Back to: Animal Husbandry SS 2
REPRODUCTIVE PROCESS IN LIVESTOCK MAMMALS AND POULTRY
The reproductive system includes all the organs and tissues concerned with reproduction in animals. Reproduction is the ability in animals to give birth to young ones. The purpose of reproduction is to ensure continuity of life.
Farm animals reproduce sexually and are mostly viviparous because they bear their young ones alive. Poultry birds on the other hand are oviparous because they produce their young ones by hatching eggs after an incubation period.
Male Reproductive System: The male reproductive system (Fig. 3.3) includes the testes which produce the spermatozoa and sex hormone called testosterone which aids the development of male sexual secondary characteristics. The spermatozoa are specifically produced in the seminiferous tubules of testes during meiotic cell division by a process called spermatogenesis. The testes are suspended or protected by scrotal sac (scrotum) outside the abdominal cavity to enable sperm cells to be produced at desired temperature.
The epididymis ensures the storage and maturation of sperm cells in the testes. The testes are connected to the uterus masculinus by vas deferens which transports sperms from testes to the uterus masculinus where mature spermatozoa are stored until they are released during coitus or mating. Blood vessels called spermatic cords supply nutrients and oxygen to the testes. Located along the urethra are accessory glands which are the Cowper’s gland, seminal vesicle and prostate glands. They produce slimy alkaline fluid which aids the movement of spermatozoa. This fluid together with the spermatozoa results in the formation of semen. The urethra is a uro-genital organ which helps to inject sperms into the vagina as well as the removal of urine. The urethra ends externally in penis.
Female Reproductive System: The female reproductive system (Fig. 3.4) includes the ovaries which produce the ovum or ova (eggs) enclosed by the graffian follicles and some hormones such as the oestrogen. A mature egg or ovum is released from the follicle in the ovary into the oviduct. This process is called ovulation.
As the ovum or egg is released from the ovary, the female animal comes into ‘heat’ and is willing to mate with the male animal.
Fertilisation, which is the fusion of the male sex cell (spermatozoa) and the female sex cell (egg or ovum) takes place in the fallopian tube or the oviduct. When the egg is fertilised by the spermatozoa, the fertilised egg anchors itself to the wall of the uterus. This process is called implantation. The development of the foetus takes place in the uterus. Below the uterus is the vagina which receives the spermatozoa during copulation. The female reproductive system terminates with an external opening called the vulva.
Development of the Embryo (Foetus): The fertilised egg is implanted in the uterus where the development of the embryo takes place. Soon, a number of embryonic membranes develop round the embryo. These are: the chorion, the allantois and the yolk sac. The amnion forms a sac in which the embryo lies and is filled with amnoitic fluid. Hence, the embryo is held in a liquid environment which acts as a buffer or “shock absorber”. This ensures the protection of the embryo. The allantois forms a sac which is excretory, respiratory and nutritive in function. It contributes to the formation of placenta. The yolk sac provides the food during the early stages of embryonic development. The chorion forms the outermost membrane, enveloping all these structures.
The placenta establishes an intimate connection between the embryo and the mother which aids nutritional, respiratory and excretory needs of the embryo (foetus). The placenta and the embryo are connected by the umbilical cord which develops from the allantois. The parental blood supply is linked to the foetal blood supply through this umbilical cord.
At the end of the gestation period (from fertilisation to birth), parturition (giving birth) takes place during which the young animal is pushed out through the vagina. The remainng part of the embryomic membrane known as after-birth is sent out after the birth of the foetus.
REPRODUCTIVE PROCESS IN POULTRY (Process of Egg formation in poultry)
The process of egg formation is controlled by hormones. The egg is formed partly in the ovary and partly in the oviduct
Ovary: The yolk is secreted by the ovary and enclosed in a follicle. The yolk increases in size by accumulating yolk materials carried from different parts of the body by the blood stream. The germinal disc is attached to the top of the yolk. The follicle bursts to release the yolk.
Infundibulum: The yolk released by the ovary is taken up by the infundibulum, the internal terminal part of the oviduct. Fertilization of the egg occurs in this part of the oviduct, before the other components are added. However, complete formation of the egg is independent of whether the egg is fertilized or not. The egg spends 15 minutes in the infundibulum before i moves to the magnum.
Magnum: In the magnum, the egg stays for three hours and part of the albumen is secreted on the yolk. Chalaza is also formed in this region. The egg now moves to the isthmus.
Isthmus: The egg stays here for 75 minutes and the two shell membranes are formed. The shape of the egg is also formed in this region after which it moves to the uterus.
Uterus: The egg stays here for 19-20 hours where the shell is formed from calcium carbonate secreted by glands of the uterus. Mineral solutions are also added to the egg after which it moves to the vagina.all
Vagina: The egg stays here for a very short time before it is laid through the cloaca or vent. It takes almost 26 hours for a complete egg to be formed and laid.
Structure of a Fertile Egg Shape: The egg (Fig. 3.6) is oval or oblong in shape. It is either brown or white in colour. The differences in colour are due to differences in breeds.
Shell: The hard shell covers the egg externally. It is rich in calcium carbonate and it protects the egg.
Membranes: Immediately after the outer shell are outer and inner membranes. Both membranes give protection to the egg.
Airspace: The airspace is located on one of the pointed ends of the egg. It is found in between the outer and inner membranes. The airspace is very important for respiration of the embryo.
Albumen: This is also called the egg white. It
accounts for over 50% of the total body weight of the egg. It is rich in protein.
Yolk: This is located at the centre of the egg. It is a yellowish jelly-like mass. It is rich in proteins, mineral salts, vitamins and other food substances. It supplies the embryo nutrients.
Embryo: This is also called germinal disc. This lis located at the centre of the yolk as a dark gspot. The germinal disc is only found in fertile eggs. It develops to form the chick during incubation period.
Chalaza: The chalaza extends to both sides of the yolk. It is a piece of thick protoplasm. It holds the yolk and the embryo in place within the albumen.
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