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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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