Technology and organization of industrial incubation of poultry eggs

Incubation has gained industrial importance due to the specialization and intensification of poultry farming and is successfully carried out throughout all months of the year. Year-round incubation eliminates the seasonality of poultry reproduction and creates prerequisites for the continuous growth of egg and meat production. It allows for the production of large batches of same-age young stock for rearing and improves the quality of poultry.

At poultry farms, hatchery-poultry stations, and specialized state poultry farms in our country, egg incubation and the hatching of young stock are carried out on a large scale. In the USSR as a whole, more than 2 billion eggs are placed in incubators annually, and approximately 1.6—1.8 billion heads of young poultry of all species are hatched. According to the perspective plan of the USSR Poultry Industry, it is planned to place 3.5 billion eggs into the country's incubators in 1980.

All poultry farms in the country possess a large number of incubators, the one-time capacity of which is 400 million egg spaces. In the large incubation departments of poultry farms, up to 5—6 million chicks are hatched annually for the replacement of flocks of caged laying hens. The incubation of eggs from meat-type breeds of chickens, ducks, turkeys, geese, and guinea fowl is expanding. The hatchability of young stock in incubators across the country as a whole is 78—80%. However, there are many good farms where the hatchability percentage is 85 or higher.

Incubation technology is based on knowledge of the biology of embryonic development of farm poultry in relation to its species and genetic characteristics under controlled environmental conditions. This is utilized in the design of incubators, methods for selecting incubation eggs based on quality, the incubation regimen, etc. Incubation technology includes the use of incubation eggs as starting material, the hatching of day-old purebred and hybrid young stock, and its transfer to farms.

The technological process of incubation consists of individual operations:

• selection of eggs for placement in the incubator;
• creation of a scientifically grounded incubation regimen;
• sorting and sexing of young stock;
• marking of young stock, etc.

Incubation technology is implemented in farms with a closed production cycle, for example, at a poultry farm. Here, the work of the incubation department is most closely linked to the activities of the parent flock department and the young stock rearing department. The technological process at a hatchery-poultry station has a different basis; it depends on the quantity and quality of eggs arriving there from collective and state farm farms, and on the hatching of young stock both for these farms and for sale to the public.

With further specialization and concentration of production based on inter-farm cooperation, the technological process of incubation requires improvement. For example, when using cabinet incubators or hatching young poultry in large batches, it is necessary to develop new incubation schemes. However, in any case, consistency in work, interconnectedness, continuity, and rhythmicity of production processes are maintained.

Breeding flock of 15,000 hens, 3,000,000 eggs.

Fig. 44. Scheme of the technological process for hatching 2 million chicks.

Currently, incubation is understood not only as the hatching of young poultry but also as the management of the process of growth and development of embryos. The main point is to increase viability and ensure better development of embryos through appropriate selection of high-quality eggs, correct technology, and incubation regime. The embryonic period in birds takes very little time; for chickens, for example, about 0.2% of their lifespan. But the period of embryogenesis is of great importance in the entire process of individual development of the organism.

The development of the embryo begins during the formation of the egg in the bird's body. However, it mainly takes place in the egg after it is laid upon being placed in an incubator. For its growth and development, the embryo uses the nutrients of the egg, which also contains a reserve of water that ensures metabolism during almost the entire incubation period. Only oxygen reaches the developing embryo from the surrounding air. Improving incubators, increasing their utilization rate, improving the technological process, and mechanization and automation of individual operations are the most important factors in the technical progress of industrial incubation.

The essence of fertilization consists in the fusion and mutual assimilation of the nucleus of one of the sperms with the nucleus of the female cell. During fertilization, only one nucleus of the male cell joins with the nucleus of the female cell.

Currently, more and more data are being accumulated indicating how important the presence of a large number of sperms in the bird's reproductive organs is for obtaining the greatest number of fertilized eggs. Although one sperm fertilizes the ovum, the rest (20—60) remain in its protoplasm and, obviously, are of importance for the subsequent viability and development of the embryo. A fertilized ovum is called a zygote; it contains particles from both the paternal and maternal organism, that is, double heredity. In practical work, it is necessary to take into account that in highly productive poultry, for example with an egg production of 250—300 eggs per hen, less time is spent on follicle maturation in the ovary and on the formati No: Fig. 45. Schematic longitudinal section of a chicken egg in a horizontal position. The embryo is sectioned transversely (according to M. N. Ragozina). Age — one day from the start of incubation:

four days from the start of incubation. The designations are the same as in Figure 45:

1 — shell; 2 — shell membrane; 3 — vitelline membrane; 4 — albumen membrane; 5 — chalazae; 6 — yolk; 7 — egg air cell; 8 — ectoderm; 9 — mesoderm; 10 — endoderm. 66 — thick layer of yolk: 8a — ectoderm of the yolk sac; 8b — ectoderm of the serosa; 8v — ectoderm of the amnion; 9a — mesoderm of the yolk sac; 9b — mesoderm of the serosa; 9v — mesoderm of the amnion; 9g — mesoderm of the allantois; 10a — endoderm of the yolk sac; 10b — endoderm of the allantois.

on of the egg in the oviduct than in less productive layers. To obtain more fertilized eggs, the parent flock is provided with complete feeding, good housing conditions, and the correct ratio of males and females in the flock is established.

Development of the embryo during the egg formation process. 3—4 hours after fertilization, the zygote begins to divide. Cleavage furrows appear on the surface of the germinal disc, which separate the blastomeres from each other. Before the egg is laid by the bird, there are 128 primary cells in the germinal disc. A cavity filled with transparent liquid appears under the central part of the cleavage zone. The center of the disc becomes lighter and is called the area pellucida. The peripheral part of the disc, or area opaca, consists of blastomeres lying on the yolk. The cells of the future embryo are not yet differentiated and do not have the characteristics of any particular tissue. During cleavage, the embryonic cells lie on the yolk or directly on it. They receive nutrients and plastic material from the yolk. From the chemical compounds of the yolk (during their decomposition), the oxygen necessary for cellular respiration is released.

The first period of development of the germinal disc passes in the maternal organism (in the ovary and oviduct of the layer) at the bird's body temperature of about 41°C, a carbon dioxide concentration of up to 5%, and under conditions that exclude water evaporation. Developing intensively and continuously for 22—24 hours during the formation of the egg in the mother's body, the embryo reaches the early gastrula stage. When the egg is formed, the hen lays it. The temperature and humidity of the environment surrounding the egg change sharply, which affects the development of the embryo: all processes of assimilation and dissimilation slow down. But the embryo is alive; it breathes, absorbs nutrients, and excretes metabolic products. At this time, it is very sensitive to environmental conditions, so the task of poultry farmers is to create optimal conditions for the development of embryos both during the storage of eggs before being placed in the hatchery and during incubation.

Embryo development during incubation. The components of an egg are the sole source of nutrients and water for an embryo. The viability, growth, and development of the embryo depend on their ratio and the quality of individual elements. The components of an egg (yolk, albumen, and shell) change in volume, physical state, and chemical composition during incubation. This occurs under the influence of the incubation regime (temperature, relative humidity of the air, air exchange, etc.) and is particularly intense due to the rapid growth and development of the embryo itself.

The formation of an organism day by day during incubation can be traced using the example of chicken embryo development. Information is provided on the periods during which the most significant changes in embryo growth and development occur.

Fig. 47. Embryo at 10 days of age from the start of incubation (after M. N. Ragozina): 1 — embryo; 2 — yolk sac; 3 — allantois; 4 — amnion; 5 — albumen membrane (albumen); 6 — air cell; 7 — shell membrane.

Fig. 48. Embryo at 20 days of age from the start of incubation (after M. N. Ragozina): 1 — part of the yolk sac not retracted into the abdominal cavity; 2 — allantois; 3 — air cell; 4 — shell membrane; 5 — shell.

1st day of incubation. At the beginning of the first day of incubation, the final formation of two germ layers occurs — the ectoderm (upper) and the endoderm (lower). Soon, a third (middle) germ layer forms — the mesoderm. These three layers are called germinal layers. In the future, specific tissues and organs develop from them. The upper layer of the skin and its derivatives form from the ectoderm: in poultry, these include feathers, comb, wattles, beak, claws, nervous tissue, and all sensory organs. The tissues of most of the digestive tract and its glands, respiratory organs, and several endocrine glands (thyroid, thymus, etc.) form from the endoderm. The mesoderm forms muscles, excretory organs, and gonads.

The germinal disc expands on the surface of the yolk. The pellucid area stretches along the minor axis of the egg and has a pear-like shape. Later, the tail part of the embryo develops from the narrow part of the pellucid area, and the head part develops from the wide part.

After 6 hours of incubation, a primitive streak appears in the chicken embryo — a zone of intensified cell division. Where it forms, the upper and lower cell layers of the germinal disc fuse together. By 12 hours of incubation, the primitive streak accounts for half the length of the germinal disc, and by 18 hours, its length is 3/4 of the germinal disc length. The development of the primitive streak is a good indicator for biological control on the first day of incubation. In a well-developed embryo, the maximum diameter of the germinal disc is 0.5 cm. The embryo and yolk are surrounded by the vitelline membrane. A small amount of liquid layer appears on the surface of the yolk, which accumulates under the germinal disc. Already on the first day of incubation, the eccentric position of the yolk is noticeable, as a result of which the germinal disc located on its surface moves closer to the shell membrane.

Formation of a viable embryo: from laying to the seventh day

On the first day of incubation, the foundation for the health of the future livestock is laid. The albumen is distributed unevenly around the yolk, leaving the germinal disc almost exposed. This is necessary for respiration: the yolk shifts closer to the shell, improving gas exchange. By the end of the first day, the head process of the embryo is already differentiated, and the optic vesicles, heart rudiments, as well as the nervous and digestive systems are forming.

On the second day, blood circulation begins. The neural folds close into a tube, about 20–22 pairs of somites form, and the heart begins to beat rhythmically after just 30 hours of development. The vascular system of the yolk sac is located directly under the shell membrane, ensuring oxygen supply. The heart rate during this period depends directly on the temperature in the incubation chamber.

• Start of heart pulsation — 30 hours
• Number of somites on the 2nd day — 20–22 pairs
• Closure of the allantois — 10–11th day
• Transfer to hatching trays — 20th day

By the fourth day, the blood vessels of the yolk circle become clearly visible during candling. At this moment, the vitelline membrane dissolves, and the yolk separates into a thick lower layer and a liquid upper layer. The albumen loses moisture and condenses under the forming yolk sac. On the fifth day, the head region grows actively, the pigment layer of the eye retina forms, and the liver begins to produce blood. The primary kidney enlarges and begins to excrete waste products.

On the sixth and seventh days, the embryo begins to make its first movements thanks to muscle development. The lungs, esophagus, stomach, and eyelids begin to form. The volume of the yolk stabilizes, as the process of consuming liquid yolk begins to exceed the rate of its replenishment from the albumen. All kidney waste products accumulate in the cavity of the allantois.

The second half of incubation: change in nutrition type and preparation for hatching

On the tenth day of incubation, the type of nutrition and respiration of the embryo changes fundamentally. By the end of the tenth or beginning of the eleventh day, the vascular network of the allantois fully closes at the sharp end of the egg. The embryo begins to ingest and digest the amniotic fluid in the gastrointestinal tract. Upon examination of a normal embryo, the primordia of the comb, feathers on the wings, a pigmented eye, and formed limbs are visible.

By the 14th day, the albumen continuously enters the amnion cavity, which leads to its severe stretching. The embryo actively uses the albumen enterally—the glandular stomach and pancreas begin to function. The embryo's body is already fully covered with down, and it performs complex movements.

The beginning of the 20th day is a critical stage for transferring eggs to the hatching trays. During this period, the circulatory system of the allantois ceases to function, and the chick begins to breathe with its lungs. At the same time, the retraction of the yolk sac into the abdominal cavity is completed. Because the chick arches its neck before pipping, the boundary of the air cell becomes jagged, and the shadow of the beak is visible inside.

1. Day 1: Evaluate the quality of embryo development. Strong offspring hatch only from eggs with an embryo that is well-developed at the first stage.
2. Day 4: Perform candling to monitor the development of the blood vessels of the yolk circle.
3. Day 10: Lower the humidity in the incubator to remove excess water from the allantois and protect against overheating.
4. Day 20: Transfer the eggs to the hatching trays, increase humidity, and strengthen ventilation for a safe transition to pulmonary respiration.

Physiology and stages of chick hatching

A normally developed embryo hatches on the 21st day of incubation. By this moment, the yolk is fully retracted into the abdominal cavity, and the umbilical ring narrows and scars over. The process of breaking free from the shell is triggered by the transition to pulmonary respiration. The chick's body presses the allantoic vessels against the shell, which hinders blood flow and reduces oxygen intake. An excess of carbon dioxide in the blood stimulates the nervous system and triggers respiratory and muscular movements.

1. The yolk is fully retracted into the abdominal cavity, the umbilical opening closes.
2. The chick presses the allantoic vessels against the shell, restricting oxygen inflow and switching to pulmonary respiration.
3. The accumulation of carbon dioxide in the blood activates respiratory and muscular reflexes via the nervous system.
4. The embryo pushes its legs against the shell and rotates counter-clockwise around the longitudinal axis of the egg.
5. The beak breaks the shell, the shell cracks, allowing the chick to emerge.

• Hatching time — 21st day
• Direction of rotation during pipping — counter-clockwise
• Main stimulus for muscular movements — concentration of carbon dioxide

Nutrient dynamics and water metabolism

The development of the embryo depends directly on the dynamics of water and egg nutrient consumption. Water provides the egg with high thermal capacity, maintaining a stable and uniform temperature inside it. It also dissolves nutrients, participates in tissue formation, and removes toxic metabolic products. Monitoring moisture evaporation in the incubator is critical at all stages of development.

Carbohydrates ensure high solubility, permeability, and digestibility of nutrients. Their relative content in the embryo tissues is at its maximum on day 5, while the glucose level in the albumen and yolk drops during the first half of incubation. The total amount of carbohydrates in the egg decreases by day 8 but increases again by days 10–11 due to fat conversion. Sugar accumulates in the embryo's body until day 11, after which its level decreases, with glycogen being detected first in the heart and then in the liver.

Protein metabolism is restructured as the embryo's mass grows. At the beginning of incubation, protein is assimilated poorly, and ammonia is the main product of nitrogen metabolism. Over time, the utilization of protein nitrogen becomes more complete: urea becomes the end product of metabolism, and uric acid in the later stages.

Fats serve as the main source of energy; their consumption is most intensive during the final days of incubation. At the beginning of development, the embryo consumes mainly unsaturated fatty acids. Closer to hatching, the utilization of unsaturated and saturated fatty acids becomes equal.

Regulation of gas exchange and heat balance of eggs

The oxygen demand and heat production of the developing embryo change constantly throughout incubation. In the first days, oxygen reaches the embryo directly from the yolk due to the activity of the enzyme catalase. From days 6–7, the circulatory system of the allantois begins to perform the respiratory function, and in the final days of incubation, its gradual atrophy occurs, and the embryo switches to pulmonary respiration.

The main gas exchange occurs through the air cell of the egg, the permeability of the shell over which increases by the end of incubation. The growing embryo absorbs oxygen faster than it penetrates from the outside, so the composition of gases in the air cell undergoes significant changes. In this process, the total amount of consumed oxygen and released carbon dioxide during the development period is strictly defined.

• Oxygen demand per 1 egg — 4777.5 cm³
• Carbon dioxide release per 1 egg — 3356.9 cm³
• O₂ content in the air cell — decreases from 20% to 12%
• CO₂ content in the air cell — grows from 1% to 6%

The temperature inside the egg directly depends on the heat production from the oxidation of nutrients. During the first half of incubation, the egg temperature is equal to the air temperature in the incubator or stays below it. After day 10, the egg temperature no longer drops below the chamber temperature and continuously rises until the moment of hatching.

Chronology of the formation of internal organs and embryonic membranes

For proper control of the incubation process, a technologist needs to be oriented in the stages of formation of the embryo's life support systems. In the first days, the neural tube is transformed into the spinal cord, and immature cells (neuroblasts) migrate from it to form ganglia and peripheral nerves. On the head, the hemispheres, diencephalon, midbrain, hindbrain, and cerebellum are sequentially laid down from the brain vesicles. Near the diencephalon, the gonads and endocrine glands — the pineal gland and pituitary gland — develop.

The embryo's heart in the early stages consists of one atrium and one ventricle and lies outside the body. Later it is transformed into a four-chambered one, but the atria remain connected by an opening until pipping, and blood from the lungs is directed straight into the aorta, as circulation is not yet divided into systemic and pulmonary circuits. Vessels, initially consisting only of endothelium, are gradually covered with mesenchyme, forming muscle elements and the outer shell.

The primary gut, initially closed at both ends and straight, eventually develops into the esophagus, stomach, and intestines. The formation of respiratory organs, digestive glands, and auxiliary membranes follows a strict schedule:

1. Day 3: the trachea and lungs, as well as the thyroid, parathyroid, and thymus glands, are laid down in the pharynx from the ventral side in the form of an outgrowth.
2. Day 4: the folds of the amnion, forming from the ectoderm and the outer layer of the mesoderm, fuse over the embryo; during this same period (on days 4–5), the liver and pancreas are laid down.
3. Day 5: the three-layered blastoderm spreads over the yolk and covers half of its area.
4. Day 10: blood vessels almost completely cover the yolk, forming the yolk sac (developing from the entoderm and the adjacent layer of mesoderm), which is connected to the midgut by the yolk stalk with arteries and veins running through it.

The yolk sac serves as a temporary organ for nutrition and respiration. Substances are absorbed in its walls, passing into the blood, and hemoglobin is oxidized. The sac grows with villous folds deep into the yolk to increase the absorption area, and at the end of incubation, along with the residual yolk, it is drawn into the abdominal cavity of the embryo, where it is then completely resorbed.