Egg Laying Hens
Understanding the
purpose of egg laying
hens
Why does the commercial
poultry industry exist?
Laying hens produce eggs for human consumption.
In 2009, per capita egg consumption in the US was 248
eggs per year.
What does that look like?
248 eggs
Equal to approximately 20.6 dozen
Trends in consumption
Consumption was down during the mid-twentieth century as
people moved from farms to cities.
Health concerns also decreased consumption mid- century.
In recent years, better health perceptions and the use of eggs
in fast food breakfasts have increased consumption to
present rates.
Where are eggs found?
Other egg containing foods...
Jelly beans
Crackers
Cookies
Pudding
Pretzels
Marshmallows
Pie crust
Cake
Tartar sauce
Frosting
Some candies
Most foods that have been battered and fried
Where in the country do
our eggs come from?
These are the largest egg producing states and they house
approximately 50% of the laying hens in the U.S.
In the U.S. approximately 3,136,500,000 dozen eggs
were produced during 2008.
There are over 60 egg producing companies with more
than 1 million laying hens, and 12 with more than 5
million.
In addition to producing eggs for the U.S., 21 million
dozen eggs were exported, mainly to Asian countries but
also to Europe, Canada, and Mexico.
Hen reproductive
physiology and egg
formation
An egg takes 23-27 hours to form and then be laid.
The shorter the time it takes the hen to form an egg,
the more days in a row a hen will lay an egg.
The number of days in a row that a hen lays an egg is
referred to as clutch size.
The term used for the parts of the hen where the egg
is created is oviduct.
Parts of the oviduct
Ovary
Infundibulum (Funnel)
Magnum
Isthmus
Uterus (Shell Gland)
Ovary
Hens only have one functional ovary (usually the left one).
The ovary contains a series of follicles that mature as yolk material
is added to them. Follicles look like little balloons on the ovary.
Yolk material is manufactured in the liver.
When one ruptures, ovulation occurs.
The ovulated follicle then leaves the ovary and makes its way down
the reproductive tract.
If two follicles rupture at the same time, double yolked eggs can form.
Ovary
Infundibulum (funnel)
After ovulation, the follicle enters the infundibulum also
known as the funnel.
The infundibulum is controlled by tactile (touch)
stimulation, so anytime something touches the inside of the
funnel, an egg forms.
This can lead to no yolk eggs or eggs formed around a piece
of the oviduct that has broken off in some cases
If the hens were allowed to breed, this is also where
conception would take place.
Magnum
This is where the thick egg white is formed.
Egg white is also called albumen.
Isthmus
The shell membranes form here.
The membranes are the thin, opaque films closest to the egg
shell when you break it open.
Uterus
The egg spends most of it time in the uterus (approximately
20 of the 24 hours).
The thin white (more liquid portion of the albumen) is
pumped into the egg through the membranes.
The shell forms. Most of the shell formation takes place at
night.
Even though the shell appears solid, there are actually
thousands of tiny pores in the shell that allow the developing
chick to breath while inside.
Uterus (continued)
The shell color is added.
A protective cuticle (wax like coating) is added.
The cuticle is like a natural sealant that prevents the
egg from losing moisture too quickly.
Other parts of the
reproductive tract
Vagina: Acts as a transport from the uterus to the
vent.
Cloaca: (Vestibule) Common chamber through which
the egg passes.
Vent: Outer opening of the hens reproductive and
digestive tracts. Eggs and the urine/feces mixture
eventually pass through the opening.
Q: How can you tell what
color egg a hen will lay?
Look at its ear lobe!
Blue ear lobes mean blue or blue green eggs.
Red ear lobes mean brown eggs.
White ear lobes mean white eggs.
Identify basic parts of an
egg
Yolk
The yellow part in the center of the egg.
The actual color of the egg yolk varies based on what the hen
who laid the egg is fed.
Hens fed a diet high in corn or alfalfa tend to have a more
dark yellow to orange colored yolk because those feeds are
high in a fat soluble pigment called xanthophyll.
Hens who are fed a diet of mostly wheat, which is low in
xanthophyll, would have a very light yellow or even
slightly grayish yolk.
Yolk (continued)
The yolk is separated from the white by the vitelline
membrane.
The yolk provides “food” that is essential for the developing
chick embryo.
Germ
The small white circle on the yolk.
In a fertile egg, this is where the embryo starts to
develop.
In non-fertile eggs, this spot stays small and white.
Albumen
Also called the egg white.
There are two types of albumen:
Thick albumen: Located closest to the yolk. The less
liquid, more dense portion of the white. In fresher eggs,
the thick albumen is denser than in older eggs.
Thin albumen: The more liquid “runny” portion of the egg
white.
Shell
The hard, normally white (may also be brown or greenish
blue) coating that provides the eggs solid structure and
shape and protects the developing embryo.
As mentioned before, the shell of an egg contains thousands
of tiny pores.
Shell membranes
Membranes that are located just inside the shell.
Act as a barrier between the shell and the albumen.
Air cell
The small open space at the large end of an egg.
Formed by the separation of the two shell membranes.
Provides the chick with an air supply during the final stage
of development just before hatching.
Older non-fertile eggs will have a larger air cell due to
moisture loss.
Chalaza
The small, white, rope-like structures at both ends of the
yolk.
These structures help keep the yolk centered within the egg.
If the yolk were to come into contact with the shell during
embryo development, the process would be aborted and the
embryo would cease development.
Systems for raising laying
hens
Floor house
Hens are raised on the floor of a light and temperature
controlled house.
Usually equipped with an automated feeding and watering
system, as well as a mechanical nest for egg gathering.
Hens are free to roam and congregate where they please.
Floor House
These are actually broiler chicks not
laying hens, but the house looks similar
at this stage of life.
Nipple Watering System
Standard equipment in a floor house
Automated feeder
Also standard equipment. Several designs
Cage house
Hens are raised in cages.
Sometimes there will be a single layer of cages per house.
Normally several rows of cages stacked on top of one
another (stacked deck house).
Cages have roll outs (areas to catch eggs) and normally an
automated egg gathering system.
Normally have an automated feeding and watering system.
Cage House
Two layers of cages are visible, but four
layers are present.
White Leghorns in a cage house
Note the feeder (metal trough).
Egg Roll Outs
Most are padded to prevent eggs from
breaking.
Egg Belt
Used to carry eggs to processing. Note the
padding on the near edge of the roll out.
Auger Feeder
Used to bring feed to birds.
Feeder
Egg belt/ roll out
The life cycle of a laying
hen
Laying hens usually have a two
year production cycle
Hens arrive at a grow out facility at one day of age.
Immature hens (pullets) usually stay in the grow out facility
for approximately 18 weeks. It is critical that during this
time pullets are not exposed to increasing day length.
Once hens have reached proper body weight, they can be
moved to the lay house. During this period hens should be
exposed to an increasing day length.
Types of eggs you can
buy at the grocery store
Brown Eggs
Just like regular white eggs, only brown.
Omega-3 Eggs
Eggs contain omega-3 fatty acid. Gives the eggs better
health perception. Eggs are usually more expensive.
Reduced cholesterol or cholesterol free eggs
Viewed as a heart-healthier alternative to
regular eggs.
Free-Range Eggs
Hens are required to be given some access to the
outdoors. Usually eggs are much more expensive.
Cage-Free Eggs
Hens are typically housed in floor houses with nest boxes.
No access to outdoors. Eggs are usually more expensive.
Organic Eggs
Hens must be fed a completely organic diet from hatching. Since
organic feed is expensive, eggs are more expensive.
Fertile Eggs
Laid by a hen who was given
the opportunity to mate.
Be sure to keep fertile eggs refrigerated or the embryo
could start to develop!
If that happens, what looks like a small black comma
will form on the yolk’s surface.
