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The Avian Egg Structure, Production, Function

Explore the structure, formation, and functions of avian eggs. Delve into egg anatomy, female reproductive tract, incubation, and hatching processes. Learn about different egg types, sizes, colors, and components like yolk, albumin, membranes, chalazae, and shell. Discover how eggs develop, the role of proteins, chelaziae functions, shell matrix, and incubation challenges like temperature, humidity, and turning. Manage water loss, alter weight loss, and assess eggs during incubation using candling and radiology techniques. Understand stages of embryonic development and the hatching process.

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The Avian Egg Structure, Production, Function

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  1. The Avian EggStructure, 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 EggSeven Components • Yolk • Albumin • Membranes • Chelazia • Chorioallantoic Membrane • Air Cell • Shell

  6. Anatomy of the EggSeven 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

  9. 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

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

  11. 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

  12. Shell Matrix • Organic mucopolysaccharide matrix • Becomes calcified to form hard outer shell • Hens egg weighs 50 - 60 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

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

  14. 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

  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. Cloacal Structure Oviduct

  17. Incubation Issues • Temperature • Regulates rate of development • Tolerance for lowered temperature decreases as embryo grows • Less tolerance for increase temps: 46-47 C is lethal for more than 60-90 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

  18. Incubation Times

  19. Humidity and Shell Conductance

  20. 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

  21. 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

  22. Altering Weight Loss • Too much 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

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

  24. Stages of Embryonic Development

  25. Stages of Embryonic Development

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

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

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

  29. 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.

  30. Color Hydration Status Appearance of Healthy Chick at Hatch

  31. Malpositions 1 - 6 Head at small end of egg is most common (mp2) - reduced hatchability Head under left wing (mp 3) - lethal Oversize Embryos Unretracted Yolk Sacs Malpositions and Hatching Problems

  32. Malpositions and Hatching Problems • Unretracted Yolk Sacs • Idiopathic

  33. Malpositions and Hatching Problems • Malpositions 1 - 6 • Head at small end of egg is most common (mp2) - reduced hatchability • Head under left wing (mp 3) - lethal

  34. Malpositions and Hatching Problems • Oversized Embryos

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

  36. Radiographic Appearance of Egg-bound Cockatiel

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

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

  39. Management of Dystocias

  40. Management of Dystocias Impaction in Oviduct

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

  42. 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

  43. 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.

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