} Bulletin 633 (4-R ICSJ

THE AVIAN EMBRYO A MANUAL OF EMBRYOLOGY AND INCUBATION

COOPERATIVE EXTENSION SERVICE The Ohio State University

Assistant State Lead.Pl', and Professor of Poultry Science,

matPrials used Emil l\1alinovsky, former Extension Poultry SpPclalist at The Ohiu Stdte University, and from material from the Northeast Cooperative Publication-From Egg to Chick

Purpose Most young people are fascinated by the of

life. This publication is designed to help them under­stand some of the theory and prmciples of reproduction. Specifically, the experiences included in the text will provide an opportunity for them to:

- Learn about the avian egg. - Study the reproductive system and fertilization. - Understand embryo development. - Comprehend the incubation process. - Make and use an incubator. - Incubate and hatch eggs. - Observe live chicks.

Trade names are used in this manual solely for the purpose of providing specific mformation Mention of a trade name dues not constitute a guarantee or warranty of the product named, nor does 1t signify approval of the product to the exclus10n of other comparable products

All educational programs and activities conducted by the Oh10 Cooperative Extension Service are available to all potential chentele on a nond1scrimmatly basis without regard to race, color. or national origin

101\11

The Egg The avian egg is a marvel of nature's architecture. A

highly complex reproductive cell, it is essentially a very small center of life, a world of its mNn.

ScienUfically an egg (ovum) is the repro-ductive cell by the female. It remams a cell when fertilized by the single cell of the male sperm. then has a full ""''"'"'""'"'~ sames and genes.

The compleled single cell (zygote) then rapidly di­vides into 2 cells. 4, 8, 16, 32, 64, and so on, until the faint outhne of a developmg embryo and a network of blood vessels surrounding the yolk can be seen.

is normally called 'an egg' [the chicken egg, for example) is a much more complex structure designed to nourish and protect the embryo growing from the zy­gote. The chicken egg differs from the mammalian egg because it contains its own built in food . A vig­orous, healthy chick can be hatched from a fertile egg. The egg needs only a warm, humid environment while the embryo in maturing.

Although human nutritional requirements are not the same as those of the chick, they are similar in so many respects that the egg has become a convenient, econom­ical source of many of the essential proteins, minerals, and vitamins necessary to our good health. As we know it, 'the egg' ls the single most complete food known to man. Versatile and nutritious, it is used every day in the preparation of the most common or the most fanciful meals.

The Parts of the Egg

Looking at the egg from the outside we see the shell, which is a hard, protective covering composed primar­ily of calcium carbonate. (See figure 1.) The shell is porous and the pores at the large end are larger and more numerous than those at the small end. (There are about 7 ,000 pores in a chicken egg shell.) This permits the transfer of gases through the shell. Carbon dioxide and moisture are given off through the pores and are re­placed by atmospheric gases, including oxygen.

Immediately beneath the shell are two membranes, the outer and inner shell membranes. These membranes protect the contents of the egg from bacterial invasion and prevent rapid evaporation of liquid from the egg.

d in furtherance of CoQperative Extension work, acts of May 8 and June 30, 1914, In cooperation with the U.S. Department of Agriculture. Roy M. W:ottman, Director of the Coopetative Extension Service, The Ohio State University.

Because the body temperature of a hen is approxi­mately 107°F., eggs are this temperature at the time they are laid. The temperature of the air is usually much lower than 107°F., and the egg cools to the temperature of its surroundings. As cooling takes place, the contents of the egg contract more than does the shell of the egg. This creates a slight vacuum and air is normally drawn through the pores in the large end of the shell with the resultant formation of an air cell between the inner and outer shell membranes.

As a result, the large end of the egg is called the air-cell end. On the 2oth day of incubation the chick pushes its beak through the shell membranes into the air cell (which by this time has greatly enlarged) and draws its first breath of air from this space.

The albumen located between the shell membrane and the yolk provides a large amount of the protein necessary for proper development.

The yolk contains large amounts of fat and protein. The egg white (albumen) is almost pure, high-quality protein. The yolk is also a reservoir of the vitamins and minerals that are essential for normal growth. These substances are used along with the oxygen taken in through the pores of the shell, and provide an abundant source of metabolic energy for the embryo. Byproducts of this process are carbon dioxide and water. Water is used by the embryo to replace moisture lost through evaporation. Carbon dioxide is transpired through the pores of the shell. Calcium absorbed from the yolk and shell is used by the embryo to make its bone structure, or skelton.

The Reproductive System and Fertilization

The Hen

The reproductive system in the female chicken is in two parts: the ovary and the oviduct. Unlike most female animals, which have two functioning ovaries, the chic­ken usually has only one. The right ovary stops develop­ing when the female chick hatches, but the left one continues to mature.

Ovary. The ovary is seen as a cluster of developing yolks, attached to the back about midway between the neck and the tail. (See figure 2.) It is fully formed when the chicken hatches and contains several thousand tiny ova, each ovum within its own follicle or sac. As the female reaches sexual maturity, these ova enlarge greatly a few at a time into yolks.

Oviduct. The oviduct is a tubelike organ lying along the backbone between the ovary and the tail. In a mature hen, it is approximately 25 to 27 inches long. The yolk is completely formed in the ovary. When a yolk is fully

3

Late bra Blastoderm (germinal disci

Albumen Yolk

Air cell

Inner and outer shell membrane Shell

Figure 1. Parts of an egg.

Figure 2. Location of the ovary and oviduct.

developed, its follicle or sac ruptures, releasing it from the ovary It then enters the infundibulum or entrance of the oviduct.

All of the other parts of the egg are added to the yolk as 1t passes through the oviduct The chalazae, albumen, shell membranes, and shell are formed around the yolk to make the complete egg, which is then laid. This com­plete cycle usually requires a little more than 24 hours. About 30 minutes after the egg is laid, another yolk is released and the process repeats itself. The function of each of the parts of the oviduct is shown in figure 3.

The Rooster

The male fowl has two testes which are situated high up in the abdominal cavity, along the back. These never descend into an external scrotum, as is the case with other farm animals.

Testis. The testis consists of a large number of very slender, much-convoluted ducts, from the linings of which the sperm are produced. These ducts appear in groups separated by delicate membranes which extend inward from a membrane surrounding the testis. They all lead eventually to the deferent duct. a tube which conducts the sperm outside the body.

Al OVARY

B/ OVIDUCT

1. lnfundlbulum 2.Magnum 3. Isthmus 4. Uterus 5. Vagina 6. Cloaca 7. Vent

Figure 3. Reproductive system of the hen.

4

Papilla. Each deferent duct opens into a small papilla, and together the papilla serve as an intromittent organ. They are located on the dorsal wall of the cloaca.

The rooster responds to light in the same manner as does the hen. Increasing day length causes release of hormones from the pituitary gland. These in turn cause enlargement of the testes, androgen secretion, semen production, and stimulate mating behavior. Males used as breeders need to be lighted properly for maximum fertility, and should not be lighted to stimulate gonad development until they will be used.

Fertilization When a rooster mates with a hen, it deposits sper­

matozoa in the cloaca of the oviduct. These sperm, con­taining male germ cells, travel the length of the oviduct and are stored in the infundibulum.

On the surface of every egg yolk there can be seen a tiny, whitish spot called the blastodisc. This contains a single female cell. When a yolk enters the infun­dibulum, a sperm penetrates the blastodisc, fertilizing it. The blastodisc becomes a blastoderm. Technically, it is the true egg. Shortly after fertilization, the blastoderm begins to divide into 2, 4, 8, and more cells. The first stages of embryonic development have begun and con­tinue until the egg is laid. Development then subsides as the egg cools until the egg is incubated.

Selection and Care of Hatching Eggs

Obtaining Hatching Eggs

Obtaining fertile eggs may present a problem, espe­cially if you live in an urban area. Most of the eggs sold in food stores are not fertile, and cannot be used for incubation. Fertile eggs can usually be obtained from hatcheries or poultry breeding farms. Some large hospi­tals may also be able to provide them. Contact your county Extension office for suggestions.

Before you begin the project, consider what will be done with the chicks that are hatched. If possible, line up someone who has experience in rearing chickens and is willing to take the chicks. Do not hatch chicks and then abandon them or give them to someone who is unable to care for them properly.

When you have located a source of fertile eggs, pick them up yourself rather than having them shipped or mailed. It is difficult for hatcheries, the postal service, or transportation companies to handle small orders of eggs properly.

Care of Eggs Before Incubation Begins

Fertile eggs should be set within 10 days after they are laid. Shells should be sound; cracked eggs do not hatch well. If it is necessary to hold the eggs before setting,

keep them at a temperature of 50° to 60°F. Refrigerator temperatures are usually too cold, and embryo de­velopment will begin ifroom temperature exceeds 75°F. It is best to have an incubator ready for the eggs when you pick them up. Plan to set the eggs so that they will begin to hatch at a time when children will be able to observe the process.

Incubating the Eggs Incubation means maintaining conditions favorable

for developing and hatching fertile eggs. Still-air in­cubators do not provide mechanical circulation of air. Circulating-air incubators are equipped with electric fans. Optimum operating temperatures differ slightly.

Four factors of major importance in incubating eggs artifically are: temperature humidity, ventilation, and turning. Of these factors, temperature is the most criti­cal. The temperature of the broody hen is slightly lower than the nonbroody hen's average 107°F.

Artificial inculbation is most easily accomplished through the use of still-air incubators. Thermostatically controlled electric units are most convenient for clas­sroom incubation.

Constructing an Egg Incubator* The small amount of work and expense involved in

the building of an egg incubator will prove to be reward­ing to those persons who wish to study embryonic de­velopment for a science project. The construction pro­ject can well be a joint project for the school classroom and for the family.

Installation of Heating Assembly

Microswitch or snap action thermostat unit is instal­led 5 inches above egg tray at one end of machine near the front. Lamp cord is passed into machine through a small hole and is fastened to one connector on the unit. Porcelain lamp bases are installed at each end of the incubator at a level that will easily clear the egg tray. On the end carrying the thermostat, the base is mounted away from the thermostat. Using plastic coated wire the lamp bases are wired in series with the thermostat unit. The remaining lamp cord wire is attached by means of a solderless connector to a short piece of plastic coated wire. Attachment of this wire to a lamp completes the circuit. Sketch 8

To hold the thermometer, fold 4 x 6 inch pieces of stiff cardboard lengthwise to form a "tent". Fasten ther­mometer horizontally to cardboard at level of the top of eggs to be hatched. For chicken eggs this is 1 % inch. Thermometer is placed in center of egg tray. Thermome­ter must not actually touch eggs during incubation period.

* Incubators can be purchased from Sears; Montgomery Ward, Brower Mfg Co., Quincy, Illinois, Lyon Electric Co , P.O. Box 81303, San Diego, California 92138.

5

Humidity

The relative humidity of the air within an incubator for the first 18 days should be about 60 percent. During the last 3 days (the hatching period) the relative humid­ity should be nearer 70 percent. Too much moisture in the incubator prevents normal evaportation and results in a decreased hatch. Too little moisture results in ex­cessive evaporation, causing chicks to stick to the shell at hatching time.

During the hatching period, the humidity in the in­cubator may be increased by using an atomizer to spray a small amount of water into the ventilating holes. (This is especially helpful when duck or goose eggs are being hatched.)

An 8-inch pie tin or cake pan containing water and placed under the tray of eggs should provide adequate moisture. The relative humidity in the incubator can also be varied by changing the size of the water pan or by putting a sponge in the pan to increase the evaporating surface. The pan should be checked regularly while the incubator is in use to be sure that there is always an adequate amount of water in it.

During the latter stages of incubation (from the 19th day on) condensation on the glass indicates the presence of sufficient moisture. The condensation is also related to the temperature of the room where the incubator is being operated, however. There will be more condensa­tion on the glass if the room is cold, so be sure the temperature in the incubator remains steady at 101°F.

Location of Incubator

Since the incubator is not too well insulated and will be opened frequently when eggs are turned, it is desira­ble that this machine be kept in a room where the temp­erature is between 70° - 75° (classroom temperatures are satisfactory). Do not place the incubator near windows where it will be exposed to the direct rays of the sun or near cold walls.

Incubator Operation

Start the incubator a day or two before setting the eggs. This means placing warm water in the tray for proper humidity and turning on the heat. Correct operating temperature is 101°F. at the top the eggs. This should give ample time to make the necessary adjustments in order to maintain the desired temperature. Make certain that the sides and top of your incubator fit securely so that there is not heat loss! Incubator temperature should be maintained between 100° and 101°F. The acceptable range is 97° to 103°F. If the temperature stays at either extreme for several days, the hatch may not be as good as expected. Overheating is more critical than underheat­ing. Running the incubator at 105°F. for 30 minutes will seriously affect the embryos, but running it at 90°F. for as long as 3 or 4 hours will only slow their metabolic rate. Adjustments may be necessary before reaching a propel

A ~

B

c

16"

FRONT

Sketch No

Sketch No 4

(BACK VIEW)

Sketch No 7

B

THE INCUBATOR - PIECE BY PIECE

.,. ... B

A

D

BACK

Sketch No 2

Sketch No 5

Lamp Base

A or B

E or F i:: :·::;:;::·:::::::. "':: . .-~ "":.-:.-

c SIDE

Sketch No 3

(EGG TRAY)

Sketch No 6

D

rT Incubator Woll

M1crosw1 tch Thermostat Wafer

~m\p\Cord Solderless Connector '\ l.J.

(HEATING UNIT) Sketch No. 8 Mole Electric Plug

(You may prefer to write to Lyon Electric Co., P.O. Box 81303, San Diego, Calif., 92138 for ~ ln_!?rmatlon on Midget Incubator Kit and use It In place of the above heating unit). ~·Ir

6

Assembly The assembly instructions are simple and the lettered 7. Fasten back piece 0 to ends A and B flush with

sketches help to hasten the completion of the unit. top of ends. Attach metal door catch to piece 0 so 1. Attach end pieces A and B to bottom C by screws that when pivoted it will hold door closed.

through bottom. Sketch 1 2. Fasten back piece D to bottom C and ends A and B.

Sketch 2 3. Fasten tray slides E and F to inside surface of ends

A and B level with top of back piece D. Sketch 3 4. Fasten inner front trim G and Hand inner top trim

I and J to ends A and B 7/8 inch from edge. Sketch 4

5. Install glass front light Q. Fasten by attaching front outer trim pieces K and L. Sketch 5

6. Install glass top piece R. Protect glass edge by application of strip of electrical tape. Fasten light by attaching outer trim pieces Mand N.

Material and Parts List

8. Attach door piece P with hinges. Sketch 7

9. Assemble egg try by fastening sides to ends T and U with screws through sides V and W. Fasten hardware cloth to bottom. Sketch 6

10.

11.

12. 13.

Drill a% inch hold one inch from bottom of end A. Drill a % inch hole 2 inches from top of end B. These are ventilation holes. Attach buttons X and Y on outside of ends so they may be used to cover or partially cover ventilation holes. Install the heating unit. Sketch 8. Apply two coats of varnish, inside and out.

The material and parts list for the incubator contains the following items:

1 pc 1/2" plywood 1 pc 1/2" 1 pc 1/2" " 1 pc 1/2" " 1 pc 1/2" 1 pc 1/2" 2 pcs 1/2" quarter round 2 pcs 1/2" " 2 pcs 1/2" " " 2 pcs 1/2" " " 2 pcs 1/2" " " 1 pc 3/16"window glass 1 pc 3/16"window glass

2 Hinges 1 1/2" minimum with 1/2" screws Metal door catch - pivot type

Material List 12"x14" End 12"x14" End 12"x16" Bottom

2 1/2"x16" Back 8"x16" Door 4"x16" Back

10" Tray Slides 10" Inner Front Trim 13" Inner Top Trim 10 1/2" Outer Front Trim 12 1/2" Outer Top Trim

13 1/2"x14 3/4" Front Lights 11 1/2"x14 3/4" Top Lights

1 pkg. 3/4" brads or nails 2 1/2 dz. flat head wood screws #7x1 1/4" long 1 pint spar varnish

1 pc. electrician's tape 10" long

1 pc 1/2" hardware cloth - 10x15" Tray bottom Part S 2 pcs 3/4"x2"x9" Tray ends " T and U

Part

"

" "

Part

"

" "

2 pcs 1/2" plywood 2"x14 5/8" Tray slides Part V and W 2 pcs 1/2" plywood 1"x2" Ventilator Buttons Part Xx Y 1 cake or pie pan 8" round or square-to be used as a water pan doing incubation

Parts List

A B c D p 0 E and F Gand H I " J K " L M " N Q R

1 pc No. 14 lamp cord 6' long 1 male electric plug 1 micro switch, holder, and the thermostat wafer of the type used in chicken brooders - obtainable from

hatcheries, mail order houses, farm supply stores, and incubator sources listed on page 5. 2 flat base porcelain lamp sockets with attachment screws 2 75 watt light bulbs 1 pc No. 14 plastic coated wire 5' long 2 solderless connectors 1 small alcohol thermometer 1 pc stiff cardboard 4 "x6"

7

Incubation Record Chart

Date Time eggs are turned

Room temp.

Incubator temp.

setting. The unit is now ready to begin with the hatching process. Certain practices need to be observed.

1. Mark all eggs with a pencil. One way to mark the eggs to help you keep track of how they have been turned is to write the date on one side of each egg with a pencil. The date when the egg is placed in the incubator should be used: 8/10, for instance. Or you can use just a pencil line instead of the date.

Place the eggs on the welded wire platform horizon­tally, in a single layer, with the dates (or lines) on top. When the eggs are turned. all of the dates will be on the bottom or out of sight. At the next turning, the dates will be in view, and so on.

2. Place eggs on tray, laying them on their sides. Turning the eggs during the incubation period prevents the eblastoderm from migrating through the albumen and sticking to the shell membrane. When turning eggs, move them to different parts of the tray. This is done to take care of any variation in temperature that may occur. The eggs should be turned three to five times daily from the 2nd to the 19th day. Do not turn the eggs during the last 3 days!

Remarks (who turned eggs, etc.)

Near the incubator, post a chart on which records can be kept. The person who turns the eggs can observe and record other information to help keep track of the incu­bation and hatching schedule (see example chart. p. 8).

When incubators are used in schools, it may be dif­ficult to turn the eggs on weekends. If the eggs are not turned, the hatch may be somewhat lower. but this should not interfere seriously with the success of the project.

Except for the 19- to 21- day period, it is safe to move the incubator with the eggs in it. In some schools. the temperature is reduced on weekends and holidays, and it may be advisable to take the incubator home. Rolling and cracking can be prevented during the move by pack­ing crumpled paper around the eggs. The incubator should be wrapped in a heavy blanket and placed in a warm car to maintain the temperature of the eggs. and the trip should not take more than half an hour.

After the 18th day, do not open or move the incubator until the hatch is completed because the chicks are in a hatching position in the eggs and because a desirable hatching humidity must be maintained.

Symptom Incubation Troubleshooter

Probable Cause

Chicks hatching too early, with bloody navels.

Draggy hatch: some chicks early but slow in finishing.

Delayed hatch: eggs not pipping until 21st day or later.

Short down on chicks.

Mushy chicks. Dead on platform. Bad odor.

Chicks too small.

Shell sticking to chicks.

Chicks smeared with egg contents.

Crippled chicks: missing eye, cross beak, extra leg, etc.

Rough navels.

8

Incubator temperature is too high.

Temperature too high.

Temperature in incubator is too low.

High temperature or low humidity.

Naval infection caused by bacteria in incubator.

Low humidity or high temperatures.

Low humidity at hatching time.

Low average temperature. Humidity may be too high.

Mostly chance. Poor nutrition of parent stock. Heredity.

High temperature or low humidity.

3. Hatching Failures. Chicks fail to hatch for a number of reasons. Ordinary handling does not hurt the egg due to the protection of the embryo of the amniotic fluid. Excessive handling and jarring of the hatching egg may be harmful. The incubation temperature needs to be correctly maintained, and it has to be kept as nearly constant as possible. Too little humidity in the incubator is a serious matter, especially at hatch time. Excess mois­ture is better than too little moisture.

Some chicks will fail to hatch due to inherent weak­ness. This is natural and in a way it is nature's way of weeding out the weak. Weakness of the chick may be due to the improper nourishment of the parent stock. This is why proper and correct nutrition is a must for all - be it bird, or mammal. If the eggs are not held under proper temperature and humidity before incubation, the hatch may prove disappointing.

It is always best to follow the instrucitons given for the kind of incubator being used in order to obtain satisfac­tory results. After the 21st day, if some eggs are pipped but not yet hatched, adding boiling hot water to the moisture pan to "steam up" the incubator may help some of the chicks to hatch.

One should expect a hatch of 50 per cent, or better if 9 5 per cent of all the eggs placed in the incubator are fertile. Chicken eggs require 21 days to hatch, turkeys 28 days, most duck eggs 28 days, geese 30 days, pheasant 23-24 days and pigeons 17 days.

Albumen Yolk sac

5DAYS

Albumen

15 DAYS

Cleaning the Incubator. When the hatch is completed the incubator should be disconnected. The chicks, shells, and unhatched eggs should be removed and in­terior wiped clean with a soapy sponge. It should be permitted to air dry for several days by permitting the door to remain open. The incubator will then be ready for use or storage.

CHICK EMBRYO DEVELOPMENT

Where Chick Life Begins

The life of the chick begins in the single cell formed by the union of two parental cells, egg and sperm, in the process known as fertilization. In birds, fertilization oc­curs about 24 hours before the egg is laid.

The newly formed single cell begins to divide into 2, then 4, 8, 16, 32, and more cells. At the time of laying, hundreds of cells are grouped in a small, whitish spot (the blastoderm) which is easily seen on the upper sur­face of the yolk. This spot in a fertilized, freshly laid egg is the beginning of the chick. (See figure 1, page 3.)

When the egg is laid and cools, division of the cells ceases. Cooling the egg at ordinary temperatures does not result in the death of the embryo. It may resume its development after several days of rest if it is again heated by the hen or in an incubator.

Allantois

Albumen

Allantois

10 DAYS

20 DAYS

Yolk sac

Egg tooth

Figure 4: Successive changes in the position of the chick embryo and its membranes. 9

Development During Incubation

As soon as the egg is heated agam the cluster of cells m the blastoderm begins to multiply by successive divi­sions The fust cells formed are all alike. Then, as the division of cells progresses. some differences begrn to appear.

These differences become more and more pro­nounced Gradually the various parts of the duster of cells acqmre specific characteristics of structure and cell grouping. These new groupings of cells start to serve the rest of the cluster in their own ways. They become indi­vidual tissues and organs, and the whole cluster, con­sisting of many millions of cells, becomes a new or­gamsm

Development from a srngle cell to a fully developed chick is a continuous, orderly process It involves many

Table 1. Important Events in Embryonic Development

Before egg-laving

Between laying and 1ncubat1on

During incubation First day

16 hours

18 hours 20 hours 21 hours 22 hours 23 hours

24 hours

Second day 25 hours 35 hours 42 hours

Third day 50 hours 60 hours 62 hours 64 hours 70 hours

Fourth day Fifth day

Sixth day

Eighth day Tenth day Thirteenth day Fourteenth day

S1 xteenth day

Seventeenth day Nineteenth day Twentieth day

Twenty-first day

Fert1l1zat1on D1v1s1on and growth of living cells Segregation of cells into groups of special function

No growth, stage of inactive embryonic life

First sign of resemblance to a chick embryo

Appearance of alimentary tract Appearance of vertebral column Begmnmg of formation of nervous system Beginning of formation of head Appearance of blood islands - v1telline

circulation Beginning of formation of eye

Beginning of formation of heart Beginning of formation of ear Heart begins to beat

Begmrnng of formation of amnion Beginning of formation of nose Beginning of formation of legs Beginning of formation of wings Beginning of formation of allanto1s

Beginning of formation of tongue Formation of reproductive organs and

different1at1on of sex Beginning of formation of beak and

egg-tooth Beginning of formation of feathers Beginning of hardening of beak Appearance of scales and claws Embryo turns its head toward the

blunt end of egg Scales, claws, and beak becoming firm

and horny Beak turns toward air cell Yolk sac begins to enter body cavity Yolk sac completely drawn mto body

cavity Embryo occupies practically all the

spacew1thm the egg except the a1rcell

Hatching of chick

10

changes from seemmgly simple to new, complex struc­tures From these structures arise all the organs and tissues of the hvmg chick (See table 1.)

Physiological Processes Within the Egg

Many elaborate phys10logical processes take place durrng the transformation of the early embryo to the chick. These processes are: utilization by the developing embryo of highly nutritious food materials from the egg; respiration of gases - takmg in oxygen and expelling carbon dioxide; and buildmg up of living structures within the chick

Function of the Extra-Embryonic Membranes

Special temporary organs or embryonic membranes are formed withm the egg, both to protect the embryo and to provide for its nutrition, respiration, and excre­tion. These organs include the yolk sac which covers the yolk of the egg, amnion, and allantois. (See figure 4.)

The yolk sac membrane transports food material to the embryo The amnion, by enclosing the embryo, provides protection The allantois serves as a respiratory organ and as a reserv01r for the excreta. These temporary or­gans function within the egg until the time of hatching, and do not form any part of the fully developed chick.

Function of the Embryonic Blood Vessels

During the incubation period of the chick, there are two sets of embryonic blood vessels. One set, the vitel­line vessels, is concerned with carrying the yolk materi­als to the growing embryo. The other set, the allantoic vessels, is chiefly concerned with respiration and with carrying waste products from the embryo to the allan­tois. (See figure 5.) When the chick is hatched, these embryonic blood vessels cease to function.

Allanto1s

V1tetl1ne vessels

Figure 5. Seven-day-old embryo with its embryonic mem­branes and embryonic blood vessels.

Seoveral changes to during the 17th to 19th The amount of de-croas;s in the amnion The chick's neck acquires a dou­b"le bend so that its beak is under its right \dng toward the air chamber The remaining yolk sac is re-tracted into the cavity for use as after the hatches.

On the 2oth day the chick thrusts its head forward. Its beak rapidly pierces the membranes. enters the air cell. The chick begins slowly to breathe the air ihat diffuses into the cell and may be heard to peep within the shell.

On the 21st day the "escape" of the chick from its "prison" begins. The first break in the shell is made by the egg tooth, a sharp horny structure located near the tip of the upper beak. The pipping chick begins to breath normally The allantois dries up and circulation to 1t

rapidly ceases The process of hatching is accomplished by the chick

as it slowly revolves in the shell and chips a circular path around it. Then, a vigorous twist of the chick's neck makes the shell walls crack, and the shell falls open along the chipped path. Freedom is gained.

But the chick is still wet, and for a while it seems exhausted and helpless. Not until a few hours later can the chick, now dry and fluffy. take full advantage of its freedom and wander about in its new and mysterious world.

Although used only for a single event in the life of the chick, as a tool to chip through the shell, the egg tooth has served its critical purpose well. Its usefulness over, it will be lost in a few days.

The yolk material, about one-sixth of the chick's weight, will soon be used. This built-in provision of food helps tide the chick over a day or two until it learns to eat and drink on its own.

mav kept for display and study if proper care fadlities are

to protect, dnd \\ ater them to ensure their comfort. Remember to find a home for the

it is to suffer and die

Although there is no definite of brooding. a maximum of 10 days is probably enough to garn insights mto the chicks bPhav10r, edting habits, rte.

Equipment and Supplies for Brooding 12 Chicks

Cardboard box approximately 28'' x 25" x 14". (each chick should have about 36 square inches of space, though slightlv less room per chick is acceptable for a short while.)

A wood box may preferable to cardboard if other animals are around and will have access to the broader. Wood is more stable, less easily chewed through. Welded wire cover for brooder -%-inch to 1/2-inch mesh is best to protect chicks from cats or other animals.

Gooseneck lamp with a 60- to 75-watt bulb to keep the chicks warm.

Shavings, straw, peat moss. or other appropriate litter material.

Feed tray.

Water fountain.

Procedure

Feed - chicken starter. (contact local feedmill.) Pebbles, marbles, or 1/4-inch screen.

A simple brooding unit may be used to keep a few chicks for a short time. The principles of brooding are the same regardless of the number of chicks in the flock. Whether there are 2 chicks in the brooding unit or 2 ,000, they have to be kept warm, well fed, and watered; pro­tected from predators and dampness; and provided with plenty of fresh air without being exposed to drafts. The unit described here, when used in a warm place such as a schoolroom or at home, will do the job.

Figure 6 shows a box of the sort to be used as a brooder house for the chicks. The shape is not important as long as it is large enough to house the chicks adequately and contains the equipment (water fountain. food, and litter material) to care for the chicks. A gooseneck lamp next to the box can provide heat.

Chicks must be able to get away from direct heat, so having the lamp at one end with slightly cooler area at the other end of the box is advisable. If the side of the bo:x: is very high, a slot can be made so that the base of the lamp can be placed outside while the gooseneck fjts th:rough the $lot an.cl ther shade a'.lld bulb are i:r;i,~:jd~ the

box BP sure that such an heat !fl t!w bu' ton rnll'HS«

i\ hO- to 7:i-P. <itt bulb \\ armlh. The ned. of the bulb closer to the chicks if

floor ar<>a of the broodrng unit.

Ideal Age of Chicks 1 day to 1 week 1 week to 2 weeks 2 weeks to 3 weeks 3 weeks to 4 weeks 4 weeks to 5 weeks

Temperature 95°f B0°F 85°F 80°F 75°F

Each brooder unit should contain at least one waterer and one feeder. Place the waterer on a vvooden block or stand to help keep the litter dry. Chicks should be able to dip only their beaks into vvater dish. so place pebbles, marbles, or a screen in the dish. Wet chicks are much more susceptible to drafts and disease. Chick starter can be obtained from a feed dealer. As a temporary measurer. if starter is not available, some of the new high-protein. -vitamin, and -mineral dry cereals for human beings can be crushed and fed to the chicks Feed and water the chicks as soon as they are moved from the incubator to the brooder.

The litter in the brooder serves as insulation and as an absorptive material. Peat moss, wood shavings, saw dust. straw, or sand can be used. Never place young birds on a smooth surface because they cannot grip a slippery surface - their toes curl, and their legs spread out to the side. This may result in permanent leg dam­age.

The walls of the brooder serve as a chick guard and keep drafts off the chicks. After the chicks have been put into the brooding unit. cover it with a welded-wire screen. This will keep the chicks in, and predators such as cats out. A mesh which is too large will still allow chicks to slip through or a cat to reach in - 1/z-inch welded wire or hardware cloth is probably the most satisfactory size to use.

Remember, all domestic animals depend on human beings for survival. Make sure the chicks are properly housed, kept warm and out of drafts, and have food and water. This means checking the brooder morning, noon. and night (just before going to bed). In the classroom, check first thing in the morning, at noon, and at the end of the day.

What to Do With the Chicks When the Project is Over

Before beginning an embryology and incubation pro­ject, you must make a decision Oil a proper and humane way of dealing wi~h the chio:ks whe:n the project is ove:i;. If you cannot find a new hmne for the obieks where they

12

l Give them to someone who has brooding fac1hties, some successful experience. an interest in car-

properly for the chicks, and the ability to deal with grown chickens. A local farmer or poultry grower may be 'INilling to take the chicks.

2 Contact the local S.P.C.A or human society In most instances they will dispose of the chicks for you, or locate someone to provide care for them. There may be a charge ±or this service. The S.P.C.A. is listed in most phone books

Helpful Literature A pro1ect outline serves primarily as a guide for the

student \'\rho needs a road map for a charted course. The student with an inquisitive mind will find a whole panorama of scientific information available at a public library. The following helpful publications relating to poultry and to embryology may be found in school li­braries, or school librarians can obtain the publications for the student:

l. The Chick Embryo in Biological Research, Annu­als of the New York Academy of Sciences. Vol. 55 (2), 1952.

2. An Introduction to Embryology, Balinsky. BJ .. W.B. Saunders Co .. Philadelphia.

3. Introduction to Vertebrate Embryology, Waldo Shumway, 4th Edition, John Wiley & Sons, New York.

4. The A vi an Egg, Alexis Romanoff and Anastasia Romanoff, John Wiley & Sons, New York.

5. The Avian Embryo, Alexis Romanoff, The MacMil­lan Co., New York.

6. Lillie's Development of the Chick, revised by H. L. Hamilton, Henry Holt Co., New York.

7. Life Magazine, December 7, 1959 issue, See Page 76-80.

8. Science Studies in Poultry Biology, Poultry Sci­ence Association, Inc., 113 N. Neil Street, Cham­paign, Illinois 61820. (Reprinted from Poultry Sci­ence, Vol. 53, 1974.)

Other Poultry Science Experiments For other e:x:perime:nts, ideas and suggestiQ.,ns, please

write to The Poultry Sc~ence DepartlP+e:t;lt, The Ohio State Univer!>ity, 674 West 4ana A.ven~~. Coltill1bus, Ohio 43210.