Anatomia reproductora

Reproductive Anatomy and Physiology of Cattle
Mel DeJarnette, Senior Reproductive Specialist Dr. Ray Nebel, Senior Reproductive Specialist

uccessful artificial insemination programs are based on a clear understanding of the anatomy and physiology of reproduction in cattle. Before attempting to inseminate cows, you must develop a mental picture of the anatomical parts that comprise the femalereproductive tract. In order to understand why an animal displays the many signs of estrus, when she should be inseminated, and how the pregnancy develops, you must clearly understand the hormonal mechanisms controlling the estrous cycle in cattle.

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“In order to understand why an animal displays the many signs of estrus, when she should be inseminated, and how the pregnancy develops, youmust clearly understand the hormonal mechanisms controlling the estrous cycle in cattle.”
deposited in the anterior portion of the vagina. The vagina will also serve as part of the birth canal at the time of calving. The cervix is a thick walled organ forming a connection between the vagina and uterus (Figure 2). It is composed of dense connective tissue and muscle and will be the primary landmarkwhen inseminating cattle. The opening into the cervix protrudes back into the vagina. This forms a 360º blind-ended pocket completely around the cervical opening. This pocket is referred to as the fornix. The interior of the cervix contains three to four annular rings or folds that facilitate the main function of the cervix, which is to protect the uterus from the external environment. The cervixopens anteriorly into the uterine body. About an inch long, the body of the uterus serves as a connection between the two uterine horns and the cervix. The uterine body is the site where semen should be deposited during artificial insemination. From the uterine body on, the reproductive tract separates and all further structures come in pairs (Figure 3). The two uter-

ANATOMY First, let’s lookat the parts that make up the reproductive system in cattle (Figure 1). There are two ovaries, two oviducts, two uterine horns, a uterine body, cervix, vagina and vulva. The bladder lies below the reproductive tract and is connected at the urethral opening located on the vaginal floor. The rectum is located above the reproductive system. The vulva is the external opening to the reproductivesystem. The vulva has three main functions: the passage of urine, the opening for mating and serves as part of the birth canal. Included in this structure are the lips and clitoris. The vulva lips are located at the sides of the opening and appear wrinkled and dry when the cow is not in estrus. As the animal approaches estrus, the vulva will usually begin to swell and develop a moist red appearance. Thevagina, about 6 inches in length, extends from the urethral opening to the cervix. During natural mating, semen is

Figure 1. Side view of the cow’s reproductive system.

Figure 2. Close-up view of the cervix.

▼ REPRODUCTIVE ANATOMY AND PHYSIOLOGY OF CATTLE

Figure 3. The short uterine body divides into two long uterine horns.

Figure 5. The UTJ, isthmus and ampulla are functionallydifferent regions of the oviduct.

ine horns consist of three layers of muscle and a heavy network of blood vessels. The main function of the uterus is to provide a suitable environment for fetal development. When a cow is bred, either naturally or by artificial insemination, the uterine muscles, under the influence of hormones oxytocin and estrogen, rhythmically contract to aid in spermtransport to the oviducts (Figure 4). Oviducts, as their name implies, carry ova, the cow’s eggs. The oviducts are also commonly referred to as the fallopian tubes. The oviduct has several distinct regions when examined microscopically. The lower segment, closest to the uterus is called the isthmus. The connection between the uterus and the isthmus is called the utero-tubal junction or UTJ. The UTJ...