Head over Tiels
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HOW DOES AN EGG BECOME A BIRD?
OVULATION:The female parrot has only one mature ovary. It is on the left side of her body. The right ovary is underdeveloped and does not function.
HEN REPRODUCTIVE SYSTEM: Yolk protein and lipids or fats are manufactured in the liver and travel in the bloodstream to the occyte, the immature ovum, during the maturation stage. Excellent nutrition including vitamin E and selenium result in the components of the egg also being superior. Disease can be transmitted through the ovary to the ovum. Although only one ovum matures at a time, the hen is born with a finite number of ova. Ovulation, the shedding of an egg from the ovarian follicle, occurs when the brain's pituitary gland releases a lutenizing hormone, LH. Mature follicles form a stalk or pedicle of connective tissue and smooth muscle. The mature ovum erupts from its sac and starts its journey through the oviduct, the organs from the ovaries to the vent. Immediately after ovulation the follicle becomes a thin-walled sac, the post-ovulatory follicle, which in the chicken regresses in about ten days. It is likely that the post-ovulatory follicle secretes hormones, perhaps progesterone, affecting oviposition or egg laying as well as nesting behavior. During a molt, ovulation ceases and the follicles are absorbed.
FERTILIZATION / INFUNDIBULUM:The ovum enters the infundibulum where fertilization occurs. The infundibulum acts as a catcher's mitt. Internal laying is where the infundibulum fails to grasp the ovum and it is then lost in the coelom or body cavity. Many are harmlessly absorbed while others are involved in egg peritonitis, an inflammation of the membrane lining the abdominal cavity.
The ovum is fertilized within fifteen minutes of ovulation. This must occur before the ovum becomes covered by albumen. The smooth muscle layers in the vagina and uterus rapidly transport spermatozoa up the oviduct by oviductal retro peristalsis, wavelike circular contractions. These circular contractions also drive the egg downward by peristaltic waves. The sperm penetrates the blastodisc, the nucleus of the egg. This blastodisc is a small white spot on the top side of the yolk. When the sperm lodges within this germinal disc, an embryo begins to form. It is now known as a blastoderm or zygote. The fertilized ovum continues down the path toward the vent in the next 24 hours. In birds the female carries the XY combination which determines the sex of chicks. This is opposite from mammals.
MAGNUM:During the approximately three-hour stay in the magnum egg white is added to the ovum. Egg white is a protein substance containing mucus, globulin and albumen including sodium, magnesium and calcium.
ISTHMUS:During the approximately 75 minute stay in the isthmus another 10 percent of the albumen, the chalazae and membrane are added to the ovum. A thick egg white is added called the chalazae. The chalazae are little ropes which hold the yolk in the center of the egg. They surround the yolk and attach at polar ends of the egg to permit the yolk to rotate so the blastoderm stays on top. At the small end of the egg the chalazae is a double strand and at the large end it is a single strand. As the egg progresses it is rotated by the folds within the oviduct which are continuous and form a spiral. There are about 22 very well developed primary mucosal folds with no secondary folds. There are finally two membranes formed. They are joined except in the area where the air cell will be, where they will separate. The larger the bird, the thicker the shell will be. The smaller the bird and the thinner the shell and the thicker the membrane will be.
UTERUS:The egg will spend 20 hours in the uterus, a thick-walled muscular area. Here, water and salts which plump out the egg are added through the membranes. And finally, the shell will be added to the egg. The shell and pigmentation are produced by glands in the walls of the uterus. Blue-green shell pigment is biliverdin and red-brown pigment is porphyrins. All parrot eggs, however, are white. Shell has three layers. The inner layer which is the first produced is called the mammillary layer. The middle layer is the testa which is the thickest layer. Last produced is the outermost layer made of dried mucous. There are more pores in the smaller end of the shell, and the first egg in a clutch tends to have a thicker shell than the rest. Parrot shells are thinner and more pliable than those of other birds. Parrot embryos do not absorb calcium from the shell. Therefore, the cuticle deposited over the shell of other types of birds is not applied. Parrots develop their strong supportive skeleton after hatching and calcium then becomes an important dietary requirement. Calcium for formation of shell comes from two sources: diet and the medullary bone. This bone is a cancellous, spongy, porous or lattice structured bone laid down in the marrow cavity of the long bones about two weeks before the onset of laying. During the laying cycle this bone is periodically produced and reabsorbed. Incubation begins in the uterus where the first cells divide.
VAGINA:The egg stays in the vagina for only a few seconds. Nothing is added to the egg here. The soft egg is shaped in the vagina relative to the shape of the bony pelvis. A spherical egg is shaped when the pelvis is deep dorsoventrally, extending from the dorsal or back to the ventral, the belly or lower side. An elongated egg is shaped when the pelvis is narrow dorsoventrally. Other shapes are known as pyriform or pear shaped, ovate or egg shaped, elliptical or having both ends equally sized, short, long and pointed. The size of an egg depends on the size of the yolk. Yolk size is, of course, relative to the size of the species. When first laid, an egg's temperature is the same as that of the hen. As the egg cools, its contents lose volume. The shell density changes slightly, creating a negative partial pressure which draws air into the egg and forms the air cell. Contaminates can be pulled into the egg at this time. At the time an egg is laid, the embryo already consists of more than 20,000 cells. The egg is still soft as it is laid. As it cools and dries, the shell hardens. Parrots are determinate layers which mean they lay a fixed number of eggs in each clutch. Indeterminate layers can be induced to lay as many as 365 eggs a year by removing each egg laid. These species are commonly seen in production of eggs for food.
EMBRYO DEVELOPMENT:Incubation tolerances in parrots are more critical than in other species such as chickens. Parrot eggs incubate in 18 to 29 days depending upon the species. About 15% of an egg's original weight is lost due to evaporation during the incubation process. Eggs incubate at 99.1 to 99.5 degrees Fahrenheit with humidity between 50 and 53%. During brooding the temperature of the brood spot rises. The brood spot is where a large supply of blood collects. Its location varies depending upon species. A brood spot can be found on both hen and cock depending upon species.
The egg, which is a balanced combination of protein, carbohydrates, minerals, vitamins, fats and water become the nutrients which nourish and protect the developing chick until it hatches. The embryo floats in a sac filled with clear amniotic fluid which surrounds and protects it. The chick swallows the clear protein rich fluid. The blood system supplies the embryo with food from the yolk and albumen. It exchanges oxygen for carbon dioxide through the pores of the shell. Fat is the major component of membranes. The chick grows a lot of cells, each surrounded by membrane. Fat can be oxidized to carbon dioxide and water to provide energy to support the growth of the chick. Egg membranes are amnion, chorion and allantois. They are sheets of living tissue which grow out of the embryo itself. A pouch-like outgrowth of the digestive system grows around the yolk to form the yolk sac. The yolk sac will be taken into the belly or abdomen of the chick completely before hatching. The chick will use the yolk as food for several days after it hatches. The amnion and chorion develop as folds of the body wall and surround the embryo. The amnion develops into a fluid filled sac in which the embryo grows allowing movement. The allantois, an extension of the digestive tract, fuses with the chorion to form a compound membrane, the chorioallantoic membrane or CAM.
Chronology by day of the development of a chicken egg:1. Cells have started to form the digestive system, head, eyes and nerves. 2. A circle of red streaks, which are the beginnings of the circulatory system or blood stream, form on the surface of the yolk. The embryo develops in the center of this circle. The heart forms and begins to beat. 3. More blood vessels develop and cover more of the yolk surface. Legs, wings and tail begin to form. 4. Brain is developing. 5. Faint segments along the back indicate where back bones or vertebrae will form. 6. Circulatory system covers ½ the yolk. 7. Head is about the size of the rest of the body. Beak is forming the egg tooth. 8. Head and beak are well formed. 9. Toes are seen. A foundation for feather development is forming. 10. Eyelid begins to cover eye. Body begins to grow faster. 11. Weight has doubled in two days. Weight will double again in two days. Ear opening can be seen. Blood vessels are under the skin. Skin has texture indicating where feathers will grow. Bones in the eyes, top of skull and toe joints are visible. 12. Feathers are evident in tail region. Scales and claws form. Eyelid nearly covers eye. 13. Feathers cover most of embryo. Head turns toward large end of egg. Eyelid totally covers eye. 14. Proportions of head, body and limbs are balancing. 15. Embryo needs more oxygen. Most of the albumen has been used up. 16. Yolk decreases in size. Head turns so beak is under right wing. Beak, claws and scales are hardening. 17. Eyelid is closed. Toes are distinct and feathers are well developed. 18. Chick prepares for hatching in final stages.
HATCHING:Hatching is triggered by a buildup of carbon dioxide in the embryo due to an inability of the circulation of the allantois to meet the gaseous exchange needs of the embryo. Increased carbon dioxide levels cause the neck muscles to twitch. If the embryo is properly positioned, this twitching motion will cause the egg tooth to penetrate the CAM and move into the air cell. Malposition of the embryo is greater than one in ten, therefore creating a situation where the chick tries to hatch from the wrong side of the egg. The small bubble of air in the large end of the egg is called the air cell. Water is lost to evaporation during incubation which increases the size of the air cell. The air cell is separated from the embryo by a thin shell membrane. As the chick begins to breathe, the lungs start to function and the right-to-left shunt in the heart, which allows blood to bypass the lungs, closes. The twitching of abdominal muscles draws the yolk sac into the abdomen. When the chick begins breathing in the air cell, one can hear an internal clicking noise caused by the moist respiratory tubes sticking and pulling apart. As the chick breathes air contained in the air cell, the carbon dioxide content rises to approximately 10 percent. This again induces neck twitching which causes the egg tooth to penetrate the shell. This is called pipping. The length of time from internal pipping to hatching is 24 to 72 hours. The length of time from external pipping to hatching can happen very quickly. Chicks hatch at 97.5 to 98.5 degrees with humidity at 80%. Temperatures lower than 97 or higher than 102 degrees will cause the chick to die. From pipping onward, eggs give off ammonia and carbon dioxide. It is unwise to keep a hatching egg with developing eggs due to this emission of toxicity as well as the changed temperature and humidity requirements. As the chick hatches there is an alternation between the jerking head movements and contractions of the head and neck muscles which forces the chick to rotate slightly counterclockwise. The chick uses its right wing as a guide for pipping the path forming the cap through which it will escape. The albumen acts as a lubricant that helps the chick turn, push and struggle to free itself at hatching. Albumen is rich in anti-bacterial lipozymes which is fat soluble and causes fermentation. Soon after hatching, the egg tooth drops off. Parrots are known as altricial. This means a bird which hatches helpless, eyes closed and often naked. Birds which hatch covered in down with eyes open and capable of moving around are called precocial.
Chronology by day of the development of a chicken egg:19. Chick fills egg except for air cell. Waste products have accumulated. 20. Yolk sac withdraws into abdomen. Navel will close and heal once the yolk sac fully retracts. Chick pierces air cell and breathes in the air cell. The allantois will no longer carry enough oxygen to chick. 21. Pipped. Kicks to turn its body inside shell. Pecks circular path around top of egg. Top will be pushed off. Other animals which hatch from eggs are lizards, snakes, frogs, fish, insects and turtles.
References:1. Richard M. Schubot, Kevin J. Clubb and Susan L. Clubb DVM - Psittacine Aviculture Perspectives Techniques and Research - Willis Printing Group, Inc., 1992. 2. John McLelland BVMS, MVSc, PhD, MRCVS - A color Atlas of Avian Anatomy - W. B. Saunders Company, 1991. 3. Tony Silva - Psittaculture Breeding, Rearing and Management of Parrots - Silvio Mattacchione & Co., 1991. 4. A. S. King BSc, PhD, MRCVS and J. McLelland BVMS, MVSc, PhD, MRCVS - Birds their structure and function Second Edition - Bailliere Tindall, 1984. 5. A. L. Cartwright Poultry Science Department Texas Agricultural Extension Service, Texas A. & M. University - The Egg and Embryo Life Science Series, Chicken Embryo Development. 6. Janet Stromberg - A Guide to Better Hatching - Stromberg Publishing Company, 1975. 7. Matthew M. Vriends - Simon & Schuster's Guide to Pet Birds, 1984. 8. Rick Jordan - Parrot Incubation Procedures - Silvio Mattacchione and Co., 1989. 9. The American College Dictionary - Random House, 1966. 10. Webster's Seventh New Collegiate Dictionary - G. & C. Merriam Company 1963. |
Within minutes of insemination, the depositing of sperm from the cock's ductus
deferens into the hen's vent during breeding, the sperm reach the top of the
oviduct, but within twenty-four hours they disappear. Sperm reappear in small
numbers at the time of subsequent ovulation. In the region of the sphincter the
tubular spermatic fossulae or sperm-host glands are the main sites for the
storage of spermatozoa. 