makes it hard. It protects the interior parts of the egg and has pores that allow
gaseous exchange.
Shell Membranes
This is the inner lining of the shell. It has 2 membranes that separate at the broad
end of the egg to form an air space.
Albumen (egg white)
The albumen makes up 55% of the egg. It is a jelly-like, colourless fluid when
fresh.
It surrounds the yolk and serves as a food reserve for the developing chick.
Chalazae
These are 2 twisted cords which hold the yolk from both ends of the egg.
If the chalazae is broken the yolk shakes and is displaced from its normal position.
Yolk
The yolk makes up 33% of the egg. It is yellow in colour and spherical in shape. It
has a germ spot which develops into a chick. A fertilized germ spot is called a
plastoderm while an unfertilized one is called a plastodisa. The yolk contains
food reserves for the developing chick and is rich in vitamins, fats, minerals and
protein.
Qualities of Eggs for Incubation
Eggs for incubation should have the following qualities:
They should be fertilized
They should be of medium size i.e. about 55-60gms in weight
Should have smooth shells
Oval shaped
Not cracked
Clean to ensure that pores are open
Shell
Chalazae (dense protoplasm)
Inner
membrane
York
Air space
Germ layer spot
Outer membrane
Albumen
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Should not have abnormalities such as blood spots, meat spots, double yolk
etc.
Should not be more than 5 days old.
Egg Candling
Egg candling is a method used to check eggs for fertility and determine which ones
will hatch into chicks. It involves observing an egg through light rays, see figure 3.7
for the candling technique.
Figure 3.7: Candling technique
Candling Method
As you can see from Figure 3.7, candling is a simple method which you can do at
home using the following procedure:
Cut a small round hole on top of a cardboard box. The hole should be just
big enough to sit the pointed end of the egg
Place a torch inside the cardboard box just under the hole
Place the egg on the hole and turn on the light
You will be able to see if the egg is fertile. A fertile egg has blood veins and a
black spot inside the egg. Figure 3.8 shows you the results of candling.
a) Fertilised egg b) Unfertilised egg
Egg
Light source
Hole to place egg
Cardboard or
wooden box
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Figure 3.8: Results of candling
Incubated eggs should be candled 2 or more times. The first candling should be done on the 5th and 7th day to check for fertility. If they are fertile blood veins will be seen. If they are not, they appear clear. The second candling is done on the 18th day to confirm the presence of a chick. An egg with a living embryo clearly shows a large section containing the embryo and a smaller clear section, containing the air space.
Methods of Incubation
Egg incubation means putting an egg in a place where the right conditions for embryonic development are provided so that a chick is ultimately hatched from the egg. For chicken eggs, these conditions must be provided for 21 days.
How are incubation eggs selected?
Eggs for incubation are selected on the following basis:
Eggs that;
Are fertilized
is neither too small nor too large
are clean
have no cracks on the eggshell
are less than seven (7) days
are from breeder birds with a good cock-hen ratio.
are stored under low temperature below 23.90C.
There are two main methods of incubation. These are:
Natural incubation
Artificial incubation
Let us briefly look at each method starting with the natural incubation.
A. Natural Incubation
In natural incubation, you choose a broody hen that is large enough to cover the eggs and thus keep them warm. The hen should be healthy and preferably vaccinated, with a good brooding and mothering record. The signs of broodiness are indicated when the hen stops laying, remains sitting on her eggs, ruffles her feathers, spreads her wings and makes a distinctive clucking sound. Brooding may be induced with dummy eggs.
About 10-15 eggs are adequate to sit on. More than 15 eggs leads to low hatchability. Allow the hen to sit in a dark, vermin proof, simple laying box or quiet place for the 21 days. Use nesting material, such as, dry grass, sawdust and wood shavings to line the nest. The hen warms the eggs and turns them regularly to ensure even heating until they hatch. Figure 3.9 below shows an illustration of brooding hens.
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Figure 3.9: Brooding hens
Factors to consider during natural incubation
You should consider the following factors during natural incubation:
The broody hen should be dusted with appropriate insecticides to rid her of parasites itchy parasites often cause hens to get up and abandon eggs;
Provide dry grains with grit, greens and water for the brooding hen;
Remove any broken eggs;
Wash eggs that get soiled (dirty) using a clean cloth soaked in warm water;
Ensure no egg is left out in the cold by providing less than 15 eggs per hen;
After the eggs hatch, you should move mother and chicks to a new clean place.
Advantages of Natural Incubation
The natural incubation method has the following advantages:
A small-scale farmer who cannot afford an incubator can multiply his flock using this method;
It is less laborious as there is no need of turning the eggs and checking the temperature;
It does not require maintenance cost;
It requires little skill.
Disadvantages
Natural incubation has a number of disadvantages. These are:
Only a few chicks can be hatched at a time per hen;
The farmer cannot plan when to incubate;
The availability of broody hen sitters is not always possible.
B. Artificial Incubation
There are many commercial artificial incubators of varying capacities. Most depend on electricity, but some use gas or kerosene for heating. All use a thermostatic switching device to keep the temperature constant within one (1) Celsius degree. The correct humidity is usually maintained by having a pr
