Reproduction In Farm Animals: Female Reproductive System

Female Reproductive Tract - Cow (Courtesy:
The female not only contributes the female sex cell (ovum) but also provides the necessary environment in which the new individual is nourished during the early days of its life. These functions are performed by the primary and secondary organs of the reproductive system. A pair of ovaries are the primary organs of reproduction and produce not only ova but also the hormones required for the normal sexual behavior of females. The secondary organs of reproduction are a pair of oviducts (Fallopian tubes), the uterus, the cervix, the vagina, and the vulva. The mammary glands are also considered an accessory sex organ as they are closely related to the completion of reproduction by the nourishment of the young one.
The development of the reproductive organs starts before birth during the embryonic stage, but they remain quiescent. After birth, the reproductive organs develop gradually until the female attains a specific weight at a certain age when she becomes sexually mature, i.e. capable of producing viable gametes. The age at which a female becomes sexually mature is called puberty.
(a) Ovaries: The cow or buffalo has two ovaries situated on either side of the medial line, deep in the pelvic cavity almost at the border of the abdominal cavity. The right and left ovaries are connected with the uterine cornua of each side by tortuous Fallopian tubes. The ovaries of the buffalo are irregularly oval or spherical in shape and variable in size, while the ovaries of the cow are usually ovoid or spheroidal. The size and weight of active ovaries change frequently due to the formation of Graffian follicles and corpora lutea. A functional ovary develops from outer germinal epithelium from which the Graafian follicle develops.
The ovaries are the primary organs of reproduction because they produce not only the egg cells (ova) but also the sex hormones essential for female sexual activities. Willingness to mate (libido), ovulation, and many processes related to development, maintenance, and delivery of the calf are regulated by the female sex hormones. Hormone production in the ovaries is primarily controlled by the gonadotropic hormones of the pituitary gland. Under the stimulation of the pituitary hormones, the ovaries produce a follicular stimulating hormone (FSH), which is an estrogenic substance. Estrogens induce the psychic manifestations of estrus (heat). They also bring about glands of the cervix to secrete, and promote development of the mammary duct system. The characteristics behavior of the female and the secondary sex characteristics of the female are largely due to the influence of estrogens.
When ovulation takes place, the ruptured cells form the corpus luteum. The corpus luteum becomes a temporary endocrine organ under the influence of the luteinizing hormone  (LH) of the anterior pituitray. The corpus luteum secretes a hormone called progestrone which prepares the endometrium for the implantation of fertilized ovum and the maintenance of pregnancy. Progestrone also prevents ripening of additional follicles and ovulation, thus preventing the occurrence and manifestation of heat. It also stimulates the growth of the alveoli of the mammary glands and depresses the production of luteinizing hormone by the pituitary. The corpus luteum also produces another hormone known as relaxin, which causes decalcification of the pelvis. This results in the relaxation of the birth canal during parturition.
(b) Tubular Genitalia:
The tubular genitalia consist of the oviducts or Fallopian tubes, the uterus, the cervix, the vagina, and the vulva.
Oviduct or Fallopian tube. The oviduct is a tortuous, tubular structure of muscular and epithelial tissues. It reaches from the ovaries to the tapered end of the uterine horn. In cattle of different ages, the oviduct varies in length from 20 - 35 cm, while the length of the oviduct in buffalo varies from 20 - 25 cm. On the basis of diameter and internal structure, the oviduct consists of three parts: the isthmus or narrow portion which adjoins the uterine horns; the ampulla, which is slightly wider; and the infundibulum, which opens into the peritoneal cavity.
Uterus. The uterus consists of a body and two "horns". It is a muscular and irregularly tubular organ, the size of which increases during successive pregnancies. In heifers, it is situated 25 - 40 cm from the vulvular opening, just anterior to the cervix.
Cervix. The cervix or the neck of the uterus is a small muscular tube which extends from the uterus to the vagina. The muscular wall of the cervix is thick and its mucosa contain a large number of mucus-secreting cells. The mucosa form thick folds; opposite folds tend to overlap, forming a spiral passageway through the cervix. This makes possible the tight closure of the cervix with a cervical plug that is formed during pregnancy. This structure and secretions from the mucus secreting cells protect the uterus from microorganisms commonly present in the vagina. The cervical muscles relax during estrus and at the time of parturition. At parturition the cervix dilates, allowing the calf and fetal membranes to be expelled.
Vagina. The thin but elastic-walled tubular connection of the cervix with the vulva is called the vagina. It is a common passage for the reproductive and the urinary tract. The epithelial lining of the vagina undergoes changes during the estrus cycle. During natural breeding, semen is deposited in the vagina near the cervix.
Vulva. The external opening of the female genitalia is called the vulva. It includes the clitoris and the vestibule. The clitoris is a structure of erectile tissue (homologous with the male penis) located just inside the lower junction of the vulvular lips. The external opening of the reproductive tract of the cow lies just below the anus. It is about 12 cm long and has a wide, rounded dorsal angle and a narrow ventral angle. The thick labia majora are covered with fine hair.