatic cord through the inguinal ring into the body cavity. Sperm are transported further along the reproductive tract to the pelvic region through the vas deferens by contraction of the smooth muscle tissue surrounding this tubule during ejaculation. Bulls may also be sterilized by a vasectomy in which a section of the vas deferens is removed so that sperm cannot pass to the outside of the body.
Urethra
The two vas deferens eventually unite into a single tube, the urethra, which is the channel passing through the penis. The urethra in the male serves as a common passageway for semen from the reproductive tract and urine from the urinary tract.
Accessory glands
Two of the accessory glands are found in the general region where the vas deferens unite to become the urethra. Secretions from these glands make up most of the liquid portion of the semen. In addition, the secretions activate the sperm to become motile. The seminal vesicles consist of two lobes about 4 to 5 inches long, each connected to the urethra by a duct. The prostate gland is located at the neck of the urinary bladder where it empties into the urethra. The prostate is relatively small in the bull, as compared to other species, and does not produce a very large volume secretion.
The third accessory gland, the Cowper's glands, are small, firm glands located on either side of the urethra. The clear secretion that often drips from the penis during sexual excitement prior to service is largely produced by these glands and serves to flush and cleanse the urethra of any urine residue that may be harmful to the sperms.
Penis
The penis is an anatomical structure that provides a means by which the penis is held inside the sheath except during time of service. Strong retractor muscles hold the penis in the "S" shaped configuration. Occasionally these muscles are too weak to function properly and a portion of the penis and sheath lining protrude at all times. This exposes the male to the danger of injury.
The penis is the organ of insemination. Spongy-type material within the penis is filled with blood during sexual arousal, resulting in erection of the organ. The end of the penis is the glans penis and is richly supplied nerves, which are stimulated during copulation to induce ejaculation.
~MooMoo
