Transcript The Avian Egg Structure, Production, Function

The Avian Egg
Structure, Production, Function
By
Akrum Hamdy
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
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•
•
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
– 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
Species
Chicken
Cockatiel
SC Cockatoo
Peregrine
Bald Eagle
Philippine
Eagle
Time to Pip (d)
Time to Hatch(h)
20.5
21
28
29
34
56
6 – 12
24-48
24-28
36
24-30
30-45
Humidity and Shell Conductance
Species
Temp ©
Pied-Billed
Grebe
30 – 32
Humidty
%
>95%
GH2O
Chicken
30 – 32
60 – 70% Intermediate
Ostrich
30 – 32
20%
High
Low
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 airbreathing 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
Radiographic Appearance of
Egg-bound Cockatiel
Management of Dystocias
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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.