This document provides an overview of avian reproductive systems and egg formation in chickens. It describes the female reproductive system including the ovary and oviduct. The male reproductive system is also summarized. The process of egg formation is then outlined, beginning with ovulation and continuing through albumen, shell, and membrane formation in the oviduct over 25-26 hours. Key structures of the finished egg like the yolk, chalazae, and shell are defined. Differences between fertile and infertile eggs are highlighted. Finally, the concept of egg clutches is introduced.

1. Eggcellent!!!!
Dr.Gurram. Srinivas,
Assistant Professor
Department of Poultry Science,
College of Veterinary Science
Korutla, Karimnagar, 505326
Telangana, India

2. Lecture out line
•Male & female reproductive
system
•Egg structure
•Egg formation

3. FEMALE REPRODUCTIVE SYSTEM
 Birds are unique among animals as they reproduce
through an egg .
 Two parts
1)Ovary
2)Oviduct
 At the time of early embryonic development, two
ovaries and two oviducts are present.
 left pair (ovary and oviduct) develops and
functional in all species of birds
 Kiwis - both the left and right ovaries develop and
only the left oviduct develops

4. Female Reproductive System:
Ovary
• Mature ovary consists of
numerous developing
follicles
– Appears like a
cluster of grapes

5. Ovary
 The left ovary is situated at dorsal part of abdominal
cavity and the fore end of kidneys
 is attached to the abdominal cavity wall by the meso-
ovarian ligament
 ovary is a cluster of developing yolks or ova
 At hatch, pullet chicks have tens of thousands of
potential eggs. Most of these, however, never develop
to the point of ovulation.
 Each ovum surrounded by a vitelline membrane. As
the ovum develops, yolk is added.

6.  The color of the yolk comes from fat soluble pigments
called xanthophylls contained in the hen’s diet.
 Hens fed diets with yellow maize, or allowed to range
on grass, typically have dark yellow yolks.
 Hens fed diets with white maize, sorghum, millet or
wheat typically have pale yolks.
 The color of the yolks improved by marigold petals
(xanthophylls ).

7. Ovary/yolk
 The liberation of ovum from graffian follicle is called
Ovulation
 Ovulation occurs normally 14 to 75 minutes after
oviposition (the laying of the fully formed egg).
 yolk size in the egg - up to 40 millimetres in diameter .
 on the distal surface of mature follicle have a elongated
area which is free of blood vessels called as stigma, is
where the follicle normally splits to release the yolk
into the oviduct.
 If the follicle splits at other than the stigma, the
numerous blood vessels will rupture and result in
blood spot in egg.

8.  Occasionally the vitelline membrane is damaged and
pale spots develop on the yolk called as mottling
 A high incidence of yolk mottling
 use of Nicarbazin & Piperazine and dibutylin
dialaurate
 cottonseed meal (gossypol) and sorghum (tannin)
 A calcium deficient diet.

9. Photograph of the ovary of female
chicken, indicating the location of the
stigma on an ovum
stigma

10. Blood spot in yolk

11.  Meat spots in egg white.
 They are formed when small pieces of the wall of the
oviduct are sloughed off when the egg is passing
through oviduct (candling)

12. Female reproductive system

13. oviduct
 The oviduct is a long zig zag tube (25-27 inches long)
consisting of glandular and muscular parts .
 Oviduct extends from the ovary to the cloaca.
 It has 5 distinct parts, viz.
1) infundibulum (9cm),
2) magnum (33cm),
3)isthmus (10cm),
4)uterus (10-12cm)/shell gland
5)vagina (12cm)

14. S.No Part Length Time spent Function
1 Infundibulum 9 cm 18 mins 1)Engulfs yolk
2)Reservoir for
spermatozoa, 3)Fertilization
2 Magnum 33 cm
(largest
portion)
2 hr 54 mins Thick white or albumen (40
%) added
3 Isthmus 10 cm 1 hr 15 mins Some albumen and inner
and outer shell membranes
are added
4 Uterus/shell
gland
10-12 cm 20 hrs 40 mins Shell (CaCo3) over the egg
(47%calcium from her
bones), pigment deposition
(Porphrin- brown color)
5 Vagina
(Muscular
portion)
12 cm Cuticle is added,
helps in expelling the egg
during oviposition
Total 74 cm 25-26 hours

15. Male reproductive system
Testis
Vas difference
Cloaca
Copulatory
organ

16.  include pair testes, vas deferens, cloaca and the
rudimentary copulatory organ.
 do not have a penis.
 The testes are bean shaped bodies located against the
backbone at the front of the kidney.
 Their size is not constant and they become larger when
the birds are actively mating.
 The left testes are often larger than the right.
 Epididymis in birds is smaller than in mammals

17.  The testis is formed of numerous slender seminiferous
tubules, inside which spermatogenesis takes place.
From each tubule arises the vas deferens, which join
together to form the long coiled epididymis.
 The epididymis of each side continues down as the vas
deferens and terminates in the cloaca
 The vas diferens transports the sperm.

18.  On the median ventral portion of the cloaca is a small
button-like structure called copulatory papilla, which
is the rudimentary copulatory organ
 During copulation the papilla of male and female are
everted and pressed together so that sperms are
ejected directly into the female reproductive sytem
 In healthy cocks, semen volume 0.3-1ml.contains on
average 3-5 million sperm per cubic millimeter.
 The pH of the semen - 7.45 to 7.63.
 androgens that influence the secondary sex
characteristics such as comb growth and male
behaviour and mating.

19. FERTILIZATION
 On the surface of yolk there is a tiny, whitish spot
called the blastodisc.
 This contains a single female cell. When a yolk enters
the infudibulum, a sperm penetrates the blastodisc
and fertilizing occur. The blastodisc becomes a
blastoderm.
 The hen will continue to lay eggs even if she is not
fertilized by the rooster.

20. Sperm Cell Storage
• A biological necessity
to produce fertile
eggs in the avian
system

21. Fertilization
• Location -
Infundibulum
• Time - within
~ 5 minutes
following
ovulation or
before the
ovum enters
the magnum

22. Fertilization
• Shell formation takes
24-26 hours to
complete
• Hen’s body
temperature 104 -
106o F

23. ROOSTER
mature male
chicken

24. PROCESS OF EGG FORMATION
 The yolk is not the true reproductive cell
 When the female attains sexual maturity (FSH)-
mature ovum inside the graffian follicle grows rapidly.
 The yolk weight also increases 7 days prior to ovulation
due to the deposition of yolk material over the ovum in
(alternate layers of white and yellow)
 white layer -night time
 yellow layer - day time
 due to the deposition of yolk, the nucleus migrates
from the centre of the ovum to the periphery and lies
underneath the vitelline membrane

25.  The nucleus of the infertile egg is called 'germ
spot' and that of fertile egg 'germ disc'
 The anterior pituitary - FSH - that regulates the
growth and maturity of graffian follicle
 Luteinising hormone (LH) that helps to release
the ovum by rupture of graffian follicle
 Ovulation
 oviposition (laying of egg)
 In emu for egg formation – 72 hours (3days – one
egg)

26.  Albumin - Magnum
 Inner and outer shell membranes & water – Isthmus
 Egg shell (CaCo3)and cuticle – uterus/shell gland
 The tubular and unicellular glands present in uterus
which secrete a watery fluid and added to the
albumen through the shell membranes
 5 hours before the oviposition shell pigments are
added.(brown colour –Porphyrin)
 laying of egg, is through the contraction of uterus.
 oxytocin and vasotocin responsible for uterine
contraction and Oviposition.

27. Four Major structures from outside to inside are
Shell
Shell membranes
Albumen
Yolk

29. EGG SHELL
 Cuticle
 Spongy or calcarious layer
 Mammillary layer or matrix and pores
 Microscopic Pores- 8,000-10000 per egg, distributed
unevenly over the shell surface (more at broad end
than narrow end).
 Exchange of volatile compounds between the shell
membrane and cuticle.
 CaCo3

30. SHELL MEMBRANE
 Air cell
 Outer shell membrane
 Inner shell membrane
 Air cell is situated in between the two membranes at the
broad end
 Air cell - formed as a result of contraction of the egg
contents, soon after oviposition, due to differences in the
temperatures exposed to by the egg prior to and after
oviposition
 The outer shell membrane is attached to the shell.
 The inner shell membrane closely surrounds the albumen

31. ALBUMEN
 consists of 4 layers
 Chalaziferous or inner thick white, which forms (3%)
 Inner thin albumen (17%)
 Outer thick firm or dense albumen (57%)
 Outer thin albumen (23%) of total albumen
 The chalaziferous layer -very close to the yolk
immediately surrounding the vitelline membrane
of the yolk –
 This layer twists into two chords on either sides of
the yolk called chalazae, which are formed due to
rotational movement of the egg in the oviduct

32. Functions of chalazae
 Chalazae - hold the yolk central position and thus
serves as an anchor for yolk
 Chalazae - contain a protein called lysozyme, which
is possessing antimicrobial properties and helps to
prevent the microbial spoilage of the egg
 Ageing, improper storage and microbial
spoilage makes thick albumen watery

33. YOLK
 Latebra is the centre of the yolk, which is a small,
nearly circular core of light coloured fluid, which does
not completely harden on boiling
 Nucleus of Pander is a cup-shaped structure, which is
an extension of the neck of latebra, connecting the
base of the germinal disc
 Germinal disc located on the surface of yolk, from here
Embryo formation begins.
 "Vitelline membrane" is a semi-permeable elastic
membrane, surrounding the yolk, separating the yolk
material from the albumen

34. Fertile and Infertile Eggs
Infertile egg Fertile egg

35.  In an infertile egg it is unicellular (ovum) and contains
haploid number of chromosomes, called
"Blastodisc". It is circular in shape, with a diameter of
about 3.5 mm and with vacuoles in it.
 Where as in a fertile egg, it is a multicellular structure
having diploid number of chromosomes, called
"Blastoderm". It is oval in shape, with an average
diameter of about 4.5 mm and with no vacuoles in
it.

36. Clutches
 Birds lay eggs in clutches
 Eggs laid on successive days are called a clutch.
 Clutch size is an individual characteristic and may vary
from 2 up to 100 eggs.
 However, the normal clutch size is from 3-8 eggs.
 The larger the clutch size – good layers
 Small clutch size indicates an inferior layer.

37.  ovulation usually occurs in the morning and almost never
after 3:00 PM.
 Ovulation of a yolk for the next egg in a clutch occurs
within an hour of laying the previous egg.
 and so that each day the hen gets later and later in her
timing.
 Since hens do not typically ovulate after 3:00 PM, the next
ovulation is delayed until at least the next day and egg
laying is interrupted.
 This delay results in the break between clutches and the
cycle repeats itself a day or so later. PHUSE

38. double-yolked eggs
 This phenomenon can be related to hen age but
genetic factors are also involved.
 Young hens sometimes release two follicles from the
ovary in quick succession.

39. Egg structure

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44. Eggcellent!!!!