The Avian Egg Structure, Production, Function

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

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

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)

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

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

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

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

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

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

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

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

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

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

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

Cloacal Structure Oviduct

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: 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

Incubation Times

Humidity and Shell Conductance

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

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

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

Appearance of Fertile Egg at Lay and during Early Development

Stages of Embryonic Development

Stages of Embryonic Development

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

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

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

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.

Appearance of Healthy Chick at Hatch Color Hydration Status

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

Malpositions and Hatching Problems Unretracted Yolk Sacs Idiopathic

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

Malpositions and Hatching Problems Oversized Embryos

Dystocias (Egg-Binding) and Other Problems Internal Laying

Radiographic Appearance of Egg-bound Cockatiel

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

Management of Dystocias Lubricate and Apply Pressure Crush and remove fragments

Management of Dystocias

Management of Dystocias Impaction in Oviduct

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

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

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.