Avian Embryo
The avian embryo is amazing and exciting. In only three weeks, a small clump of cells with no characteristic features of any single animal species changes into an active, newly hatched chick. A study of this transformation is educational and interesting, and gives us insight into how humans are formed.
This publication will help you study the formation of the egg and the avian embryo. It includes plans for two small incubators so you can build one. You can buy small commercially-built incubators at stores selling farm and educational supplies.
Incubation procedures show you the effects of heat, moisture, and ventilation upon the development of the chick embryo. You also learn to hatch other fowl such as turkeys, ducks, quail, and pheasants. The publication describes how to observe and exhibit an avian embryo while it is alive and still functioning, or as a preserved specimen.
- Sections of this publication include:
- Formation and Parts of the Egg
- Stages of Embryonic Development
- Incubating and Hatching Chicks
- Constructing an Egg Incubator
- Embryology Projects
Formation and Parts of the Egg
The avian egg, in all its complexity, is still a mystery. A highly complex reproductive cell, it is essentially a tiny center of life. Initial development of the embryo takes place in the blastoderm. The albumen surrounds the yolk and protects this potential life. It is an elastic, shock-absorbing semi-solid with a high water content. Together, the yolk and albumen are prepared to sustain life - the life of a growing embryo - for three weeks, in the case of the chicken. This entire mass is surrounded by two membranes and an external covering called the shell. The shell provides for an exchange of gases and a mechanical means of conserving the food and water supply within.
A hen can produce an egg without mating. Such an egg, while edible, is not fertile and will not hatch. If a rooster mates with and fertilizes the hen, the male reproductive cell (sperm) unites with the female reproductive cell (ovum) to form a single cell that can develop into an embryo. This egg is fertile and can hatch. When an egg is opened and placed in a dish, you can see a light round spot on top of the yolk. This is the germinal disc, true ova, or female egg. At the time of lay, it is hard to tell whether or not it is fertile.
The egg is formed in the mature hen by a reproductive system composed of an ovary and oviduct. Most females have two functional ovaries, but chickens and most other birds have only one ovary and one oviduct. In early stages of embryonic development, each female chick has two ovaries; only the left one develops into a functional organ. In some birds, such as hawks, the right ovary and oviduct usually develop. A mature ovary looks like a cluster of grapes. It may contain up to 4,000 small ova which can develop into yolks. Each yolk is attached to the ovary by a thin membrane sac or follicle having a fine network of blood vessels.
The oviduct is a large, coiled tube located in the left side of the abdominal cavity. In this oviduct, all parts of the egg, except the yolk, are formed. It is divided into five distinct regions: (1) infundibulum or funnel, (2) magnum, (3) isthmus, (4) uterus or shell gland, and (5) vagina. Each male chicken has two reproductive organs called testes, located within the body about midway of the back. The testes produce sperm cells which are complementary to the egg cells of the hen. Each sperm cell has a long whip-like tail which propels it forward. The sperm are conveyed to the cloaca through the vas deferens, a tube between the testes and cloaca. After mating, the sperm travel through the hen's oviduct and concentrate in storage sites of the infundibulum.
The yolk is formed in the follicular sac by the deposition of continuous layers of yolk material. Ninety-nine percent of the yolk material is formed within the 7-9 days before the laying of the egg. The germinal disc of a developing yolk contains the single ovum cell which, after fertilization, develops into the chick. The germinal disc remains on the surface of the yolk throughout yolk formation.
When the yolk matures, the follicular sac ruptures or splits along a line with few, of any, blood vessels. This line is called "stigma." If any blood vessels cross the stigma, a small drop of blood may be deposited on the yolk as it is released from the follicle. This causes most blood spots in eggs. After the yolk is released from the follicle, it is kept intact by the vitelline membrane surrounding it. The release of the yolk from the ovary is called "ovulation."
After its release from the follicle, the yolk falls into the hen's abdominal cavity. The infundibulum of the oviduct quickly engulfs the yolk with its thin, funnel-like lips. If, for some reason, the infundibulum is unable to pick up the yolk from the body cavity, the body will reabsorb the yolk. A hen that consistently fails to pick up the yolks from the body cavity is called an internal layer.
After the yolk is engulfed by the infundibulum, fertilization of the ovum follows almost immediately. Sperm cells from the male are stored in glands or nests located in the infundibulum, and are released when the yolk passes by. A sperm cell must penetrate the thin vitelline membrane and reach the female cell to complete fertilization. The vitelline membrane thickens as the rest of the egg is formed.
The yolk quickly enters the magnum section of the oviduct where the dense portion of the albumen is added. The albumen serves as a shock-absorbing substance and feeds the developing embryo. The shape of the egg is largely determined in this section.
The magnum is divided from the isthmus by a narrow, translucent ring without glands. The isthmus is smaller in diameter than the magnum. It is here the two shell membranes form. The shell membranes loosely contain the yolk and dense white until the rest of the albumen is added in the uterus.
The shell is added in the uterus or shell gland portion of the oviduct. The shell is composed mainly of calcium carbonate. It takes about 20 hours for the egg shell to form. If the hen lays brown eggs, the brown pigments are added to the shell in the last hours of shell formation.
The chalazae, two cord-like structures which keep the yolk centered in the egg, first appear in the uterus. The chalazae also function as an axis around which the yolk can rotate and keep the germinal disc uppermost at all times.
In the last portion of the oviduct, the vagina, a thin coating called "bloom" is applied to the shell to keep harmful bacteria or dust from entering the egg shell pores. The egg passes through the oviduct small end first, but is laid large end first. In the vagina, the egg is turned horizontally just before laying. If the hen is disturbed on the nest, the egg may be prematurely layed small end first. Oviposition is the act of pushing the egg from the oviduct.
When an egg is laid, it fills the shell. As it cools, the inner portion of the egg contracts and forms an air cell between the two shell membranes. A high quality egg has a tiny air cell, indicating the egg was collected soon after being layed and was stored properly. The air cell is usually located in the large end of the egg where the shell is most porous and air can enter easily. The chick punctures and breathes through his air cell just before hatching.
Life in Twenty-one Days
One of the greatest miracles of nature is the transformation of the egg into the chick. A chick emerges after a brief three weeks of incubation. The complexity of the development cannot be understood without training in embryology.
Cell division begins soon after fertilization, even while the rest of the egg is being formed. Cell division will continue if the egg is kept warmer than 67oF. The first cell division is completed about the time the egg enters the isthmus. Additional cell divisions take place about every 20 minutes; so, by the time of lay, several thousand cells form two layers of cells called a "gastrula."
At this time the egg is laid, it cools, and embryonic development usually stops until proper environmental conditions are established for incubation. After incubation begins, the cellular growth resumes. At first, all the cells are alike, but as the embryo develops, cell differences are observed. Some cells may become vital organs; others become a wing or leg.
Soon after incubation is begun, a pointed thickened layer of cells becomes visible in the caudal or tail end of the embryo. This pointed area is the primitive streak, and is the longitudinal axis of the embryo. Before the first day of incubation is through, many new organs are forming. The head of the embryo becomes distinguishable; a precursor of the digestive tract, the foregut, is formed; blood islands appear and will develop later into the vascular or blood system; the neural fold forms and will develop into the neural groove; and the eye begins.
On the second day of incubation, the blood islands begin linking and form a vascular system, while the heart is being formed elsewhere. By the 44th hour of incubation, the heart and vascular systems join, and the heart begins beating. Two distinct circulatory systems are established, an embryonic system for the embryo and a vitelline system extending into the egg.
In later stages of embryonic development, there are two distinct extra-embryonic blood systems. One system, the vitelline system, transports nutrients from the yolk to the growing embryo. Before the fourth day, it oxygenates blood. The other blood system, made of allantoic vessels, is concerned with respiration and the storage of waste products in the allantois. When the chick hatches, both circulatory systems cease to function.
On the second day, the neural groove forms and the head portion develops into the parts of the brain. The embryo is developed enough that flexion and arching of the embryo begins, the ears begin development, and the lens in the eyes are forming.
At the end of the third day of incubation, the beak begins developing and limb buds for the wings and legs are seen. Three visceral clefts (gills) have formed on each side of the head and neck. These formations are important in the development of the arterial system, eustachian tube (in the ear), face, jaw, and some ductless glands. The fluid-filled amnion has surrounded the embryo to protect it: it helps maintain proper embryonic development. The tail appears, and the allantois is seen. The allantoic vesicle is a respiratory and excretory organ. Nourishment from the albumen and calcium from the shell are transported to the embryo through the allantois.
Torsion and flexion continue through the fourth day. The chick's entire body turns 90o and lies down with its left side on the yolk. The head and tail come close together so the embryo forms a "C" shape. The mouth, tongue, and nasal pits develop as parts of the digestive and respiratory systems. The heart continues to enlarge even though it has not been enclosed within the body. It is seen beating if the egg is opened carefully. The other internal organs continue to develop. By the end of the fourth day of incubation, the embryo has all organs needed to sustain life after hatching, and most of the embryo's parts can be identified. The chick embryo cannot, however, be distinguished from that of mammals.
Many complex physiological processes take place during transformation from the egg to the chick. They include: the use of highly nutritious food materials in the egg; the respiration of gases, or the taking in of oxygen and the removal of carbon dioxide; and the building of living energy within the chick.
The embryo grows and develops rapidly. By the seventh day, digits appear on the wings and feet, the heart is completely enclosed in the thoracic cavity, and the embryo looks more like a bird. After the tenth day of incubation, feathers and feather tracts are visible, and the beak hardens. On the fourteenth day, the claws are forming and the embryo is moving into position for hatching. The supply of albumen is exhausted by the sixteenth day, so the yolk is the sole source of nutrients. After twenty days, the chick is in the hatching position, the beak has pierced the air cell, and pulmonary respiration has begun. The yolk sac is contained completely within the body cavity in preparation for hatching.
The normal position of the chick for hatching is with the head in the large end of the egg, under the right wing, with the legs drawn up toward the head. If the head is positioned in the small end of the egg, the chick's chances of survival are reduced by at least one-half. This is a serious malposition, or wrong position, for hatching. Just as a wrong position makes birth more difficult in mammals, a wrong position of the chick makes hatching more difficult, or impossible.
After 21 days of incubation, the chick finally begins its escape from the shell. The chick begins by pushing its beak through the air cell. The allantois, which has served as its lungs, begins to dry up as the chick uses its own lungs. The chick continues to push its head outward. The sharp horny structure on the upper beak (egg tooth) and the muscle on the back of the neck help cut the shell. The chick rests, changes position, and keeps cutting until its head falls free of the opened shell. It then kicks free of the bottom portion of the shell. The chick is exhausted and rests while the navel openings heal and its down dries. Gradually, it regains strength and walks. The incubation and hatching is complete. The horny cap will fall off the beak within days after the chick hatches.
Newly-hatched chicks can be shipped long distances (up to 72 hours travel time) without food. Provide chicks with feed and water on the first day of life so they can learn to eat and drink immediately. The yolk is largely unused by the embryo and is deposited within the chick's body on the 19th day, just before it hatches. The yolk is highly nourishing and provides proteins, fats, vitamins, minerals, and water for several hours after hatching. The yolk is consumed gradually during the first ten days of the chick's life.
EVENTS IN EMBRYONIC DEVELOPMENT
- Before Egg Laying:
- Fertilization
- Division and growth of living cells
- Segregation of cells into groups of special function (tissues)
- Between Laying and Incubation
- No growth; stage of inactive embryonic life
- During Incubation:
- First day
- 16 hours - first sign of resemblance to a chick embryo
- 18 hours - appearance of alimentary tract
- 20 hours - appearance of vertebral column
- 21 hours - beginning of nervous system
- 22 hours - beginning of head
- 24 hours - beginning of eye
- Second day
- 25 hours - beginning of heart
- 35 hours - beginning of ear
- 42 hours - heart beats
- Third day
- 60 hours - beginning of nose
- 62 hours - beginning of legs
- 64 hours - beginning of wings
- Fourth day - beginning of tongue
- Fifth day - formation of reproductive organs and differentiation of sex
- Sixth day - beginning of beak
- Eighth day - beginning of feathers
- Tenth day - beginning of hardening of beak
- Thirteenth day - appearance of scales and claws
- Fourteenth day - embryo gets into position suitable for breaking shell
- Sixteenth day - scales, claws and beak becoming firm and horny
- Seventeenth day - beak turns toward air cell
- Nineteenth day - yolk sac begins to enter body cavity
- Twentieth day - yolk sac completely drawn into body cavity; embryo occupies practically all the space within the egg except the air cell
- Twenty-first day - hatching of chick
- Fifth day - formation of reproductive organs and differentiation of sex
From A.L. Romanoff, Cornell University Extension Bulletin 205
Incubating and Hatching Chicks
Getting and Caring for Hatching Eggs
In urban areas, getting hatching eggs may be a problem. Remember: eggs purchased from your local grocery store are not fertile and will not hatch. Egg producers supplying the stores with market eggs do not keep roosters with hens. Hatching eggs can be purchased from most poultry breeding farms. For a list of hatching egg sources, contact your county agent. If possible, go to the farm and bring the eggs home yourself rather than having them shipped or mailed. It is difficult for the post office or transport companies to provide proper shipping conditions for small orders of hatching eggs.
Often careful attention is given to incubating and rearing chicks, but none given to the care of the eggs before incubation. As we learned earlier, embryo development occurs even before the egg is layed. The best hatching eggs will suffer with reduced hatchability unless provided with proper care between oviposition and incubation.
It may not be practical for you to place the eggs in an incubator as soon as you get them. If not, keep them in a cool, humid room. The best storage conditions are near 55oF. with 75 percent humidity. The vegetable section of your refrigerator is a suitable area. The temperature should not drop below 40oF. or hatchability will be reduced. The cool temperature will delay embryonic growth until incubation begins, and the high humidity will keep the eggs from drying out.
Incubate the eggs as soon as possible to prevent reduction in hatchability. The hatchability of eggs older than seven to ten days decreases rapidly; at three weeks, it reaches zero percent. If the eggs are not incubated within three to four days, turn them daily. Turning the eggs prevents the yolks from touching the shell and injuring the embryo. Plan ahead to avoid storage problems and reduced hatches.
Don't save excessively dirty eggs for hatching. These eggs can contaminate other eggs or chicks. Clean slightly soiled eggs by sanding them lightly with fine sandpaper. Don't sand them hard enough to make the shell thin or weak. Never wash hatching eggs because this forces bacteria through the shell and into the eggs.
The eggs should warm to room temperature before being placed in the incubator. The shock of warming the eggs too rapidly will cause moisture to condense on the shell; this may lead to disease or a reduced hatch.
Incubation Procedures
Because the incubator is not well insulated and will be opened frequently when the eggs are turned, keep the machine in a room where the temperature is between 70o and 75oF. (Normal room temperatures are satisfactory.) Do not place the incubator near windows where it may be exposed to the direct rays of the sun or near cold walls.
There are two basic types of incubators available, forced-air and still-air incubators. In forced-air incubators, fans provide internal circulation. The capacity of these units may be large. The still-air incubators are usually small and have no fans for air circulation. Air exchange is made by escaping warm, stale air at the top and entering cooler, fresh air at the bottom. Recommended temperatures will vary between the two incubators, so follow the manufacturer's recommendations. All references to incubators are directed to the still-air incubators except where noted.
Clean and disinfect the incubator before each use. Wash the unit with a warm detergent solution and rinse with a disinfectant solution. This reduces the chances of carrying disease-causing organisms from one batch of eggs to another.
Start the incubator a day or two before setting the eggs. Turn on the heat and place water in the tray so proper incubation conditions can be obtained. Place a thermometer in the incubator so the bulb is one inch above the screen floor, close the incubator, and adjust the thermostat until the temperature stays between 101o and 102oF. Be careful that the bulb of the thermometer does not touch the eggs or side of the incubator. The sides and top of the incubator should fit together securely to prevent heat loss.
To get the best possible hatch, keep the temperature as close to 102oF. as possible for the complete incubation period. There will be minor fluctuations of 1oF. above and below the desired temperature, but there should not be prolonged periods of high or low temperatures. Hatching eggs can take an amazing amount of abuse because they are well protected and insulated, but they are sensitive to extreme heat. Operating the incubator at 105oF. for 30 minutes will harm many embryos, but operating at 90oF. for three to four hours will merely slow the rate of growth. Maintain a forced-air incubator at 100oF. for best results.
Check the thermometer! Is it accurate? An error of one degree for 21 days can seriously interfere with an embryo's growth. To check the incubator thermometer, place the bulb next to the bulb of a clinical (oral kind used to check body temperature) or a laboratory thermometer. Hold them under lukewarm water and compare the readings. Both should read the same temperature, so make adjustments for any error in the incubator thermometer. A thermometer in which the mercury column is separated will not give an accurate reading. Discard it.
Humidity must be carefully controlled to prevent unnecessary moisture loss from the eggs. A device often used to measure humidity inside an incubator is the hygrometer. Readings from a hygrometer are measured in "degrees, wet bulb." Use the table to convert hygrometer readings to relative humidity. The relative humidity in the incubator for the first 18 days should remain at 58-60 percent or 87o-89oF., wet bulb. Increase the humidity during the last three days of incubation to at least 65 percent relative humidity or 90o-94oF., wet bulb.
Relative |
Wet Bulb Readings |
|||
99o |
100o |
101o |
102o |
|
45% |
80.5 |
81.3 |
82.2 |
83.0 |
Rarely is the humidity too high in a still-air incubator. The water pan should cover at least one-half of the surface area of a still-air incubator. At hatching time, place another pan of water or a wet sponge in the incubator to increase the humidity by increasing the exposed water surface area. Chicks need to be saturated before they can hatch properly, but do not drown them. High humidity will produce a late hatch; low humidity will produce an early hatch. Low humidity will also cause the chick to stick in the shell and die at hatching time.
Proper ventilation is vital. During embryonic development, oxygen enters the egg through pores in the shell and carbon dioxide escapes in the same manner. As the chicks begin to hatch, they must receive an increasing supply of fresh air. As the embryos grow, gradually open the air openings of the incubator to increase the air flow. Be sure to avoid reducing the humidity during the hatching period. Provide ventilation openings both above and below the eggs for proper air exchange. Never place more than on layer of eggs in a still-air incubator.
If the electric power fails, the eggs will fare best if left alone to conserve the heat and humidity within the incubator. If the incubator is the forced-air type, open the incubator immediately and let fresh air enter. Maintain the room temperature at 75oF. or more.
Turn the eggs at least two or three times daily during the first 18 days of incubation. Turning keeps the embryo from sticking to the shell membranes when left in one position too long. DO NOT turn eggs during the last three days before hatching. The embryos are moving into hatching position and do not need to be turned.
An excellent method to tell of all eggs have been turned is to mark an "X" on one side of the shell and an "O" on the opposite side. You can always tell if the eggs have been turned by noting which side is up. Write the marks with a pencil so harmful chemicals do not enter the eggs. When turning, be sure your hands are clean and free of greasy or dusty substances. During the first week of incubation, turn eggs carefully because the developing embryos have delicate blood vessels that may be ruptured if jarred or shaken.
Mark eggs incubated on different days with the date you placed them in the incubator. This prevents eggs from being overlooked and left in the incubator after they should have hatched. The eggs should be set and maintained vertically with the large end up, or horizontally with the large end slightly elevated. This will let the embryo stay in the proper position for hatching.
Chicken eggs require 21 days to hatch, but the incubation periods for the eggs of other species of poultry vary. The approximate periods of incubation required for various species of poultry and game birds are:
Chicken |
21 days |
When the hatch is completed, disconnect the incubator and remove all chicks, shells, and unhatched eggs. Wash the interior of the incubator with a warm detergent solution. If the incubator is to be used immediately, rinse it with a disinfectant solution. After the incubator has dried thoroughly, store it for later use.
Constructing an Egg Incubator
Small incubators, suitable for use in the home, can be purchased from stores that sell farm equipment. An egg incubator can be built at home with a little work and expense. This publication contains plans for two still-air incubators.
The first incubator is constructed from a styrofoam ice chest. It is inexpensive, and because it is insulated, is inexpensive to operate. It can be damaged easily. The eggs and chicks can be observed through a window in the lid. This incubator will hold about 40-45 eggs.
The second incubator is more expensive, but is more permanent. It is constructed of plywood and glass, and will accommodate up to 100 large eggs. Both incubators are heated by a commercially available heating cable. The heating cable can be replaced with two or three ordinary light bulbs. Get a list of organizations that sell incubator supplies and equipment from your county agent or state poultryman.
Styrofoam Incubator
You'll need the following equipment and supplies to construct this incubator.
- Styrofoam ice chest (12-16" x 20-24" x 12"-15")
- Heating cable
- Micro-switch assembly (thermostat)
- Glass (approx. 10"x14")
- ¼" welded wire - hardware cloth (24"x36")
- Cake tin (9"x14"x1½")
- Thermometer
- Masking tape
Plywood Display Incubator
This incubator is more expensive and will take longer to construct than the styrofoam incubator, but it is more durable. It is built of ½-inch exterior or marine grade plywood and glass, and will accommodate up to 100 large chicken eggs. Building plans for this incubator are shown by clicking on the illustration.
1 pc |
1/2"x4'x6' A-C Exterior Plywood |
*electrification kit composed of wafer thermostat with duplex outlet, pilot light, service cord, and 160-watt flexible glass-covered heating element.
Both incubators are heated by a commercially available glass-covered heating element. For the plywood incubator, it should provide 160 watts of heat. Slightly less heat is required in the styrofoam incubator.
Hatching Failures
Eggs do not hatch for reasons which may or may not be the fault of the person caring for the eggs. Below are a few common reasons for incubation failures.
- Infertile eggs. Buy fertile hatching eggs from farms having at least one rooster with every ten hens. Avoid seasonal temperature problems by getting hatching eggs in the spring.
- Parent stock are weak, unhealthy, or fed a nutritionally deficient diet. Buy eggs from farms that care for the breeder flock by following sound poultry management practices.
- Eggs are too old or improperly cared for before incubation. Care for the eggs as described. Do not store eggs for longer than 7-10 days before incubating.
- Shell contamination. Incubate only clean or slightly dirty eggs cleaned with sandpaper. Do not wash dirty hatching eggs or allow eggs to sweat before placing them in the incubator.
- Temperatures too high, too low, or too variable. Check incubator temperatures with an accurate thermometer, and adjust the thermostat accordingly.
- Too little or too much humidity in the incubator. Obtain a hygrometer and measure the humidity before making further adjustments.
- Eggs not turned often enough. Turn eggs at least two or three times daily. Commercial hatcheries turn eggs every two hours.
- Improper ventilation resulting in oxygen starvation. Be sure all ventilation holes are open in still-air incubators. Forced-air incubators should start with vent openings half-opened. Increase ventilation after ten days until openings are fully opened at hatching time.
- Rough handling of eggs. Ordinary handling does not harm the embryo because of the protection provided by the egg and amniotic fluid. Excessive handling and jarring of eggs while turning, especially during the first week, may be harmful.
Embryology Projects
Coloring Chick Embryos
The main purposes in coloring embryos are to provide a practical method of identifying chicks from different groups of eggs and so you can watch their movements after they leave the nest. In wildlife management studies, where identification and observation of ducks is difficult, identification and observation are made easy by coloring the embryos with bright dyes.
The coloring of chick embryos provides the practice necessary to become skilled in the coloring technique while acquainting you with the tools and supplies used by students, researchers, and professional people.
Equipment and Supplies
1 large beaker (1000 ml) or pan |
Procedure
Put water in the large beaker or pan and place it over heat. Loosen tops of bottles containing dye and place them upright in the small beaker or glass. The tops are loosened so the bottles of dye will not explode when heated. Put syringe, needles and drill in same container with the bottles of dye. Add about 1½-inch distilled water to the small container and place in the larger container until the water in the larger container has boiled for 20 minutes. Remove from the heat, pour the water out of the small container, and allow the contents to air dry as they cool.
At a spot about ½-inch from the small end of the egg, daub an area about one-inch in diameter with merthiolate. Dip the tip of the dental drill in merthiolate. Rotate the drill between the fingers while gently pressing the tip against the shell in the center of the daubed area. Rotate until a hole is made through the shell.
Assemble the syringe and needle. Be sure they do not become contaminated by contact with foreign objects. Dip the needle in the merthiolate, and withdraw ½ cc. (cubic centimeter) or .5 ml. (milliliter) of dye. Insert only the tip of the needle in the hole and through the shell membranes. To prevent overflow, gently and slowly inject the dye. Remove the needle, seal the hole with paraffin, and return the egg to the incubator. Clean the syringe and needle by flushing them with distilled water each time a different color dye is used.
Dyes can be mixed to produce colors other than those available at local stores. They can be injected into chicken, duck, goose and other species of eggs.
Hatching Chick Exhibit
About three to four dozen fertile eggs should be set 20 days before each date on which the hatching chicks are to be displayed. To assure chicks hatching at all hours on the day of the exhibit, set one-third of the day's hatch eight hours earlier and another one-third eight hours later than the normal setting time. A reasonable sequence of chicks should emerge from the eggs during the exhibit hours if there is reasonable good fertility and hatchability.
Chick Embryo Exhibit
The chick embryo exhibit need display only the 1, 2, 3, 4, 5, day embryos, any one embryo from 6 to 10 days, any one embryo from 11 to 18 days, and any one embryo from 19 to 21 days. The abbreviated exhibit is preferred to the full 21 day exhibit because it requires fewer eggs, uses a smaller incubator, and shows the development of the chick embryo just a well as the 21-day exhibit.
For a one- to six-day exhibit of the embryonic development of living embryos, the incubation schedule should be:
Length of the Show (days) |
||||||
One |
Two |
Three |
Four |
Five |
Six |
|
Days before show * |
Eggs to Set |
|||||
18 |
5 |
8 |
8 |
8 |
8 |
8 |
* This schedule is based on 80% fertility and 80% hatchability of fertile eggs. |
Displaying Living Chicken Embryos
Learn to open incubated chicken eggs so you can see the day-by-day growth of the living embryo as it develops within the egg. This is an interesting and exciting activity in which you can observe the fascinating growth and development of a chick embryo. After you learn to open incubated eggs, you can show someone else how to observe the developing embryo.
While preparing the embryos, you will use tools similar to those doctors use when they perform delicate operations, and you will learn the scientific names of parts of the embryo common to unborn babies, even human babies. You will use your fingers and your eyes to do a delicate task that would require great care of the most experienced doctors, laboratory technicians and research people. With practice, you will soon open the eggs with ease.
Equipment and Supplies
Incubator |
How to Open the Incubated Egg
Refer to the illustrations of the fresh egg and embryonic membranes. Locate the parts of the egg described in the following paragraphs by referring to the material in "Formation and Parts of the Egg."
Incubate four fertile eggs for 48 hours. Crack the shell at the large (air cell) end by tapping gently with the heavy end of the forceps. Remove a few flakes of shell with the forceps and then, using the manicure scissors, with a circular motion cut away the shell extending above the contents of the egg. As the shell is cut away, the outer shell membrane is removed with it. The inner shell membrane is the opaque (white) membrane lying across the fluid portion of the egg. This must be removed so that the embryo may be seen clearly.
Place a drop of water on the inner shell membrane. Now gently pick at the moistened portion until it is grasped by the forceps. Caution: Do not rupture the blood vessels or the thin membrane of the allantoic sac.
Use a circular motion while removing the membrane. If the membrane is uncovered successfully, the contents of the egg are exposed. The yolk is covered with a mass of blood vessels, the vitelline circulation, and the tiny heart lies pulsating with life.
After the inner shell membrane has been removed, place the egg on a pedestal in the incubator. The eggs must be kept in the incubator except when they are being prepared for display or are being observed. After being placed on the pedestal, the embryo will soon come into position so it can be seen easily through the window made by removing the shell. Use the magnifying glass to look closely at the heart and the first faint traces of the eye developing in the three day embryo.
By breaking a fresh egg and an egg incubated for one day into dishes and then making windows in eggs incubated for 2, 3, 4, 5 and more days, the sequence of growth and development of the chick embryo can be followed easily.
Preservation of the Avian Embryo
A series of stages of avian embryo development can be prepared easily. Such a series of embryos can provide a ready reference set for student use. Use specimens from two days to hatching for this purpose.
Equipment and Supplies
Alcohol (ethanol or isopropanol) |
Crack the shell of the egg at the broad end with a sharp knife or scalpel, and pick away the pieces until an opening about one-inch in diameter is made. Remove the outer and inner shell membranes. The embryo in the blastoderm will be uppermost. Using fine-pointed scissors, cut out a circle of blastoderm about the size of a quarter, leaving the embryo at the center. With blunt forceps, pull the embryo and adherent extra-embryonic membranes away from the yolk and albumen. Remove all membranes and sever the umbilical stalk near the body wall. Rinse well under tap water. After washing clean, place the embryo into a bottle containing 10% formalin. The formalin solution is made of one part of the 37% formaldehyde solution and nine parts of water. This solution will preserve the specimen. After a week, pour off the formalin solution, rinse the specimen in tap water, drop 3 to 4 drops of glycerin onto it and place it into 70% alcohol as a final preservation agent. The glycerin keeps the specimen softer and the skin translucent.
Dip the top of the container into melted wax to seal against evaporation of the alcohol. Label the containers with detailed information -- date, variety of embryo, name of preparer, preservative. Note: When dealing with embryos under five days of incubation, the following technique is helpful in harvesting the embryo. After the embryo is exposed from under the shell membranes, place about four drops of the formalin solution on the embryo. The solution coagulates the protein and makes it easier to harvest the embryo.
A Glossary of Terms and References used in this publication is available.
By Dr. Tom W. Smith, Emeritus Professor of Poultry Science, Mississippi State University
Mississippi State University does not discriminate on the basis of race, color, religion, national origin, sex, age disability, or veteran status.
Publication 1150
Extension Service of Mississippi State University, cooperating with U.S. Department of Agriculture.
Published in furtherance of Acts of Congress, May 8 and June 30, 1914. RONALD A. BROWN, Director.
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