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CHICKEN EGGS
The eggs you buy by the dozen at the market are very similar in
structure and function to all other bird eggs in the world. Inside
the hard shell are the yolk and the white. Several membranes keep
various parts of the system separated from each other and from
the environment. One additional structure in the egg is easily
overlooked—a tiny white mass hardly larger than the head
of a pin. This single cell, called the ovum, is the living part
of the egg. If the egg is laid by a hen that has not mated with
a cock, the ovum will not develop. If the egg is fertile, the
ovum will advance through a predictable sequence of dramatic changes
that will eventually result in the emergence of a new live bird.
The egg yolk is stored food for the developing embryo and fetus.
As the chick advances in size and complexity, the yolk is used
up until it is almost totally consumed at hatching time. The egg
white (albumen) is composed mostly of water with some dissolved
protein (albumin). The primary function of the white is to keep
the embryo moist and cushioned during the rigors of incubation.
A more detailed inquiry into the development of an egg and growth
of the embryo reveals still more structures and features, all
of which are exquisitely designed and complex in function. With
amazing frequency they produce the expected outcome—a new
chick.
Chickens are members of a clan of birds that have precocial chicks,
meaning that the chicks are up and running in a matter of hours,
covered with protective downy feathers, able to follow their mother,
and capable of feeding themselves. Birds like robins have altricial
chicks, meaning they are blind, naked, and helpless at the time
of hatching. They must be fed, kept warm, and defended against
predators, or they will perish. There are degrees of precocial
and altricial chicks; chickens have chicks that exhibit the highest
level of independence at hatching.
Chickens, like most birds, brood (sit on) their clutch of eggs
to ensure that they develop properly. If the eggs are not maintained
at 37°C (99°F) for 21 days, they will fail. Chickens lay
one egg a day. The hen will delay brooding her eggs until she
has accumulated her whole clutch of perhaps ten eggs. The first-laid
eggs stay alive but do not develop at the lower temperature. This
ensures that all the eggs will hatch at about the same time, a
tremendous advantage in the wild, where it is important to leave
the nest soon after the chicks have hatched.
In the classroom an incubator will substitute for the warm underside
of a hen. The eggs must be maintained at a constant temperature,
the humidity must be high, and the eggs must be turned at least
three times a day. If the eggs are not turned, the embryo will
usually adhere to the wall of the egg, and development will fail.
Commercial incubators provide for all these environmental needs.
Deciding to hatch chicks from eggs. Hatching eggs in your
classroom is a wonderful activity that you and students will long
remember. But there are several things to consider before doing
this investigation.
First, you need a source of fertile eggs. Supermarket eggs don't
deliver the goods. You can order fertile eggs from a biological
supply company, but eggs sent through the mail often get jostled
around too much and are not temperature-controlled, resulting
in poor hatching. Try to find a local supplier. Employees of feed
stores and pet stores may be able to direct you to a source for
fertilized eggs.
Second, you need to purchase the equipment—it does not come
in the kit. Delta Education carries all the equipment needed for
this investigation (1-800-258-1302). Check the Materials folio
for the ordering information. You can order an incubator, egg
turner, feeding tray, and water bottle. You will need to find
your own lamp and feed.
Third, you have to be prepared to give yourself over to the chickens
for 6 weeks—they demand time every day, including weekends
and holidays.
Finally, and perhaps most important, you need to have a place
for the chicks to go after they have spent a few weeks in class.
Consult a local feed store for advice.
We encourage you to plunge in and have a chicken adventure with
your class. The anticipation is palpable, the thrill of hearing
soft peeps inside the shells is unparalleled, and seeing the chicks
break out of the shells is magical. The soft peeping, the silly
antics, and the sense of something important going on that will
pervade your room will make for a memorable project. Do it—you'll
be glad you did.
Setting up the equipment. A reliable incubator is of utmost
importance for successful egg hatching. A still-air incubator
will do the job; circulated-air incubators generally cost quite
a bit more. Buy an incubator large enough to set at least a dozen
eggs. A large picture window in the top of the incubator is especially
nice, so a large number of students can gather around the incubator
at one time to watch them hatch.
Be sure the incubator you purchase has a thermostat so the temperature
will be closely regulated. Set the incubator up a few days before
you get your eggs to make sure that it is functioning properly.
It should maintain a temperature of 37°C (99°F), give
or take a degree, when the thermostat is operating. Usually a
screw on the incubator adjusts the temperature. Always read the
manufacturer's instructions that accompany the incubator you purchase
and follow them to the letter for best results.
It is essential to turn the eggs for successful hatching. If
you are turning the eggs manually, you will need to come back
to school on the weekends two or three times each day to turn
the eggs. Do not take the eggs home on the weekends; once they
are set they should not be moved. Automated egg turners are available.
They slowly rotate the eggs throughout the day and night, and
take care of the eggs on the weekends so you will not have to
return to school. They usually give a higher rate of hatching—70%
to 80%. The disadvantage is that students have less involvement
with the eggs. Hatching rate should be at least 50% if you turn
the eggs manually.
Eggs must incubate for 21 days. Eggs are rotated for the first
18 days, and lay still for the last 3 days. Perhaps the hen stops
turning the eggs when she hears the chicks begin to peep inside
the shell. When the eggs are resting during the final 3 days,
listen. A little hole or crack in the shell will be the first
indicator of hatching. The process may take a day or more. Be
patient. You may be tempted to help the chick cast off the shell,
but resist the urge. Rule one: Don’t touch the eggs during
the hatching process. The chicks have to do it all by themselves!
Once the chicks have hatched, they need a brooding pen, food,
and water. You can use a large cardboard box for a pen. The size
of the box depends on how many chicks you are raising. They need
plenty of room to grow. Put straw or sawdust in the bottom to
absorb droppings.
Provide a warm area in the pen, especially right after the chicks
hatch. Heat a large area of the pen with a lamp, but keep part
of the area cool for the chicks to exercise in. Buy an infrared
lamp if you are heating a large pen. A 100-watt bulb in a short
table lamp works fairly well in a smaller pen. Set up the pen
and measure the temperature in several locations to be sure it
is ready before the chicks hatch. The first week the chicks need
the temperature at 37°C (99°F); you can reduce the temperature
by 3°C (5°F) each week until it is down to 21°C (70°F).
Food and water should be available to the chicks at all times.
You may want to purchase a feeding tray designed to keep the chicks
out and the feed in. You can also purchase a water bottle with
a narrow tray that provides a constant supply of water. Chickens
can be very messy, so purchase special feeding equipment if you
do not want to be constantly cleaning the food and water containers.
Basic handling of eggs. Always make sure that hands are
clean before handling the eggs. The shell of the egg has many
pores that allow gases and moisture in and out. Dirty, oily hands
can block the pores and stop development of the chick.
If you want the eggs to start hatching on a Monday or Tuesday
when students are in class, you should set them on a Tuesday (3
weeks before you want them to hatch). If the eggs arrive on a
day other than Tuesday, keep them in a cool place—7°
to 15°C (45° to 60°F)—until you are ready to
put them in the incubator.
If you plan to turn the eggs yourself, use a pencil to mark each
egg with an X on one side and an O on the other side to be sure
you have turned all the eggs every time. The eggs should be placed
on their side with the small end pointed slightly down. As the
chick develops inside the egg, its head will be at the large end
of the egg. If the large end is down and the developing chick
is standing on its head, it will die. The eggs need to be turned
three times a day through the 18th day. The last 3 days the eggs
should not be turned.
If you are using an automatic turner, follow the manufacturer's
instructions for installing it in the incubator. Be sure to place
the eggs in the turner with the small end pointed down. Take the
turner out of the incubator at the end of the 18th day. The eggs
no longer need to be turned, and taking out the turner will prevent
injury to the newly hatched chicks.
The amount of moisture in an incubator is also critical for a
good hatch. Most incubators have a trough to keep filled with
water to ensure enough moisture. If the incubator has vent holes,
keep them plugged for the first few days. After that open the
small vents to allow air circulation through the incubator. Monitor
and correct (if necessary) the temperature throughout the whole
process.
Basic care of chicks. The class may be able to focus on
little else as the eggs begin to hatch. This will be a very exciting
time! The chicks should stay in the incubator until they are completely
dry and fluffy. It is also important to maintain a steady temperature
in the incubator as the chicks hatch, so remove chicks to the
brood pen only once a day. The newly hatched chicks will be tired
from the hard work of breaking through the shell and probably
won't eat for the first 24 hours.
Chicks instinctively begin pecking shortly after they hatch.
Be prepared for some curious chick behaviors. For example, the
first few days the chicks will be very active one moment, then
fall in a heap with their heads on the ground as if they were
taking their very last breath. A few moments later they'll be
up and chirping once again.
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