Morphofunctional features of the mammary gland in different animal species. Structure and function of the mammary gland in animals

Breast development.

The mammary glands are derivatives of the skin. Each gland is a collection of glandular parenchyma with a corresponding number of nipples. A cow has four glands (two on each side), sheep and goats have two (one on each side), and a horse has four glands (but only two teats).

A cow's four mammary glands form one organ called the udder. The udder is divided into two halves, each consisting of two quarters. Each quarter of the udder is a separate, independent formation. The parenchyma is divided into lobules. A lobule is a part of the secretory apparatus of the udder, separated by layers of connective tissue in which blood vessels and nerves pass. The lobule consists of many microscopic spherical formations - alveoli with a diameter of 0.1 - 0.5 mm. Their wall is based on elastic fibers, consists of one layer of secretory epithelium and is abundantly supplied with capillaries. The wall also contains stellate myoepithelial cells that perform a contractile function. A thin alveolar milk duct emerges from the alveoli, through which milk flows into a larger excretory duct formed by a group of alveoli. The excretory ducts merge to form intralobular ducts, or milk canals. The latter flow into large milk passages that open into the tank (Fig. 1).

Mammary gland tissue undergoes cyclic changes associated with the sexual function of the animal. Intensive growth of glandular tissue occurs after puberty of the animal and especially after the onset of the first pregnancy (from its middle to the end). Milk formation - lactation begins after calving (it lasts on average 305 days in cows, 60 days a year in pigs). At the same time, the development of the secretory apparatus of the gland continues, which causes an increase in milk production in the first months of lactation. After this, milk production gradually decreases.

Rice. 1. Diagram of the structure of a cow’s udder:

1 – skin; 2 – superficial fascia; 3 – deep fascia; 4 – milk alveoli with alveolar ducts; 5 – excretory tubules; 6 – milk ducts; 7 – milk passages; 8 – milk tank; 9 – nipple canal; 10 – sphincter canal; 11 – smooth muscles of the nipple; 12 – smooth muscles of the mammary ducts; 13 – nerves; 14 – artery; 15 – vein; 16 – connective tissue

Towards the end of lactation, several weeks before calving, when intensive growth of the fetus occurs, involution of the mammary gland occurs: the alveolar tissue is reduced, replaced by adipose tissue, the size of the gland decreases, and it ceases to function. The “dry” period begins.

Involution of the udder lasts 12–15 days, after which the restoration of the glandular tissue of the udder begins, and the animal’s body prepares for the next lactation.

Physiology of the mammary gland.

The alveolar cells of the mammary gland secrete the components of milk and release it into the lumen of the alveoli. The substances necessary for this are brought to the gland by blood.

Water, vitamins and some mineral ions pass into the cavity of the alveoli through simple filtration. Glucose, amino acids, calcium, and phosphorus are selectively absorbed from the blood. Milk sugar, casein, and milk fat are synthesized by the epithelium of the alveoli. This synthesis occurs from “precursors” supplied with the blood.

In the alveoli and ducts of the mammary gland, reverse absorption (reabsorption) of ions of certain mineral substances also occurs. A large number of enzymes belonging to the synthesis group were found in the glandular tissue of the udder.

The activity of the mammary gland is under constant control of the endocrine system, especially the hormones of the anterior pituitary gland and ovary. Metabolic and synthetic processes in the mammary gland are also influenced by hormones of the thyroid gland, adrenal cortex and pancreas.

The mammary gland secretes milk continuously. In the intervals between milkings, it fills the capacitive system of the udder: the cavity of the alveoli, excretory ducts, milk canals, milk ducts and the cistern. As the system fills, the pressure increases and, reaching a certain value (40 - 50 mm Hg), becomes a factor inhibiting milk formation.

The removal of milk is a complex reflex involving neuro-hormonal mechanisms. Irritation of numerous nipple receptors during milking causes a flow of impulses into the central nervous system, reaching the hypothalamus. The hypothalamus stimulates the posterior lobe of the pituitary gland to secrete oxytocin (residual milk can be extracted by injecting the animal with large doses of the hormone oxytocin), which, entering the blood, is carried to the mammary gland and causes contraction of the myoepithelium of the alveoli and small ducts. The milk is squeezed out (“discharged”) into large ducts and a tank.

BREAST PATHOLOGY
The mammary gland, like the genitals, must be considered as an organ that, under natural conditions, functions only during the suckling period; it evolves in connection with childbirth and involutions when the offspring can already exist without mother’s milk. Under natural conditions, this is followed by a new pregnancy, and in production, lactation is combined with pregnancy based on economic feasibility. The mammary gland is an organ that produces an essential food product (colostrum) for the newborn and milk. Therefore, after a brief description of the anatomy and physiology of the mammary gland, we outline the main provisions of the doctrine of the forms of agalactia (lack of milk) and hypogalactia (low milk supply).

BRIEF MORPHOFUNCTIONAL CHARACTERISTICS OF THE UDDER

The mammary gland, udder, is a glandular organ consisting of four quarters; each of them ends at the bottom with a nipple. Some cows have two, less often four, additional quarters, usually poorly developed, without glandular tissue and a teat canal. The skin of the udder is covered with delicate sparse hair; on the back surface of the udder they grow from bottom to top and to the sides, forming the so-called milk mirror. The shape and size of the milk mirror varies. The udder fits tightly to the ventral abdominal wall and is held in position by the suspensory ligament of the udder and fascia.
Components of the udder: glandular tissue, excretory ducts, interstitial connective tissue, blood vessels, lymphatic vessels and nerves. The right and left halves of the mammary gland are separated from one another by the suspensory ligament of the udder, which serves as a continuation of the yellow abdominal fascia. Under the skin is the superficial fascia of the mammary gland, covering each half of the udder. The superficial fascia is followed by its own fascia, covering the glandular part of the udder and giving branches (trabeculae) into the parenchyma, dividing it into quarters and individual small lobules; each lobule is surrounded by an interlobular connective tissue membrane.
The parenchyma of the udder consists of glandular alveoli and excretory ducts, forming an independent, separate system in each quarter of the udder. The alveoli are lined with secretory cells that produce milk. Each alveolus and the duct extending from it are externally entwined with stellate cells (myoepithelium) and their processes. When stellate cells contract, they squeeze the contents of the alveoli into the ducts. Small ducts depart from the alveoli, which unite to form the middle ducts. The areas of parenchyma with these ducts form independent lobules of the udder, surrounded by a more or less pronounced layer of interlobular connective tissue.
The middle ducts, heading down towards the nipple, merge and give rise to 12-50 wide excretory ducts - milk passages flowing into the cistern. Milk tank - the cavity of the nipple, sometimes extending upward into the parenchyma of the udder, serves as a reservoir for milk.
The nipples are conical, bluntly ending branches of the mammary gland. The nipple has a base that passes without sharp boundaries into the body of the udder lobe, an apex that freely hangs down, and a cylindrical part located between the apex and the base of the nipple. The length of the nipples, depending on the age, breed and milk production of the cow, varies from 4 to 10 cm. The wall of the nipple is made of skin, connective tissue and mucous membranes. The skin does not contain hair, sebaceous and sweat glands; at the apex it passes into the mucous membrane of the nipple canal, which connects the cavity of the cistern with the external environment. The connective tissue layer of the nipple wall has bundles of smooth muscle fibers that form plexuses running in different directions. At the apex of the nipple, the muscle fibers are collected into a clearly defined circular layer - the sphincter of the nipple canal. Its length is 5-10 mm, diameter 2.5-3 mm. The lumen of the nipple canal is closed by a contracted sphincter and small longitudinal folds of the canal shell tightly adjacent to each other, forming a rosette on the side of the cistern, which is important for tightness. 0.8 - 1 liter of blood, and during lactation - 4 liters or more.
Arterial system of the cow's udder. You should pay attention to the following features of the blood supply to the udder: perineal arteries branch on its posterior surface; there are anastomoses between the arteries of the right and left halves of the udder; The perineal vein carries blood from the genitals to the udder. The latter fact is of great importance for explaining cases of udder disease with damage to the genital organs, as well as the endocrine influence of sex hormones on the udder.
The udder is very rich in blood vessels; arterial and venous capillaries form a dense network around each alveoli. The intensity of blood supply to the udder depends on its functional state.
The venous system of the udder is more developed than the arterial system. There are a large number of additional venous vessels, often anastomosing with each other and with the veins of the adjacent quarter. There are also anastomoses between the veins of the right and left halves of the udder.
Venous blood flows from the udder through three paired vessels:
1) along the external pudendal vein, running together with the external pudendal artery;
2) along the subcutaneous abdominal mammary vein, which, moving forward, is clearly visible under the skin with its convolutions and penetrates through the mammary well into the abdominal cavity, where it flows into the internal ore vein;
3) along the internal pudendal vein.
Venous trunks, mainly superficial, form a large number of convolutions and ampulla-shaped extensions, mainly at the base of the nipple, which gives the udder tuberosity. The circular venous plexus, located at the border of the cistern and parenchyma, can close the lumen of the cistern when overfilled with blood.
The lymphatic system of the udder originates from the lymphatic slits and spaces located around the alveoli. From here, the lymph collects in the interlobular lymphatic vessels, passes through the lymph nodes into the lymphatic cistern, and from there along the thoracic duct into the vena cava. The rich network of lymphatic vessels of the skin of the udder begins in small stems at the base of the nipple. They form a large number of anastomoses between themselves and the deep lymphatic vessels of the corresponding quarter, uniting in each lobe into independent trunks, separately flowing into the suprauterine lymph nodes the size of a hazelnut or a pigeon egg. The suprauterine lymph nodes are located at the base of the posterior lobes of the udder. From each node, lymph is carried out by two large lymphatic vessels or bundles of vessels. One of the efferent vessels goes to the perineum and unites here with the lymphatic system of the rectum and external genitalia; the other vessel goes to the groin area, to the inguinal lymph nodes. In addition to the main lymphatic vessels, there are a number of small ones that densely penetrate the parenchyma of the gland.
The degree of lymph circulation in the mammary gland in lactating animals is directly dependent on the level of milk production. In dry cows it is approximately 6 times less than in milk cows (I.K. Medvedev).
The innervation of the udder is carried out by branches and, finally, branches from the dense nerve plexuses surrounding the vessels of the udder. The nerve fibers of the parenchyma form dense plexuses around the alveoli and lobules of the gland. Clearly distinguishable nerve trunks go, accompanying the vessels of the cistern and milk ducts, to the milk cistern and nipple, where they end in the skin of the nipple and in the mucous membrane of the cistern. Irritation of receptors located deep in the udder tissue affects the animal’s blood circulation, breathing, digestion and reproductive system.
The pituitary gland reacts by increasing or decreasing the release of hormones under the influence of visual, auditory and olfactory perceptions.
The mammary gland of sheep and goats consists of two
halves, clearly demarcated by the inter-udder furrow. In structure and function, the mammary gland of these animals does not differ significantly from that of a cow. It should be noted only the conical shape of the nipples and the strong sagging gland in the goat, which causes frequent mechanical damage to the udder. The innervation of the udder is carried out by branches of the lumbolateral nerves, arising from the first and second lumbar nerves, passing along the abdominal wall of the corresponding side and branching in the skin and parenchyma of the udder. In sheep, the nipples are short, the udder lobes are rounded, the teat canals are somewhat longer (up to 1 cm) and narrower (this is important to consider during catheterization).
The camel's mammary gland has four lobes; like a cow, it is divided into right and left halves. The nipples are short (reminiscent of the nipples of a “kumys” mare). The forequarters are less developed than the hind quarters. Milk productivity depends on the breed of the animal and ranges from 15-20 liters per day. The duration of the lactation period reaches 16-18 months.
The mare's mammary gland is covered with delicate hairless skin. During the dry period, the gland decreases so much that it almost merges with the skin of the abdomen, and reduced, tightened nipples protrude on its folds in the form of laterally flattened elevations. The gland is inactive and well demarcated from the abdominal wall, to which it is suspended on a branch of the yellow abdominal fascia - the suspensory ligament, which penetrates between the halves of the udder and passes into the fascia of the mammary gland. Each half of the udder is divided into front and rear quarters, indistinguishable from the outside, having independent and separate systems of alveoli and excretory ducts, opening at the base of the nipple into two or three small cone-shaped tanks. The cisterns communicate with the external environment through independent channels, and on each nipple there are therefore two (rarely three) openings of the nipple canals, corresponding to the anterior and posterior glands. The blood supply to the gland is carried out through arteries and veins. The mammary gland of a pig consists of 8-16 (rarely 20) glandular lobes (mammary hills), symmetrically located on the sides of the white line from the pubic bones to the sternum; Sometimes the number of shares is odd. Each lobe is composed of a group of glands, the ducts of which flow into two, rarely three, small cisterns. At the top of the nipple, two, rarely three, nipple canals open. During the dry period, the lobes of the gland are pulled towards the abdominal wall and merge with it. By the time of birth, the mammary gland is secreted in the form of two powerful bars with more or less evenly developed lobes.
The dog's mammary gland consists of 10 glandular lobes located on the ventral abdominal wall. There are no milk tanks. As their lumen increases, the milk ducts unite into 6-12 large milk ducts, which open as independent ducts at the apex of the nipple; therefore, when the secretion is squeezed out of the gland, milk first appears on the surface of the nipple in the form of several small droplets, gradually merging into a common large drop. Each nipple serves its own system of alveoli and excretory ducts of the mammary gland.
During lactation, areas of the milk ducts located in the nipple can expand and take the form of small cisterns (milk sinuses).
The cat's mammary gland consists of 8 glandular lobes, located, like in a dog, on the ventral abdominal wall. The milk ducts, merging and not forming a cistern, open on the surface of the nipple with two holes.
The mammary gland of a rabbit is formed by 8 glandular lobes.
Function of the mammary gland. The mammary gland performs the function of lactation, which consists of two independent and interdependent processes: milk formation and milk output. Lactation is a manifestation of a complex non-humoral reaction of the whole organism to nerve impulses coming from receptors in the skin of the mammary gland during sucking or milking, as well as arising as a result of irritation of chemo-receptors located in the walls of the blood vessels of the gland and other organs by substances formed in the body females during certain periods of life (childbirth, pregnancy). Hormones involved in the lactation process include estrogens, progesterone, prolactin, somatotropic, thyroid-tropic, adrenocorticotropic, oxytocin, thyroxine, triiodothyronine, thyrocalcitonin, glucocorticoids, mineralocorticoids, adrenaline, norepinephrine, parathyroid hormone , insulin and glucocorticoid.
The function of the udder is closely related to the functional state of the genital organs. In a castrated immature female, the mammary gland does not develop due to the lack of estrogens. After transplanting an ovary into a castrated male, his mammary gland develops and even lactates. Subcutaneous administration of estrogens to infantile animals causes the growth of the milk ducts, and when the action of estrogens is combined with progesterone, the alveoli also grow. In the second half of pregnancy, the ovary and placenta secrete a large amount of estrogens, which cause the growth of the milk ducts and alveoli. Progesterone prepares the gland for secretion. Towards the end of pregnancy, the anterior lobe of the pituitary gland secretes the hormone prolactin, as a result of which milk is formed, i.e., secretion occurs, and the posterior lobe of the pituitary gland produces oxytocin, which causes milk secretion.
Milk formation (milk secretion) is inextricably linked with milk secretion. Without milk release (when colostrum and milk are not milked or not sucked due to the death of the offspring), as well as when milk is continuously released (for example, when a milk catheter is constantly inserted into the nipple canal or with penetrating wounds of the nipple), the formation of milk stops. An important factor in lactation is irritation of nerve endings located in the walls of blood vessels, milk ducts and in the skin of the mammary gland. Irritation of the nerve endings of the skin of the mammary gland and especially the nipple (massage, milking, sucking) is transmitted along the nerve pathways to the cerebral cortex. In response to these irritations, nerve impulses go from the center to the periphery to the mammary gland as a working organ, in some cases inducing it to secretion and milk secretion, in others inhibiting these processes. Humoral factors also play an important role in milk secretion, which, acting on the chemoreceptors of the mammary gland, cause nervous excitement. It is transmitted along nerve pathways to the cerebral cortex, and from it nerve impulses go to the mammary gland, prompting it to secrete.
All organs of the female’s body participate in the process of milk secretion and milk secretion, determining the specific, individual properties of each cow’s milk. In addition to the ovary, pituitary gland and placenta, other endocrine glands (thyroid, adrenal glands, etc.) also influence lactation. External stimuli (visual, olfactory, auditory, tactile, gustatory) also have a positive or negative effect on the function of the mammary gland. This should explain the fluctuations in the milk productivity of cows depending on the method of milking, the experience of the milkmaid, caring for the animal and diet, not only on its nutritional value, but also on its taste.
In young animals, the mammary gland consists of adipose tissue and a small number of milk ducts. With the onset of puberty, the number of milk ducts increases. A radical change in the structure and function of the mammary gland occurs in connection with pregnancy. From the second half of pregnancy, especially towards the end of it, milk ducts, alveoli and milk lobules are intensively formed.
By the time of childbirth, the mammary gland enlarges and begins to produce colostrum - a thick, viscous, yellowish-white liquid that has a peculiar, unpleasant, salty taste. Colostrum contains a significant amount of protein and salts, characteristic fat droplets (colostrum corpuscles). Colostrum contains less fat and sugar than regular milk, more iron, 10 times more retinol (vitamin A) and ascorbic acid (vitamin C), 3 times more calciferol (vitamin E). Colostrum contains large amounts
etc.................

Mammary glands are symmetrical skin formations located in pigs, rodents, and predators in the abdominal area, and in ruminants and horses - in the groin area. Each gland ends in a nipple. A cow's udder is formed from the fusion of three pairs of mammary glands. The two anterior pairs develop normally. The right and left halves of the udder are separated from each other by an elastic septum, which is also a ligament supporting the udder. The morphofunctional unit of the udder is the alveoli, located radially around the milk ducts (Fig. 67)

The alveoli collectively represent the glandular tissue of the udder. They carry out the biosynthesis of the main components of milk. The alveolus is a small bubble with a diameter of 0.1 - 0.3 mm. The alveoli are covered on the outside with a dense connective tissue membrane, under which there is a layer of contractile myoepithelium. The inner layer forms the glandular secretory epithelium.

The alveoli are intertwined with a dense network of capillaries. The mammary alveoli are combined into separate groups, each of which has a common excretory duct. These ducts gradually merge with each other and form a system of large ducts with a lumen of 5-17 mm in diameter, which end in peculiar extensions - milk tanks (Fig. 68).

Milk tanks are the container system of the mammary gland. On the surface of the cistern there are well-defined papillae and folds, richly supplied with blood and lymphatic vessels, as well as nerves. The size and shape of the nipples depends on the species and individual characteristics of the animal.

Rice. 67. Cluster of mammary gland.

Rice. 68. Transverse section through the anterior lobes of a cow's udder.

Along with the main nipples, additional ones are often found. They usually do not function, but sometimes milk can be released through them. Under the epithelium of the nipple there is a layer of longitudinal muscles, and then there is a circular layer that forms the muscular sphincter that closes the nipple canal. There are sweat sebaceous glands and hairs on the skin of the teats of a goat, sheep, mare and other animals, but they are absent on the teats of a cow. Therefore, if the udder is poorly cared for, cracks form on the teats, which makes milking the animals difficult or impossible.

A cow's udder has a significant capacity. A huge number of alveoli, milk passages, ducts and cisterns are able to accommodate a large amount of milk. The size of the capacitive system is determined by the highest milk yield in the 1-2 month of lactation.

Udder massage promotes its development. The udder capacity reaches 20 liters or more. The udder is divided by volume into large, medium and small, and by shape into bath-shaped, cup-shaped, round, goat and primitive. The best shape is considered to be a bath-shaped and cup-shaped udder with well-developed nipples. The structure of the udder is glandular, glandular-connective tissue and adipose, consisting of adipose and connective tissue. The most desirable is ferruginous; after milking it subsides greatly and becomes soft. The udder is well supplied with blood vessels, with the hind quarters of the udder being better than the front quarters.

There is a direct connection between the productivity of a cow and the development of blood vessels in the udder. The more abundantly the udder is supplied with blood, the greater the productivity of such an animal. On the side of the xiphoid process there is an opening through which the saphenous abdominal vein enters the chest cavity. This hole is called the milk well. The udder is equipped with a dense network of lymphatic vessels and has lymph nodes that act as filters and also have a protective function during inflammatory processes.

The mammary glands have sensory, motor, and secretory nerves originating from the lumbar and sacral parts of the spinal cord. There are a large number of different receptors on the skin of the mammary gland and nipples, as well as in the parenchyma. But the receptor apparatus of the mammary gland and nerve fibers can change depending on the functional state of the body: pregnancy, lactation, etc.

The growth and development of the mammary gland is closely related to the activity of the ovaries, the sexual cycle and pregnancy.

After birth, the mammary gland in animals is in a state of relative rest. In heifers up to 6 months of age, the udder is a small cavity from which a system of ducts extends. During this period, the udder increases in size mainly due to the growth of connective and adipose tissue. The glandular tissue of the udder is not developed. The most intensive development of the mammary gland begins with the onset of puberty. Moreover, the development of the udder continues with each new sexual cycle, regardless of whether the female is fertilized or not. By the fourth month of pregnancy, the glandular tissue of the udder noticeably increases, developing ducts and alveoli displace adipose tissue. The number of blood vessels and nerves increases

In the second half of pregnancy, the secretory epithelium begins to function, but this secretion cannot yet be called colostrum. It forms in the last month of pregnancy. After childbirth, the alveoli become large, their terminal stroma expands.

With a new pregnancy, additional changes occur in the structure and function of the mammary gland. The formation of glandular tissue and its increase occur again. During the period of intensive functioning, the udder reaches 3% of the animal’s weight.

The growth and development of the mammary gland continues in a cow for a number of years. With the extinction of sexual activity, senile involution of the mammary glands occurs.

Regulation of the growth and development of mammary glands (mammogenesis) is carried out by both the humoral and nervous systems. The growth and development of the mammary glands is influenced by hormones of the ovary and pituitary gland. In addition, the stimulation of mommogenesis is influenced by hormones of the placenta, adrenal glands, thyroid and pancreas.

Estrogens tend to stimulate the growth of the ducts, and progesterone, together with estrogens, is responsible for the growth of the alveoli. The introduction of these hormones leads to stronger development of the mammary gland. These hormones also have an effect on castrated animals. It has been established that the introduction of estrogen or prostaglandin helps to increase blood circulation in the mammary gland, the number of functioning capillaries increases, and at the same time the number of nerve fibers increases.

A major role in the development of the mammary glands belongs to the hormones of the adenohypophysis. The anterior lobe of the pituitary gland secretes hormones that act on the mammary gland both directly and through other endocrine glands. Complete removal of the pituitary gland leads to involution of the mammary gland. In addition to prolactin and GH, ACTH also takes part in the regulation of mammogenesis.

Mammogenesis is influenced by hormones of the adrenal cortex, but it is still difficult to judge whether they are able to have a direct effect on the mammary glands or whether their effect is associated with an influence on metabolic processes occurring in the body. Thyroid hormones also have a positive effect on breast growth. Their influence affects to a greater extent the secretory function of the gland.

The pancreas is important; its hormone, insulin, causes the growth of the mammary gland. Hormones exhibit their effect only in combination, because administering them separately significantly reduces the resulting effects than when used together. Consequently, here we can talk about the synergistic effect of hormones of the adenohypophysis and other endocrine glands.

The growth and development of the mammary glands is subject to the regulatory role of the nervous system. By influencing the receptors, and through them the central nervous system, it is possible to significantly control the development of the mammary glands of animals.

Denervation of the mammary gland in young animals that have not reached puberty significantly inhibits the growth and development of the udder. Disruption of nerve connections causes a decrease in the number of ducts in the udder. During this period, the influence of humoral links is very noticeable, but still, they cannot be of paramount importance, because it is not possible to completely restore mammogenesis in such animals.

The living conditions of animals greatly affect the development of the mammary gland, so concern for the future milk production of a cow must begin even during the formation of the embryo, during intrauterine life.

Good, proper feeding and care of animals, intense and prolonged irritation of the mammary glands during massage lead to the development of this organ and the hereditary consolidation of acquired properties.

Igor Nikolaev

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Milk is a white liquid containing small particles of fat, lactose, vitamins, and minerals. It is produced in the mammary glands of cows. The quality of milk depends on the animal’s nutrition, living conditions, age of the individual, and time of year. All the nutrients found in milk come from the blood. The anatomy of the cow's mammary gland contributes to the production of a healthy nutritious product that is necessary for both children and adults.

A cow's udder consists of 4 mammary glands. These are shares. They are interconnected, but each has a separate chamber. The lobes function independently of each other and end in the nipple. The anterior glands are smaller in volume than the hind glands, but in dairy cows all lobes are equal in volume.

The udder has a sheath of connective tissue covered with hairs. The fabric is gathered in elastic folds. They smooth out as the milk lobes fill with liquid. The udder is attached to the pelvic bones by connective tissue and ligaments. The basis of the mammary gland is glandular and adipose tissue:

• glandular tissue is formed by alveoli, cells in which milk is formed;
• Numerous blood vessels and nerves approach the alveoli. The posterior lobes are better supplied with blood, which is why there is more milk in them. Nerve fibers react to pressure, temperature changes, and chemical irritants;
• excretory channels connect the alveoli with the milk tank, the cavity in which milk accumulates. Each tank can store up to 500 ml. liquids;
• There is an exit from the tank - the nipple canal. Milk is milked through it. The nipple cavity holds 40 ml of liquid. Its inner wall is glandular, the outer wall consists of smooth fibers. The nipple has no hair. It protects the milk canal from external influences and infections. At the same time, the nipple is designed to remove milk from the gland;
• Each lobe has its own system of connecting the alveoli and milk ducts.

The function of the udder is to produce milk and release it. The bowl capacity reaches 40 kg. When the ligaments are weakened, it sinks under weight or becomes deformed. Most often, changes are due to the age of the cow and the number of calvings.

Nipples do not have sebaceous glands. During hot periods, cracks may appear on it. They cause pain to the cow when it comes into contact with grass or during milking. Nipples need care. After each milking they are lubricated with nourishing cream.

The shape of the udder varies among different breeds of cows. In dairy breeds, which are distinguished by good productive qualities, the gland has an elongated tubular shape. It is located along the abdominal cavity. Dairy-meat breeds most often have a cup-shaped udder. Its volume is large, indicating that the cow gives a lot of milk. In individuals of meat breeds, the glands are poorly developed: goat or primitive type of udder.

Speaking about the structure of the udder, it is necessary to describe the process of milk formation. The anatomy of the cow's mammary gland is such that milk production is associated with the reproductive organs. The alveoli begin to fill with fluid only under the influence of hormones, the level of which increases during pregnancy and after calving. Lactation is caused by prolactin, which is released by the anterior pituitary gland. The hormone stimulates the growth of the gland and prepares it for lactation. Lactocytes are present in the alveoli. These are the cells that produce milk from blood elements.

Fluid in the alveoli begins to be produced even before the calf is born. It is whitish in color, salty taste, viscous and thick. This is colostrum. After birth, a calf sucks out 1.5 kg of nutrient fluid in the first hours. He captures the nipple with his lips and thereby triggers the nerve impulse mechanism. The pituitary gland begins to secrete the hormone oxytocin. The hormone is captured by the receptors of the mammary gland, lactocytes begin to work and produce milk. The more often the nipple is irritated, the more milk is produced.

From the first days of lactation it is necessary to develop an udder. The cow is given a massage and all the milk is milked out, leaving the milk parts empty. After 4 hours they will fill with liquid again. It is recommended to milk cows every 6 hours. When the functioning of the mammary glands is normal, milking is carried out every 12 hours. If you exceed this period of time by 1-2 hours, the animal will have less milk. Over time, it will stop being produced.

The development of the mammary gland in cattle occurs before the 6th calving. After 9 calvings, milk production begins to decline. The cow is getting old. In dairy breeds, lactation can last until 13-16 calvings. Milk acquires its qualities and ceases to resemble colostrum 2 weeks after calving. The lactation period lasts 300 days. During this time, the animal can produce up to 16 thousand kg of milk.

The process of milking a cow

Before you start milking a cow, you need to prepare both the room and the animal. The stall is cleaned and the manure is removed. The belly, legs, hooves and udder of the cow are washed. They approach the animal in such a way that she can see the milkmaid. An enamel bucket is used as a container for milk.

The cow loves affection; you need to stroke her and talk to her in a calm voice. To keep the animal calm, it is tied to a turnstile. The tail is lightly grabbed with a whip to the leg. In order for the pituitary gland to release oxytocin into the body and milk production to begin, it is necessary to massage the cow. This is a kind of imitation of the actions of a calf when feeding, which taps the udder of the nurse with its head. Perform diagonal and horizontal stroking, circular movements with hands along massage lines. At this time, fluid from the alveoli enters the canals, the cistern and the nipple canal. As soon as the nipple has become hard and increased in size, the milking process begins.

The nipple is lightly grasped in a fist: the thumb and index finger are at the base of the nipple, at the same level. The little finger is located at the exit of the nipple canaliculus. The remaining fingers hold the body of the nipple strictly vertical. Squeeze the base of the nipple and squeeze the milk out of the tubule with your fingers.

The first drops are poured into a clean mug. The color of the milk is determined: whether there are any foreign impurities. With the first portion, bacteria and dirt come out of the teat if the cow is not washed well. The rest of the milk is milked into a container. After making the first cycle of movements with your fingers, wait until the nipple is full again. This usually takes 2-3 seconds. In a similar way, all 4 lobes of the udder are freed from milk.

When milking by machine, the apparatus is mounted on a turnstile, and milking cups are attached to the teats. The device creates a vacuum: the milk comes out of the tubules into the container. The cow also needs to be prepared for the process.

The operator must monitor the pressure in the equipment. Standard operating pressure 47 kPa. With low pressure, the milking process takes a long time. It's not effective. With increased pressure, the glasses will compress the cow's teat too much, causing her pain. No air should get into the glass. It will block the milk supply.

Diseases of the cow's udder

One of the common diseases of the udder is mastitis. It can develop due to improper care of the animal, injuries to the gland, or failure to follow milking rules. This is a streptococcal infection. Pathogens enter through the outlet in the nipple, through cracks and wounds. Symptoms vary depending on the type of mastitis. Sometimes it is asymptomatic. The disease can only be recognized after milk testing.

• After calving, a cow most often develops serous mastitis. The udder and nipples become dense and turn red. The iron is hot to the touch. The animal's body temperature may increase: the nose is dry, chewing movements stop. There are white flakes in the milk.
• During lactation, catarrhal mastitis may occur. Small lumps the size of a pea are felt in the udder. The seals quickly increase in size and block the milk tubules. The gland becomes hard. Catarrhal mastitis may appear in one lobe of the udder, while the others remain healthy. The milk acquires a liquid consistency. It separates and flakes are visible.
• The first sign of purulent mastitis is brown clots in the milk. The udder becomes inflamed, and the animal’s temperature rises to 40 degrees. One or all lobes of the gland are enlarged in size and hot to the touch. The outflow of milk stops: all the liquid accumulates in the tubules of the udder. The cow is in severe pain.

To answer the question of how milk is formed, you need to get acquainted with how a cow’s udder works, grows and develops.

Mammary glands are present in mammals of both sexes, but in males they remain underdeveloped, while in females they grow and develop because they are closely connected with her reproductive organs, with the gonads. As the gonads, the ovaries, mature, the mammary glands also grow.

Being skin formations, the mammary glands are related to the sweat glands. It is not for nothing that scientists find a close connection between the milk production of cows and the number of sweat glands in the skin.

In the world of mammals, you can find animals with very simply arranged mammary glands.

In the Australian egg-laying animal platypus, the mammary glands are represented by several dozen tubular glands on both sides of the so-called linea alba. Each tube ends in an excretory duct resembling the duct of a sweat gland. A secretion is released from the duct, which only vaguely resembles milk. It drips from the hair on the mother's abdomen, and the cubs lick it off. The platypus has no nipples.

In marsupials (for example, the Australian kangaroo) there are no cisterns in the mammary glands, but there are nipples through which the baby, being in a pouch on the mother’s belly, sucks milk.

The cow's mammary gland is structured differently. Her udder is formed from the fusion of three pairs of glands, but only the two anterior pairs are normally developed. The third remains underdeveloped. The fifth and sixth teats are quite common in cows, and some milk can sometimes be extracted from them.

The udder of a cow is covered with soft and very elastic, stretchable skin, covered with sparse hair. The more productive a cow is, the thinner the skin on her udder. A significant amount of milk can accumulate in the mammary gland between milkings, and its volume increases by approximately one cup compared to its original value. More than half of the milk yield is located in the udder due to its stretching.

In the udder they distinguish: glandular tissue, consisting of tiny bubbles - alveoli, visible only under a microscope; milk ducts through which milk passes into the milk tanks; blood and lymphatic vessels; nerve fibers.

The structure of the udder can be seen with the naked eye. The section reveals connective tissue in the form of white plates surrounding the glandular part, colored orange-pink. Here there are alveoli and ducts of different diameters.

There are four lobes (quarters) in the udder of a cow - two front and two rear (Fig. 3). If you introduce colored liquid through the nipples, you can make sure that the lobes are not connected to each other by ducts (Fig. 4). This allows you to milk each of them separately. Some diseases of the udder, such as mastitis, usually affect one lobe. That the udder consists of four separate lobes is also evident from the fact that a cow can be completely milked only through all four teats.

The right and left halves of the udder are separated from each other by a subcutaneous elastic septum made of connective tissue, which simultaneously serves as a ligament supporting the udder. As the cow ages, this ligament weakens and the udder sag somewhat (Fig. 5). The same elastic septa divide the mammary gland into separate lobules.

There are a huge number of alveoli in each lobe of the udder. Their internal surface is several square meters (Fig. 6). The alveoli are lined with secretory cells. In large alveoli there are up to hundreds of such cells. Milk is formed in them. The rear quarters of the mammary gland have more alveoli than the front quarters and therefore produce more milk.

The milk formed in the secretory cells passes into the cavity of the alveoli, and from here first into narrow and then into wider ducts, through which it flows into the milk tanks.

Milk cannot leave the alveoli by gravity. It comes only during milking, but we will talk about this later.

Corresponding to the four teats, the udder has four sinuses (cisterns). From 12 to 50 wide ducts open into each of them. The lower section is called the mamillary cistern (Fig. 7). Tanks and ducts are a single system with the same pressure. The tanks can hold 600 milliliters of milk or more. However, in different animals and in different quarters this volume is far from the same. Approximately 40 percent of milk yield is contained in cisterns and ducts, the rest is in the alveoli. In the front quarters, the tanks are usually located on the lateral side, and in the hind quarters, on the back side of the udder. It is useful to take this into account when massaging the udder and milking.

The cavities of the alveoli, milk ducts and cisterns make up a certain capacity of the udder.

The nipple cistern passes below into a narrow and short excretory canal. During milking, it shortens and the teat cistern expands. The excretory canal has a round obturator muscle - sphincter (Fig. 8). The stiffness of the cow depends on the state of the sphincter and its tone (tension). The excretory canal and its obturator muscle also serve as some obstacle to the penetration of bacteria into the nipple.

The skin on a cow's mammary gland is made up of many layers of cells. They fit tightly to the muscles. The skin on the nipples is hairless and does not have sebaceous and sweat glands, so if the udder is poorly cared for, especially on windy summer days, cracks may appear on the nipples.

To get a more complete understanding of how the udder works, you should pay attention to one more circumstance.

The alveoli and thin milk ducts are lined on the outside with special cells (Fig. 6). Their peculiarity is that they have a star-shaped shape and are able to contract. Connected by their processes, the stellate cells form something like a mesh around the alveoli. While the alveoli are filled with milk, the stellate cells stretch, but during milking they contract and squeeze the milk into the ducts. Stellate cells located along the thin ducts, contracting, open these tubules and promote the movement of milk towards the tanks.

If we slaughter a lactating cow, and then remove the udder and make a transverse or longitudinal cut into it, we will be surprised to note that, with the exception of small cisterns, there are essentially no visible cavities in it. Meanwhile, the cow's udder has a significant capacity. A huge number of alveoli, narrow and wide ducts, the tank is able to accommodate a large amount of milk - 15 liters or more. This amount of milk is retained in the udder and does not leak out due to the presence of the obturator muscle in the nipples and the special arrangement of the ducts through which the milk flows into the tank.

What is this feature? The udder can be compared to a sponge that retains water thanks to many narrow tubes that penetrate the body of the sponge in different directions. To squeeze water out of a sponge, a certain amount of force is required. The same applies to the mammary gland, from which milk can be extracted only after compression of the alveoli.

The milk ducts consist of dilations alternating with constrictions in those places where they make their way through the connective tissue partitions between the udder lobules (Fig. 9). In addition, the ducts in the mammary gland connect to each other at different angles. This circumstance alone could explain why the udder is able to hold a relatively large amount of milk. Some scientists also believe that at the mouths of the milk ducts there are thickenings of smooth muscle tissue, similar to the sphincters in the nipples.

Finally, keep in mind that as milk accumulates, the channels in the udder are able to relax and accommodate the resulting milk.

As the reader can see, the structure of the udder helps to retain the milk accumulated in it, but it also makes milking it difficult.

And yet the mechanism we are describing is said to “fail”; in some cows, milk involuntarily flows out of the tank through the teats. This is usually a consequence of weakness of the nipple sphincter.

Blood vessels of the udder

The mammary gland is rich in blood vessels. The richer it is in blood and lymphatic vessels, as well as nerve plexuses, the more milk is produced in it (Fig. 10). Each alveolus is surrounded by a dense network of capillaries (tiny blood vessels). Approximately 3.5 liters of blood flows through the udder of a lactating cow in one minute, and four times less in a dry cow. The blood vessels in the mammary gland are able to quickly pass blood. After all, to produce one liter of milk, at least 400 liters of blood must pass through the udder. That is why there is a direct connection between the productivity of the cow and the development of the arterial vessels of the udder. In old cows with reduced milk yield, the number of small arteries in the udder is significantly reduced.

As you know, blood flows through the arteries to the mammary gland, and through the veins it flows away from it and returns to the heart. The arteries run deep in the animal's body and, with some exceptions, cannot be seen or felt. Veins lie more superficially. In a dairy cow, powerful blood vessels can be observed on the udder and belly (Fig. 11). These are the external genital and saphenous abdominal veins. The perineal veins are less developed. The significant size of the saphenous abdominal veins often corresponds to the high productivity of the cow, which is why they are (not entirely correctly) called milk veins. However, the width of the veins largely depends on the month of lactation: during the period of highest milk yield after calving, a huge amount of blood is drained from the udder.

Speaking about the circulatory system of the udder, it is necessary to point out two important points. Between some veins there are connecting bridges through which blood from one vein can pass to another. The second remark concerns the perineal arteries and veins. Leningrad scientists I. I. Grachev and A. D. Vladimirova managed to discover that blood through the perineal vein does not flow from the gland, but towards the mammary gland, from the area of ​​the gonads. Perhaps thanks to this, the mammary gland receives sex hormones important for its development in a shorter way (p. 47).

The more branched the network of blood vessels is on an organ, the better it is supplied with nutrients and oxygen. This occurs through the lymph and tissue fluid surrounding the breast cells.

In many cows, after calving (sometimes before it), even swelling of the udder is observed. This is caused by the accumulation under the skin of significant amounts of lymph, which at this time does not have time to flow away from the udder (Fig. 12). The skin on the udder thickens significantly, but the tissue the mammary gland itself - the alveoli and ducts - the swelling does not spread. However, the swelling interferes with the normal functioning of the mammary gland. This disorder in the skin goes away faster after massaging the organ. Therefore, milking with udder massage is a must-have remedy for combating postpartum mammary gland edema.

Nervous system of the udder

The mammary gland is a very sensitive organ. In the skin of the udder and on the nipples, as well as around the alveoli, there are many different sensory nerve endings - receptors. They perceive irritations arising in the mammary gland and transmit them to the brain. Some receptors perceive chemical irritations, others - pressure and pain, and others - temperature differences. The animal's nipples are especially sensitive (Fig. 13). Some scientists rightly claim that in terms of sensitivity, cow nipples differ little from human fingers.

From the spinal cord, several nerve trunks approach the udder, branching here into tiny threads through which signals from the central nervous system arrive to the organ. These nerves are important for growth, udder development and milk production.

Good udder

Large milk yields can be obtained for a long time from cows whose hearts, lungs and digestive organs are capable of processing large amounts of feed, in other words, from cows with good health. But there is no doubt that the key to high milk yield is a good udder, rich in glandular tissue.

Many scientists attach great importance to the shape of the udder. What are the characteristics of a good udder?

Although a large udder does not always indicate high milk yield, if a cow has a small udder, then, as a rule, it is impossible to obtain high productivity from her. A good udder is of sufficient depth and length. Depth is the distance from the base of the nipples to the belly. The length is measured in three directions: from the place of attachment of the udder in front to the front nipples; then the distance between the front and rear nipples; finally, the distance from the rear teats to the point where the udder is attached at the back.

As the American scientist Gerner notes, the udder is assessed by capacity, shape, length, width and depth. Cows with cup-shaped rather than round udders will be more productive. A good udder protrudes forward, it is firmly attached to the body and does not sag. The posterior attachment is high and wide (Fig. 14), the udder lobes are even and symmetrically located. To the touch, such an udder is soft, flexible, elastic, falls off after milking, and has long, convoluted, clearly defined veins. The nipples are of the same size and moderate length - on average 8-10 centimeters, and in diameter - 2-3 centimeters. They have a cylindrical shape, are directed vertically and allow milk to pass freely.