1. The Avian Egg Structure, Production, Function

2. Topics Anatomy of the Egg Anatomy of Avian Female Reproductive Tract
Process of Egg Formation
Aspects of Incubation and Hatching
Dystocias

3. Egg Types Eight Basic Shapes
Egg sizes range from 10 mm to 145 mm in length

4. Egg Colors
Multitude of colors, but all formed from two pigments derived from porphyrins
Color and mottling serves to camouflage the eggs in the nest
Cavity nesting birds have colorless eggs
Colors are added in the uterus during shell formation (below)

5. Anatomy of the Egg Seven Components
Yolk
Albumin
Membranes
Chelazia
Chorioallantoic Membrane
Air Cell
Shell

6. Anatomy of the Egg Seven Components
Yolk
Albumin
Membranes
Chelazia
Chorioallantoic Membrane
Air Cell
Shell

7. Yolk Formed in the liver, transported to ovarian follicle 33% lipid
19% protein
48% water
Layed in concentric layers

8. Albumin Four distinct layers Chalaziferous - inner thick
Inner thin layer
Outer thick layer
Outer thin layer
Protects yolk from invasion by microorganisms and provides water, protein and minerals to the embryo

10. Proteins found in Albumin
Ovalbumin (54%): source of amino acids
Ovotransferrin (13%): iron chelator -- prevents bacterial growth
Ovomucoid, ovoglobulins, avidin comprise the remainder
Avidin is a biotin inhibitor - reduces bacterial growth

11. Chelaziae Twisted fiber-like structures at each pole
Hold yolk in place inside the egg
permit limited rotation
inhibit lateral displacement

12. Shell Membranes Inner and Outer Membranes Envelope yolk and albumin
Contiguous with each other except at one end where they separate to form air cell
Mammilary cores are embedded in the outer membrane -- initial site of calcification

13. Shell Matrix Organic mucopolysaccharide matrix
Becomes calcified to form hard outer shell
Hens egg weighs grams at time of lay
2.5 grams of calcium in the egg
A hen laying 280 eggs per year transports 30 times the calcium content of her entire body for shell formation
Cuticle: waxy layer with pigments

14. Cross-section of Egg Shell
Membranes
Pores
Gas Exchange
Oxygen
Carbon Dioxide
15% weight loss during incubation
Related to incubation time (see tables)

15. Female Reproductive Tract
Ovary
Infundibulum - site of fertilization
Magnum - albumin addition
Isthmus - membranes
Uterus - shell gland
Vagina - transport to exterior
Sperm storage occurs at various sites in tract in some species

16. Female Reproductive Tract
Ovary
Infundibulum - site of fertilization
Magnum - albumin addition
Isthmus - membranes
Uterus - shell gland
Vagina - transport to exterior
Sperm storage occurs at various sites in tract in some species

17. Cloacal Structure
Oviduct

18. Incubation Issues Temperature Humidity: regulates water loss Turning
Regulates rate of development
Tolerance for lowered temperature decreases as embryo grows
Less tolerance for increase temps: C is lethal for more than min depending on stage of embryo development
Humidity: regulates water loss
Determined by internal egg temp (humidity is 100%) and ambient humidity and gradient between the two
Turning

19. Incubation Times

20. Humidity and Shell Conductance

21. Incubation Issues Turning Most critical from day 3 to day 7
Required for:
Proper incorporation of albumin into amnion
Failure to incorporate leads to water loss from albumin, increased viscosity and setttling between chorioallantoic membrane and inner shell membrane
This results in decreased oxygen diffusion
Ideal turning rate:
Minimum of 3x/d
More than 24x/d is not necessary

22. Managing Water Loss by the 14 -16 % Principle
Weigh egg at time of lay
Calculate projected weight at hatch by subtracting 15-18% of weight
Plot laid weight on day 1; and pip weight at appropriate point for incubation time (e.g. 21 days)
Connect with a straight line
Weigh eggs periodically during incubation

23. Altering Weight Loss Too much loss: Too little loss:
Place in incubator with higher humidity
Cover part of the egg with white glue
Too little loss:
Place in incubator with lower humidity
Thin part of the egg-shell by sandpapering

24. Appearance of Fertile Egg at Lay and during Early Development

25. Stages of Embryonic Development

26. Stages of Embryonic Development

27. Assessing Eggs during Incubation: Candling
Blood Vessels of Chorioallantoic layer
Embryonic Position

28. Assessing Eggs during Incubation: Candling
Blood Vessels of Chorioallantoic layer
Embryonic Position and Condition

29. Assessing Eggs during Incubation: Radiology
Embryonic Position and Condition
Note head down position

30. Hatching Process Membrane Drawdown - due to water-loss
Air Cell Formation - initiation of air-breathing by developing chick
Pipping
Rotation - counterclock-wise
Assisted Hatching - do not initiate until chorioallantoic blood vessels shut down.

31. Appearance of Healthy Chick at Hatch
Color
Hydration Status

32. Malpositions and Hatching Problems
Head at small end of egg is most common (mp2) - reduced hatchability
Head under left wing (mp 3) - lethal
Oversize Embryos
Unretracted Yolk Sacs

33. Malpositions and Hatching Problems
Unretracted Yolk Sacs
Idiopathic

34. Malpositions and Hatching Problems
Head at small end of egg is most common (mp2) - reduced hatchability
Head under left wing (mp 3) - lethal

35. Malpositions and Hatching Problems
Oversized Embryos

36. Dystocias (Egg-Binding) and Other Problems
Internal Laying

37. Radiographic Appearance of Egg-bound Cockatiel

38. Management of Dystocias
Correct dehydration
Provide Warmth
Correct Calcium Depletion
Prostaglandin application to cloaca
Forced expulsion/removal

39. Management of Dystocias
Lubricate and Apply Pressure
Crush and remove fragments

40. Management of Dystocias

41. Management of Dystocias
Impaction in Oviduct

42. Management of Chronic Egg-Laying
Photoperiod Control
Removal of stimuli
Chemical
Lupron
HCG
Surgical

43. Summary
Egg is self-contained external development encasement for embryo
Formation and laying is a significant physiological and metabolic factor for the hen
Embryonic development can be monitored through the egg shell
There are six classical malpositions

44. Summary
Hatching can be assisted after draw-down of chorioallantoic membranes
Dystocias can be treated through a variety of removal techniques
Chronic egg-laying is a significant problem for owners of some birds; management methods vary.