Avian Production Management

PROCESS OF EGG FORMATION

Formation of egg (Click here to view the animation for egg formation)

• The yolk is not the true reproductive cell, but a source of food material from which the live cell (blastoderm) and its resultant embryo partially receives its nutrients for growth
• When the female attains sexual maturity- mature ovum inside the graffian follicle grows rapidly and reaches its full size in about 9 to 10 days due to the action of Follicle Stimulating Hormone (FSH) produced by the anterior pituitary
• The yolk weight also increases 7 days prior to ovulation due to the deposition of yolk material over the ovum in concentric and alternate layers of white and yellow of which, white layer of yolk is deposited during the night and the yellow layer during the day
• As the ovum increases in size, due to the deposition of yolk, the nucleus migrates from the centre of the ovum to the periphery and lies underneath the vitelline membrane
• The nucleus of the infertile egg is called 'germ spot' and that of fertile egg 'germ disc'
•  The anterior pituitary releases Follicle-Stimulating Hormone (FSH) that regulates the growth and maturity of graffian follicle and Luteinising hormone (LH) that helps to release the ovum by rupture of graffian follicle
• The liberation of ovum from graffian follicle is called Ovulation
• Ovulation occurs normally 14 to 75 minutes after oviposition (act of laying) 
• Most of the albumen is formed in the magnum, so it is known as the albumen-secreting region of the oviduct. Peristaltic movement of the magnum pushes the ovum to the isthmus
• Chalazae, the egg protein formed in the magnum, becomes visible only in the uterus and not before, probably because of change in colloidal structure of albumen adjacent to the yolk and rotation of this albumen around the yolk in the uterus.
• The inner and outer shell membranes of the egg are formed in the isthmus. Probably some amount of water is also added to albumen in the isthmus.
• The uterus is responsible for the formation of egg shell and hence is also known as shell gland. Calcium required for the formation of the egg shell is mobilized from the feed assimilated and long medullary bones.
• The tubular and unicellular glands present in uterus secrete a watery fluid which is added to the albumen through the shell membranes.
• The shell pigments are formed in the uterus during the last 5 hours before the oviposition and brown colour of egg shell is due to the pigment Porphyrin.
• The cuticle is laid on the outside of shell in the uterus and it represents the last of the concentric layers of egg formation.
• The oviposition or laying of egg, is through the contraction of uterus. The hormones responsible for uterine contraction and oviposition are oxytocin and vasotocin released from the posterior lobe of pituitary.