Exotic Newcastle Disease - Details from California Dept. of Food and Agriculture web site
Quail Embryo Series
James C. Hermes, Ph.D.
Extension Poultry Specialist and Associate Professor of Animal Sciences, Department of Animal Sciences, Oregon State University
This page is designed to be used with the Quail Hatching in the Classroom program through Poultry Extension, at Oregon State University. The information presented here is to supplement the educational opportunities for teachers that are using the incubators and hatching eggs supplied through this program.
(To view the pictures that accompany the text, click on the Picture number.)
What are eggs for? (Most children will say that they are to eat). Yes indeed, eggs are known as an excellent food source. In fact, eggs are one of Nature's most perfect foods. They contain nearly everything that we need to grow and be healthy. They contain protein, carbohydrates, fats, minerals and vitamins. The protein in eggs is the highest quality protein of any of the foods that we eat. However, there are two nutrients that we need that are not found in the eggs that we eat.
Calcium is one of the nutrients that is not found in the part of the egg that we normally eat. (We could get calcium if we were to eat the eggshell.) The other missing nutrient is vitamin C. Why do you think that eggs don't have vitamin C? The reason is that the baby chick doesn't need vitamin C. In fact, eggs are such a good food source they can almost be considered BABY FOOD!!! If you consider the real reason that eggs are produced, calling them baby food is really not so far off. The contents of the egg are really to provide the nourishment of the developing baby chick in the egg before it hatches.
To fully understand eggs a little better and where the chick comes from we need to start at the beginning. First, where do eggs come from?
The egg has its beginning deep inside the body of the hen. There are two separate organs which are involved in making the egg. The ovary (the yellow organ at the top of the picture) produces the ovum (or yolk). It is the ovum which will eventually become the chick. As you can see in the picture, the sizes of the yolks are from very small to quite large. The yolks increase in size over the course of about 10 to 12 days. The largest of the yolks will be released in to the body of the bird during ovulation. (This process is the same in all birds, however the differences between species are in timing. Some birds lay an egg nearly every day while others lay only occasionally). Once released, the yolk is ready to become part of the completed egg.
The other organ involved with making the egg is the oviduct. This is the other structure in the picture. In fact, the name of this structure is very descriptive. Ova means egg and duct means tube, so we put the name together and we get a tube that makes eggs.
The first part of the oviduct, the red part, is called the infundibulum (funnel). This part of the oviduct actually grasps the yolk and engulfs it to begin it journey to becoming a fully formed egg. It is here that the ovum is fertilized to begin its development into the chick. The egg only remains in the infundibulum for about 15 minutes.
After fertilization the egg continues down the oviduct and into the magnum (the purple part of the tube). Here the albumen (egg white) is added around the yolk. This process takes about 3 hours. The egg then enters the isthmus (the orange part). Here two membranes are formed around the egg white. These membranes serve many purposes but in this case they help to maintain the shape of the egg while the shell is being formed and the provide a base for the shell to stick to. The egg remains in the isthmus for about 1.5 hours.
Next, the egg moves into the shell gland (the green part). The shell gland is sometimes call the uterus. It is here that the shell is put on. As the shell is being formed the egg is turning in the gland so that the egg shell is smooth and ovoid. If the egg is to be colored, as in the Japanese quail, the color is added right at the end of the time that the egg is in the shell gland. The blue or green color in chicken eggs is found throughout the shell. The process of shell formation takes about 20 hours to accomplish.
The time it takes for the whole process to occur from the time the ovum (yolk) is released from the ovary until the egg is laid is about 24 to 25 hours.
One thing to remember, the eggs you buy at the grocery store will not develop into a chick. These eggs are produced in the absence of the rooster so fertilization is not possible.
If you could cut a fresh fertile egg in half lengthwise so the contents would not ooze out all over the table, this is how it would look. The yolk is the large structure in the center. As you can see, it made up of rings of yolk material which are laid down one each day. There are about 10 to 12 ring in each egg which corresponds to the number of days it takes for the yolk to develop. (Experiments have been done in which chickens were fed different colored dyes over several days. The eggs produced after the dye were colored like a rainbow.) Notice that directly on top of the yolk is the blastoderm. This is the area where the embryo will begin to form. The rest of the yolk material is food for the developing chick.
Notice the rope like structures which come out from the sides of the yolk. These structures are part of the thick albumen (egg white) and are called chalaza (sha-lay'-zuh). They serve to hold the yolk in the center of the egg instead of floating to the top. If the yolk was to float high in the albumen, the developing embryo which usually on the top of the yolk, could become stuck to the shell membrane. The presence of chalaza are indicative of fresh eggs.
Also in this picture you can see the shell, membranes and the air cell. The air cell is formed between the two membranes and is the result of moisture loss through pores in the shell.
This is a drawing of a chick embryo before it has been placed in the incubator. During the time the egg has been in the oviduct it has been developing. In fact, there may be as many as 20,000 to 60,000 cells in the embryo when the egg is laid. Notice that the embryo is a distinct round shape, and it can easily be seen with the naked eye.
This is a actual photograph of a fresh fertile egg. You can see that it has a distinct round shape. The the egg was not fertile, the round disk would simply be a small white shapeless mass. After laying, the egg can be cooled down and development will virtually cease. The embryo can remain in this state for several days until incubation begins.
Development resumes when the embryo is placed in a warm, humid environment. This could be when the hen sets on the egg or when it is placed in a incubator. An incubator is a machine which keeps eggs at a constant temperature (about 99.5o F), high relatively humidity, and gives the eggs a constant supply of fresh air (it takes the place of the hen. After 1 day at these conditions the embryo has grown tremendously. This is a photograph of an embryo late during its first day in the incubator. The embryo is at center of the of the white tissue which is the growth area of the egg. Most of the material seen here is extra embryonic membranes, tissues that will furnish nutrients, protection, and gas exchange for the developing embryo.
After about two days in the incubator blood begins to form. The blood starts some distance from the embryo in the extra embryonic tissue, as small areas of blood cells called blood islets. The heart, begins to beat after about 18 hours of incubation. Other vessels form which allow the first beats of the developing heart to draw the blood from the islets into the body. Why do you think the blood forms so early? It is so the embryo can receive enough nutrition from the yolk. As the embryo grows it requires more and more food. Since the embryo can't "eat" as it can after it hatches, the blood picks up nutrients from the yolk and brings it to the embryo. You will notice that the blood vessels will continue to enlarge as time progresses.
This is a photo of a 3 day embryo. As you can see, the blood vessels have grown to the point that it looks like a spider. At the farthest distance from the embryo the blood vessels end in a circle. This circle will continue to expand until the circulation completely surrounds the yolk, which then becomes the yolk sac.
If you look closely, you will notice that the embryo is laying on its left side. When development begins the embryo lays on its "stomach", not really but that is how it appears. As development proceeds, the embryo will turn to lay on its left side. If it turns to its right is almost never hatches. Also, the embryo appears to curl up, looking like a backwards question mark. This is normal and it will remain in this position during much of the remainder of its development.
This is a picture of a 4 day quail embryo. It is on the yolk with the some of the egg shell removed. Notice the large vessels which are required to provide the nutrients necessary for the rapid development if the embryo. The heart and eye are evident by somewhat obscured by the presence of a new membrane structure, the allantois. The allantois grows from the umbilicus (belly button) and has two primary functions. First it is a waste storage area for the embryo and it will be the gas exchange organ while the embryo is confined in the egg. After hatching, the chick will leave the allantois in the shell. The heart is the red structure in the middle of the embryo and the eye is visible as a dark area in the head.
This is a 5 day embryo which has been removed from the yolk. The embryo is inside a fluid filled sac called the amnion. The sac provides protection for the embryo. Notice the wing is beginning to form, while the legs are only very small buds. The eye is very prominent. The "bubble" on top of the head is part of the brain. At this point, all of the internal organs of the chick are present, however they are not yet functional. The chick will now begin changing shape and growing into the more familiar form of a chick.
This is a close-up picture of a 7 day embryo. It is finally beginning to look like a bird. It has a very large head with a well developed brain, large eyes, a long neck, a well formed body, partially developed wings and legs as well as a tail. On the end of the beak (white dot) the very noticeable eggtooth is present. The eggtooth has but one function, that is to help the chick to break the shell during hatching. The eggtooth will fall off a couple of days after hatching.
This 10 day embryo hasn't changed a great deal but its feathers have begun to grow. Also, the chick now has eyelids and they are nearly closed. At this point, it is about half the size it will be when it hatches.
This is a 14 day old embryo. Its growth is nearly complete. Notice how much it has changed since the last picture. Over the next couple of days the embryo will change its position in the shell. To be able to hatch, it must be in the correct position in the shell. Its head must be toward the top of the shell (blunt end). It must have its head under the right wing with its beak and eggtooth, pointing toward the air cell. Remember how small the air cell was when the egg was laid. During incubation the egg has lost quite a bit of water (about 11-12% of its pre-incubation weight) which has made the air cell much bigger. When the time is right, the chick will break the membrane of the air cell and begin to breath air for the first time. After a short time of rest, the chick will break the shell;
... and begin to breath fresh air for the first time. Finally, after several hours of hard work the chick breaks through the shell and into the world.
After just a few hours, the chick will be completely dry and look something like this photograph. Quail and chicken chicks will be up and walking, eating and chirping in just a few hours after hatching. While other birds like sparrows and finches hatch chicks which are helpless, naked, and must be fed by their parents. Each type of chick has a special name; the quail are called precocial and the sparrows are called altricial.
After about 5 to 6 weeks Japanese quail are adults and will be laying eggs of their own. This is an example of an adult male Japanese quail.
The development of the Japanese quail chick is a process which takes about 17 days to complete. Other birds require different periods of time: chickens 21 days; pheasants, partridges, and most quail, 24 days; turkeys and most waterfowl 28 days; ostriches, 42 days; and emu 53 days. The process is much the same in all avian species.