Reproduction, organ structure and development of birds (biology, grade 7)

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The middle zone is characterized by spring breeding and development of birds. In the spring, insects appear, it becomes warm, and building material for the nest is found. Ideal conditions are created for raising offspring.

Reproductive system

Birds are oviparous dioecious animals. Sexual dimorphism is most often pronounced. Males are more attractive than females.

The reproductive system of females is represented by the left ovary (the right one is reduced) and the oviduct. The absence of the right ovary is due to two reasons:

• one ovary significantly lightens the weight of the bird, which is important for flight;
• Only one large egg can pass through the narrow oviduct.

By the beginning of reproduction, the ovary swells with numerous follicles and takes on the appearance of a bunch of grapes. The oviduct - a long tube with internal glands - extends like a funnel from the ovary, passes into the extension (uterus) and opens outward into the cloaca, through which fertilization and release of the egg occurs.

Follicle is a structural part of the ovary, consisting of an oocyte and an epithelial layer. After maturation, the oocyte produces an egg, which passes from the ovary into the oviduct.

Males are characterized by the presence of paired testes, from which vas deferens extend, ending in a cloaca. Most birds do not have an external male genitalia. The exception is ducks, which have a spiral-shaped penis. Also, some species of birds (ostriches, geese, craxes) have a copulatory organ that extends from the wall of the cloaca.

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Biology (8th grade): Birds

The structure of the internal organs of birds

Rice. 1. The structure of the reproductive system of birds.

Mating Features

Most bird species have similar reproductive patterns. But still, each representative has its own individual characteristics.

The mating process can be examined in more detail using the example of chickens. Although it should be noted that females of this species can lay eggs without males . In this case, the egg comes out unfertilized.

At a certain period, the testes of males begin to rapidly increase in size. At this time they are ready to mate. A few days later the female lays eggs. Their number differs among individual species.

The mating period for different individuals can occur at different times. Some species will be ready to breed in the spring or summer, while others will wait until early autumn before laying eggs that will produce chicks.

Egg structure

The egg itself (ovum) - the yolk - is fertilized in the upper part of the oviduct and, passing from the ovary through the uterus to the cloaca, is covered with protein, films, and a calcareous shell. It takes 12-48 hours for the formation of an egg in the oviduct in different species of birds. The internal structure of the egg is described in detail below.

• Yolk . Consists of nutrients and water necessary for the development of the embryo. In the upper part of the yolk there is always a germinal disc or blastodisc - a small accumulation of cytoplasm with a nucleus. The blastodisc is isolated and stands out on the yolk as a light spot. An embryo develops from it. The yolk is covered by a membrane that separates it from the white.
• Protein . Protects and provides the embryo with water. The protein is surrounded on top by two dense shells, which separate at the blunt end, forming an air chamber. As the embryo grows, the chamber enlarges and the chick begins to breathe with a supply of air.
• Chalazy . Protein cords (clumps of protein) extending from the inner shell and holding the yolk suspended in the middle of the egg. The cords protect the embryo from shock and damage.
• Shell . The upper hard shell is permeated with numerous pores through which gas exchange occurs. The shell can be painted with a special pigment for camouflage in open nesting conditions. A thin shell covers the top of the shell.

Rice. 2. Internal structure of the egg.

Physiology of bird reproduction

Male reproductive organs

. They consist of testes, tubules, vas deferens, appendages, seminal ampoules (vesicles) and copulatory organs. Males of all bird species have two testes, which are located symmetrically on either side of the midline near the anterior end of the kidneys, near the adrenal glands. Their shape is oval or bean-shaped (Fig. 7). The color is whitish or yellowish. The testes are the sex glands in which sperm develop and mature. Each testis has an appendage, which is enclosed with it in a common capsule.

Mature testes have stratified epithelium, representing the various stages of spermatogenesis. In addition, on the walls of the testes and in the lumens of the tubules there are feeding cells (Sertoli cells), to which spermatids and sperm are attached. The connective tissue of the intertubular side contains interstitial cells (Leydig) and blood vessels. The weight and size of the testes depend on the species, age, breed and physiological state of the bird. During the period of sexual activity, the testes, especially in drakes and geese, increase many times. The weight of the testes in roosters of egg lines reaches 45 g, in meat lines - 70 g, in drakes during sexual activity - 50-70 g, in ganders and turkeys - 30-50 g. Mature testes have large convoluted tubules with stratified epithelium. From the wall of the tubule to the lumen there are spermatogonia, first-order spermatocytes, second-order spermatids and sperm in

(spermatozoa).
Males of light breeds reach sexual maturity much earlier than males of heavy breeds. Mature sperm, depending on individual characteristics and conditions of keeping and feeding, appear in roosters of egg lines at 9.5-24 weeks of age, in turkeys - at 21-30, in drakes - at 20-25, in ganders - at 25-35 -weekly. The testicular appendages
are poorly developed.
They are oblong in shape, yellowish in color and are clearly visible only during sexual activity. The appendage consists of a main, central canal and many lateral branches. Unlike male mammals, in which the “ripening” of sperm occurs in the epididymis, in birds, the majority of sperm produced in the testes through bundles of tubules, bypassing the epididymis, enters directly into the vas deferens. The vas deferens
are thin convoluted tubes.
The appendages and vas deferens change depending on the condition of the testes. If the activity of the testes increases, then the walls of the vas deferens become thicker, the lumen becomes wider, and the number of twists increases. The vas deferens open into the cloaca, before entering which small expanded thickenings (seminal vesicles) are formed, usually filled with sperm. The holes through which the vas deferens opens into the cloaca have small thickenings called genital papillae. Male geese and ducks have a sexual organ for copulation.
It has the shape of a spirally twisted, worm-shaped body, the length of which reaches 7-15 cm. The outer part of the genital organ has pointed horny elevations, which are especially pronounced near the philtrum.
A cord consisting of elastic fibers runs along the longitudinal axis of the genital organ. Erection in male birds, unlike male mammals, occurs exclusively under the influence of lymph entering the penis. Turkeys and roosters have a small rudiment for copulation - a copulatory organ
(follus), which, at the time of erection, protrudes from the male's cloaca in the form of a small onion-shaped protrusion.
In male guinea fowl, the copulatory organ is elongated - 3-5 cm. Sperm flows through the gutter. The process of development of male germ cells - spermatogenesis
in birds occurs in the same way as in other vertebrates. Spermatogenesis begins with the formation of primary germinal germ cells - spermatogonia, characterized by a round shape and the presence of relatively large nuclei. There are four stages of spermatogenesis, during which the primary germ cells - spermatogonia - transform into mature sperm. Bird sperm differs from mammalian gametes in having a smaller volume (9.2 µm3) and less intense metabolism. The latter is probably due to the significantly lower motility of avian sperm compared to mammalian sperm. The speed of movement of rooster sperm is 61 mm/h, rams - 276 mm/h, bulls - 540. The head of rooster sperm is very long (12.5 µm), cylindrical and consists of a chromatin substance, covered at the top with a conical acrosome (2 µm), which easily separates from the head under the influence of distilled water. There is no spiral filament in the sperm body, and mitochondrial ranulae are located in pairs symmetrically on the sides of the axial filament. The tail spiral sheath is also absent, the axial filament is covered only with an amorphous membrane. The length of the middle section is small (4 µm) compared to the main part (80-90 µm) of the tail. The total number of mitochondria in a rooster is about 30, and in a bull, for example, 80-85. It has been proven that liquid secretions (lymphatic fluid) are not an ideal medium for storing sperm. The presence of large amounts of lymph fluid reduces the quality of sperm during storage. Bird sperm, like mammalian sperm, is characterized by a predominance of catabolic processes over anabolic ones. The inability to assimilate, synthesize, and accumulate organic substances are essential properties of sperm metabolism. Therefore, the most likely reason for the death or decrease in the fertilizing ability of sperm in the external environment when storing whole, undiluted sperm is the consumption of one’s own energy resources. Bird sperm are characterized by both aerobic oxidation and glycolysis. Energy metabolism occurs in the same way as in mammals. There are few reducing sugars in bird sperm - on average 31.7 (7.7-81) mg%. The main energy material that ensures sperm motility is glucose, the intensity of which depends on the temperature of sperm storage. So, if at a temperature of 0-2°C glucose is used by 40% per day of storage, and up to 80% in two days, then at a temperature of 22-24°C these figures are 80 and 100%, respectively. When the temperature rises to 38-40°C, glucose is completely used within 1 hour of storage. Spermine move thanks to the presence of a contractile protein in their tail - spermozine.

Female reproductive organs.

They consist of one left ovary and oviduct.
The ovary
is an organ where egg cells (yolks) are formed, enriched with nutrients.
In a bird embryo, two ovaries are formed, but then, during development, the right one soon atrophies, and the left one reaches its full development. On the outside, the ovary is covered with a two-layer (epithelial and connective tissue) membrane, under which germinal follicular cells are located. In appearance, the ovary resembles a bunch of grapes. Each egg is loosely attached to the ovary by a process or stalk connected to the vascular and connective tissue of the ovary. With a process it attaches to the dorsal surface of the abdominal cavity and large blood vessels. During prolonged oviposition, the ovaries reach their maximum weight and size, and during a pause they decrease significantly. So, in a chicken, the weight of the ovary in a resting state is 2-4 g, and in the active state it is 45-56. During the molting period, the weight of the ovary decreases to 6-8 g. The oviduct
is the organ where the bird’s egg is formed. Sperm live and are stored in the oviduct from insemination to fertilization. The oviduct is a long, winding tube-like organ (Fig. 8). It is located on the left side of the abdominal cavity. The walls of the oviduct are elastic and very variable in size. The upper part of the oviduct (funnel) opens into the body cavity near the ovary, but is not connected to it. The lower part of the oviduct opens into the cloaca. The length of the oviduct in non-laying hens is 11-18 cm, and the diameter is 0.4-7. During maximum egg production, the size of the oviduct increases, reaching 37-86 cm in length and 6-10 in width. It consists of 5 parts: the funnel, the albumen, the isthmus, the uterus and the vagina.

The funnel has an oval hole with a diameter of 8-9 cm, opening into the abdominal cavity. The walls of the funnel are connected to the abdominal wall by muscular ligaments. These ligaments are very elastic and provide good mobility of the funnel. Thanks to this mobility, the funnel captures mature - the largest follicles from the ovary after ovulation. In the funnel, fertilization of the egg occurs with sperm. The egg remains in this area for 15-20 minutes. The funnel ends with a strongly narrowed tube (neck of the funnel), which passes into the protein part of the oviduct. The albumen part is the longest section of the oviduct (30-36.5 cm). In this department, which is constantly functioning, the egg white is secreted as the yolk (egg) passes through it. The mucous membrane of the section is collected in 15-25 main longitudinal folds 4-5 mm high and 2.5 mm thick. In the protein chamber, the formed egg is enveloped in protein within 3-3.5 hours. The isthmus follows the protein portion of the oviduct. The isthmus is a relatively short section of the oviduct (8-10 cm). It has a relatively thick layer of circular muscles. Here the shell membranes of the egg are formed. The isthmus without clear boundaries passes into the uterus. The uterus is the widest part of the oviduct, having a short length (8-10 cm). The uterus has a thick layer of longitudinal and circular muscles. Its mucous membrane gathers into folds, so that it can expand during the passage of the egg. At the lower end of the uterus there is a strong muscular sphincter ring. The egg shell is formed in the uterus. The cervical canal not only takes part in the formation of the egg, but is also a place for the accumulation and storage of sperm. The vagina is the final section of the oviduct. Its length is 3.5-5 cm in chickens and turkeys and 4-8 cm in geese and ducks. It has a well-developed layer of circular muscles. The inside of the vagina is lined with a mucous membrane that forms low, narrow, ridged folds.

Regulation and factors stimulating egg laying

The process of development and functioning of the gonads is under constant neurohumoral influence. Morphologically and functionally, the reproductive organs of birds are connected to the central nervous system; they are innervated by sympathetic and parasympathetic nerves.

In this process, a large role is given to humoral factors; the pituitary gland, ovary, thyroid and other endocrine glands take part in it. The place of formation of gonadotropic hormones in birds, as well as in mammals, is the pituitary gland. Removal of the glandular lobe of the pituitary gland leads to a delay in the development of the gonads. The pituitary gonadotropic hormone begins to be produced in sufficient quantities only from a certain age, close to puberty.

The pituitary gland secretes follicle-stimulating hormone, which promotes the development and maturation of eggs, luteinizing hormone, which affects ovulation, the release of the egg from the membrane, etc. The release of these fibers is regulated by the nervous system. While the protein is in the protein part of the oviduct, even for a long time, the next ovulation does not occur.

As the egg passes through the isthmus of the oviduct, nerve impulses enter the central nervous system, hypothalamus and pituitary gland, after which another ovulation occurs.

The ovary produces steroid hormones that regulate the function of the oviduct, which is most sensitive to estrogens and increases in size when they are administered. Ovarian hormones also influence the function of the mucosal epithelium and the development of the oviduct apparatus. Adrenogens and other hormones also play a large role in these processes.

The most important condition for increasing the egg production of birds is their rational feeding. The intensity of the processes occurring in the body of birds during the egg-laying period can be judged by the level of excretion of various organic and inorganic compounds with eggs.

Chemical composition of chicken eggs (%): water - 65.5; protein -11.9; lipids - 9.3; carbohydrates - 0.9; minerals - protein and yolk - 0.9 g; shell - 11.5.

Together with the shell, 600 g of calcium, or one third of its live weight, is excreted from the chicken’s body per year. Over the course of a year, a chicken produces 8 times more egg mass with high-value nutrients than it weighs itself, including an amount of protein equal to its live weight. If we compare the protein production of a chicken with a cow (milk yield 4000 kg, protein in milk 3.3%, live weight 600 kg), then a chicken produces 0.9 parts of protein per unit of body weight per year, and a cow only 0.23. The egg white contains all the essential amino acids, various macro- and microelements.

Nutrients must constantly be supplied to the bird's body with food and in such a form that the bird spends as little energy as possible on their absorption. During certain breeding periods, metabolism changes dramatically.

For example, gas exchange in males during sexual activity increases significantly, and in general it is 20–30% higher in them than in females. Before the laying season, the liver of chickens increases in size and its protein-forming function increases. At this time, the calcium content in the blood increases approximately 2–3 times.

Emergence and development of chicks

Speaking briefly about the reproduction and development of birds, four behavioral features should be highlighted:

• pair formation;
• pairing;
• nesting;
• caring for offspring.

Males attract females for mating by organizing mating games. Birds singing, male fights, nest building, decorations and gifts are attributes of courtship or mating with a female. Depending on the species, males may seek a mate for life or seasonally.

After mating, the birds nest. They build their nests independently from clay, branches, pebbles, or occupy other people’s houses. Birds lay 1-20 eggs.

For the development of the embryo, high temperature (38-39°C) is required. Therefore, birds incubate the eggs, periodically turning them over. The formation of the embryo ends on days 16-40, depending on the species.

Rice. 3. Development of the bird embryo in the egg.

After the birth of the offspring, the birds show care for some time in pairs or individually. Based on the duration of development, chicks are divided into two groups. The characteristics of the groups are described in the table.

The importance of birds in nature

Birds play an important role in biogeocenosis. They take part in many biological circuits. Herbivorous species eat fruits, seeds and shoots of plants. Some representatives store food, carrying it for many kilometers. Along the way, some of the seeds may be lost. This helps plants spread over large areas.

Insectivorous species are also important . With their help, insect populations are controlled. Without these birds, a person would not be able to get a good harvest from the sown fields.

People are trying to help birds survive difficult winters. They set up temporary nesting sites everywhere, where blue tits, flycatchers, and tits move in. During the cold period, birds feel a lack of food, so they need to be fed with bread crumbs, seeds or small fruits.

Some species are commercial. For example, these are black grouse, ducks, hazel grouse, and geese. They are considered quite valuable to humans. There are also birds that are used for sporting purposes. These are waders, snipe and woodcock.

Thus, birds, despite many differences in appearance, lifestyle, etc., have a large number of similar features and are very important in nature.

Two roosters in one yard: leveling out conflicts

If the poultry yard is organized for the purpose of obtaining chicks, it is impossible to do without males. However, they have difficulty getting along with their competitors: other contenders for the female often show aggression.

Methods for resolving conflicts between male roosters, geese, and turkeys:

• choose males from one brood,
• give preference to balanced individuals,
• let one of the two be younger, since he will show less attention to females,
• transplant the young animals to the old rooster, and not vice versa, since strong individuals in their territory will kill the old weakened rooster and continue to fight among themselves for the new territory.

It is extremely important to avoid civil strife, since all male activity should be aimed at creating offspring.

Fallowing guinea fowl and quails in artificial conditions

Other types of birds are also bred on farms. These are guinea fowl, ostriches, swans, pheasants and quails. The priority for humans is to create favorable conditions for pets for comfortable reproduction.

Guinea fowl require large territories. Otherwise, they are unpretentious and very productive, and their eggs are larger than chicken eggs. In addition, they easily get along with other inhabitants of the poultry yard: chickens, turkeys, geese.

Keeping quails has become a profitable business, since their eggs are twice as expensive as chicken eggs, and the meat is considered dietary. The payback on breeding occurs quickly, the costs of the project are relatively low.

Breeding ostriches, swans and pheasants

Ostriches are polygamous, so one sire is enough for a harem. During the mating season, it becomes aggressive, and its legs and neck become reddish in color. During the day, the eggs are incubated by the partner; at night, the partner takes over this responsibility.

Swans mate for life. They build nests up to three meters in diameter, where they incubate 3-5 eggs for up to 40 days. The chicks are born already covered in fluff. Parents take care of their children for up to a year.

Males are aggressive and behave like roosters. Therefore, the same requirements apply to them. There are no more than three partners per manufacturer.

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How to find out if a male is ready to breed

Many people are wondering how to know that the mating season has begun and the male is ready to breed? In fact, the correct answer to this question is very simple.

The fact is that the male himself makes it clear that the time has come. This can be understood by the sudden increase in the tendency to court females. The feathered suitor will be ready to devote absolutely all his strength to avoiding the female. Namely: he will defiantly spread his tail, clean his feathers and go on the attack.

A funny example can be given: at such moments, parrots begin to playfully knock with their beaks and also jump around their chosen one. They bring her food, as well as other gifts. As you can see, they try to gain the female’s favor by any means.

There are a huge number of original birds that use very unusual ways to please their chosen one and beat all rivals. Thus , peacocks are able to reveal their huge, beautiful tail. Pigeons puff up and stick out their chests to make them appear larger than they really are. The dolphins start dancing. But the funniest option was offered by Argentine ducks. They simply show the female their genitals, and she herself chooses from the presented variations.