Egg formation

egg structure and formation

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

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 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 - 106 o 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. EGG STRUCTURE   Four Major structures from outside to inside are Shell Shell membranes Albumen  Yolk Shell Shell membranes Albumen  Yolk

28. 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

29. 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

30. 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

31. 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

32. 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

33. Fertile and Infertile Eggs Infertile egg Fertile egg

34. 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.

35. 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.

36. 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

37. 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.

38. Egg structure

39. THANK YOU

40. Eggcellent !!!!