The Avian EggStructure, 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 EggSeven Components

• Yolk• Albumin• Membranes• Chelazia• Chorioallantoic

Membrane• Air Cell• Shell

Anatomy of the EggSeven 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

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 Most female birds have one functionally ovary (on the left)

• 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

– Regulates rate of development– Tolerance for lowered temperature decreases as

embryo grows– The incubation period (from laying to hatching) for

budgie and cockatiel eggs is 18 to 21 days, respectively, whereas for the African grey parrots, Amazon parrots, and macaws it is app. 26 days

• Humidity: regulates water loss– Determined by internal egg temp (humidity is 100%)

and ambient humidity and gradient between the two

• Turning

Incubation Times

Species Time to Pip (d) Time to Hatch(h)

Chicken 20.5 6 – 12Cockatiel 21 24-48SC Cockatoo 28 24-28Peregrine 29 36Bald Eagle 34 24-30PhilippineEagle

56 30-45

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:– 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

• 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

• Unretracted Yolk Sacs• Idiopathic

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

Malpositions and Hatching Problems

• Oversized Embryos

Dystocias (Egg-Binding) and Other Problems

Internal Laying