To answer the question of how milk is formed, it is necessary to get acquainted with how it works, how the udder of a cow grows and develops.
The mammary glands are present in mammals of both sexes, but in males they remain underdeveloped, while in the female they grow and develop, because they are closely connected with her reproductive organs, with the sex glands. As the ovaries mature, so do the mammary glands.
Being skin formations The mammary glands are related to the sweat glands. No wonder scientists find close connection between the milk production of cows and the number of sweat glands in the skin.
In the world of mammals, one can meet animals with very simply arranged mammary glands.
In the Australian oviparous platypus, the mammary glands are represented by several dozen tubular glands on both sides of the so-called white line of the abdomen. Each tubule ends with an excretory duct, resembling the duct of a sweat gland. A secret is released from the duct, only remotely resembling milk. It drips from the hair on the mother's abdomen and the young lick it off. The platypus has no nipples.
Marsupials (for example, the Australian kangaroo) do not have cisterns in their mammary glands, but they have nipples through which the baby, being in a bag on the mother's belly, sucks out milk.
The mammary gland of a cow is arranged differently. Her udder is formed from the fusion of three pairs of glands, but only the two front pairs are normally developed. The third one remains underdeveloped. The fifth and sixth nipples are quite common in cows, and some milk can sometimes be extracted from them.
The udder of a cow is dressed in soft and very elastic, extensible skin, covered with sparse hair. The more productive the cow, 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 about one warm compared to the initial value. More than half of the milk is placed in the udder due to its expansion.
In the udder, there are: glandular tissue, consisting of the smallest vesicles - alveoli, visible only under a microscope; milk ducts, through which milk passes into the milk tanks; circulatory and lymphatic vessels; nerve fibers.
The structure of the udder can be seen with the naked eye. Visible on cut connective tissue in the form of white plates surrounding the glandular part, painted in orange-pink color. Here are the alveoli and ducts of different diameters.
There are four lobes (quarters) in the cow's udder - two anterior and two posterior (Fig. 3). If you enter a 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. In some diseases of the udder, such as mastitis, one lobe is usually affected. 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 of connective tissue, which at the same time serves as a ligament supporting the udder. With the age of the cow, this ligament weakens and the udder sags somewhat (Fig. 5). The same elastic partitions divide the mammary gland into separate lobules.
Alveoli in each lobe of the udder great amount. Their inner surface is several square meters(Fig. 6). The alveoli are lined with secretory cells. Large alveoli contain up to hundreds of such cells. They produce milk. The posterior quarters of the mammary gland have more alveoli than the anterior 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 from the alveoli cannot go by gravity. It comes only during milking, but we will talk about this later.
Corresponding to the four teats, there are four sinuses (cistern) in the udder. In each of them, from 12 to 50 wide ducts open. The lower section is called the teat cistern (Fig. 7). Tanks and channels are a single system with the same pressure. Tanks can hold 600 milliliters of milk or more. However, in different animals and in different quarters, this volume is far from being the same. Approximately 40 percent of milk is contained in tanks and ducts, the rest is in the alveoli. In the fore quarters, the cisterns are usually located on the lateral side, while in the hind quarters, on the back side of the udder. This is useful to consider 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 - the sphincter (Fig. 8). The stiffness of the cow depends on the state of the sphincter, 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 the teats of a cow's mammary gland is made up of many layers of cells. They are tight to the muscles. The skin on the nipples is devoid of hair and has no sebaceous and sweat glands, therefore, with poor udder care, especially on windy summer days, cracks may appear on the nipples.
To get a more complete picture of how the udder is arranged, one more circumstance should be paid attention to.
The alveoli and thin milk ducts are lined on the outside with special cells (Fig. 6). Their peculiarity lies in the fact that they have a star shape and are able to contract. Connecting with their processes, stellate cells form something like a grid around the alveoli. While the alveolus is filling with milk, the stellate cells stretch, but contract during milking and squeeze the milk into the ducts. The stellate cells located along the thin ducts, contracting, open these tubules and promote the movement of milk towards the cisterns.
If a lactating cow is slaughtered, and then the udder is removed and a transverse or longitudinal section is made in it, we will note with surprise that, with the exception of small tanks, there are essentially no visible cavities in it. Meanwhile, the udder of a cow has a significant capacity. A huge number of alveoli, narrow and wide ducts, tanks are able to accommodate a large number 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 due to the many narrow tubes that penetrate the body of the sponge in different directions. It takes a certain amount of force to squeeze water out of a sponge. The same applies to the mammary gland, from which it is possible to extract milk only after compression of the alveoli.
The milk ducts consist of dilations alternating with constrictions where they make their way through the connective tissue septa between the udder lobes (Fig. 9). In addition, the ducts in the mammary gland are connected 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, in addition, believe that at the mouths of the milk ducts there are thickenings of smooth muscle tissue, like sphincters in the nipples.
Finally, it should be borne in mind that as milk accumulates, the channels in the udder are able to relax and accommodate the resulting milk.
As the reader sees, the structure of the udder helps to retain the accumulated milk in it, but it also makes it difficult to milk it out.
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 due to 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 formed in it (Fig. 10). Each alveolus is surrounded by a dense network of capillaries (the smallest blood vessels). Approximately 3.5 liters of blood flows through the udder of a lactating cow in one minute, in a dry cow - four times less. Blood vessels in the mammary gland are able to quickly pass blood. Indeed, for the formation of one liter of milk, at least 400 liters of blood must pass through the udder. That is why there is a direct relationship between the productivity of a cow and the development of udder arteries. In old cows that reduce milk yield, the amount of small arteries in the udder.
As you know, arteries blood is coming to the mammary gland, and flows from it through the veins and returns to the heart. The arteries run deep in the animal's body and, with a few exceptions, cannot be seen or felt. The veins lie more superficially. In a dairy cow, powerful blood vessels can be observed on the udder and on the belly (Fig. 11). These are the external genital and saphenous abdominal veins. Less developed perineal veins. The significant size of the saphenous abdominal veins often corresponds to the high productivity of the cow, so they are (incorrectly) 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 udder circulatory system, it is necessary to point out two important points. Between some veins there are connecting bridges through which blood from one vein can pass into another. The second remark concerns the perineal arteries and veins. Leningrad scientists I. I. Grachev and A. D. Vladimirova managed to discover that the blood through the perineal vein flows not from the gland, but towards the mammary gland, from the area of the gonads. Perhaps because of this, the mammary gland receives the sex hormones important for its development in a shorter way (p. 47).
The more branched the network of blood vessels on the organ, the better it is supplied with nutrients and oxygen. This occurs through the lymph and interstitial 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 of significant amounts of lymph under the skin, which at this time does not have time to flow from the udder (Fig. 12). The skin on the udder is significantly thickened, but on the tissue the mammary gland itself - alveoli and ducts - edema does not spread. normal operation mammary gland. This violation in the skin passes faster after organ massage. Therefore, milking with udder massage is a mandatory tool to combat postpartum mammary edema.
The nervous system of the udder
The mammary gland is a very sensitive organ. In the skin of the udder and on the teats, as well as around the alveoli, there are many different sensitive nerve endings - receptors. They perceive irritations that occur in the mammary gland and transmit them to the brain. Some receptors perceive chemical irritations, others - pressure and pain, and others - temperature differences. An animal's nipples are especially sensitive (Fig. 13). Some scientists from with good reason they say that in their sensitivity the nipples of a cow differ little from the fingers of a person.
Several nerve trunks approach the udder from the spinal cord, branching here into tiny threads, through which signals from the central nervous system come to the organ. These nerves are great importance for growth, udder development and milk production.
good udder
Large milk yields can be obtained for a long time from cows whose heart, lungs and digestive organs are able to process large feed dachas, in other words, from cows with good health. But there is no doubt that the guarantee of high milk yields 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 yields, nevertheless, if a cow has an udder that is not roomy, then, as a rule, high productivity cannot be obtained from it. A good udder is deep and long enough. 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 teats; then the distance between the anterior and posterior nipples; finally, the distance from the hind teats to the point of attachment of the udder at the back.
As the American scientist Gerner notes, the udder is evaluated by capacity, shape, length, width and depth. More productive will be cows with cupped udders rather than round udders. A good udder protrudes forward, it firmly adjoins the body, 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, subsides after milking, has long, tortuous, distinct veins. Nipples of the same size and moderate length - an average of 8-10 centimeters, and in diameter - 2-3 centimeters. They have a cylindrical shape, are directed vertically and freely pass milk.
On the intensive work One of the most amazing in terms of structure and function of the organ in animals is being built the most important branch of animal husbandry - dairy cattle breeding. Such an organ is the mammary gland or udder.
The mammary gland of the female of any kind of animal consists of glandular tissue, which produces milk, as well as connective and adipose tissues that protect and support the glandular tissue, supplied with blood and lymphatic vessels, nerves. The glandular tissue consists of cells that form the so-called alveoli, united by connective tissue into lobules, but appearance similar to grapes. Blood with nutrients in large quantities enters the glandular cells, where milk is formed, which constantly flows into the lumen of the alveoli. The alveoli are united by thin tubules, which then merge into larger ducts, ending in cisterns where milk is collected. Milk is excreted from the tanks through the nipples (Fig. 94).
In cows, connective tissue partitions divide the udder into two halves: right and left. Each half, in turn, is divided into two parts (lobes): anterior and posterior. Thus, the udder of a cow has four quarters (lobes), which pass into the teats without sharp boundaries. Each nipple at the base has an expansion in the form of a tank, and the top ends with one opening closed by the sphincter.
The skin of the udder is covered with sparse delicate hairs. On the posterior quarters of the organ, the hairs are directed from below upwards and, meeting the reversely directed hairs of the surrounding parts, form a noticeable line that limits and determines the size and shape of the "milky mirror". In richly dairy cows, the milk mirror is well developed (Fig. 95). The udder of lactating cows together with milk can weigh up to 50 kg.
The distribution of feed, the noise of operating milking equipment, and especially proper massage glands, cause reflex hyperemia of the udder and an increase in internal pressure around the alveoli, which leads to the most active milk secretion, and the release of the udder from milk contributes to the secretion of milk.
Milk owes its name to the highest class of animals - mammals. Of all the variety of mammals, man has tamed, domesticated and has long been using only a few species: cows, goats, sheep, horses, buffaloes, camels. Milk from some animals he uses for food, from others - for medicinal purposes. Ho, of course, cow's milk has received the main mass distribution throughout the world.
It is no coincidence that in the ancient Persian book Zend-Avesta, revered as sacred, it says: “In cows is our strength, in cows is our food, in cows is our victory.” An old saying of the Watussi African tribe says: "Except for the king, there is nothing higher than a cow." In India, even today, the cow is considered sacred, inviolable. It is proved that for the first time a person felt the taste of cow's milk more than 5 thousand years ago. The cow and at the present time - without any exaggeration - the breadwinner of mankind.
Cow's milk is white or slightly yellowish color and sweet taste. The chemical composition of milk is complex. It contains the components necessary for human nutrition: proteins, fats, carbohydrates, acids, hormones, vitamins, minerals (C, K, Ca, Mg, etc.), microelements, water (Table 10).
Milk is considered normal if obtained from healthy cows 6-10 days after calving. Lactation lasts 300 days, and during this time, depending on the breed, conditions of detention, feeding, it can vary from 2 to 14 thousand kg. The lactation period in infertile and castrated cows after calving is significantly lengthened. A case is known when a castrated cow was milked for 7 years and during this time gave more than 20,000 liters of milk.
The chemical composition of milk is not constant. Even in the same animal, depending on age, season, feeding conditions and other factors, the fat content most often changes. So, in the evening milk yield is less fat than in the morning. When milking milk, the first portions of fat contain less than at the end of milking.
The structure of the mammary gland in a yachikha is similar to that of a cow, but milk production is much lower.
Dairy pits for 225 days give 650-700 liters of milk with a fat content of 5.3-8.6%. Maximum milk yield 1060 l. By palatability Yachiha milk is much better than milk from other domestic animals.
The mammary gland of a mare, a donkey during the dry period decreases so much that it almost completely merges with the skin of the abdomen. It consists of two halves, each of which has separate alveoli, excretory ducts, merging at the base of the nipples into two or three cisterns. Each tank communicates with external 2-3 channels. Therefore, at the top of the nipple there are holes corresponding to the number of channels.
Despite the small volume of the udder, mares are characterized by high milk production. It is believed that up to 2600-2800 ml of milk can accumulate in the capacitive system of the udder of mares, and up to 30 liters per day. Lactation in most mares lasts 6-8 months, and sometimes more. Non-pregnant mares can feed their young for 2 or even 3 years.
According to the physical and chemical properties, the milk of mares and donkeys is characterized by a high content of sugar and vitamins. The fat of the milk of these animals consists of balls smaller than in cow's milk. Therefore, in room conditions it has a semi-liquid, vaseline-like consistency. It is almost impossible to knock down butter from the milk of mares and donkeys.
The mammary gland of a camel has four lobes and is divided into right and left halves, anterior and posterior lobes (like in a cow). The shape of the udder is hemispherical, with sparse thin hairs on pigmented Skin. The hind quarters are more developed than the fore quarters. Each lobe is provided with a conical nipple. The capacitive system of the mammary gland of a camel is small, which makes it necessary to milk this animal more often.
The milk productivity of two-humped camels (bacterians) is lower than that of one-humped camels (dromedaries), and ranges from 769 to 1716 liters of milk. The daily milk yield of dromedaries can be 15-20 liters. The duration of lactation averages 13-14 months.
Dromedary milk is bright white, without shades, regardless of the amount of fat in it, the consistency is homogeneous and thick, there is no smell, the taste is sweet. Bacterian milk tastes more insipid. Camel milk contains a lot of sugar (up to 6.3%), mineral salts, and vitamins. By content ascorbic acid inferior only to the milk of mares,
The mammary gland of a sheep and a goat consists of two halves, clearly demarcated by an inter-udder groove. In a sheep, the udder lobes are rounded, with short teats, while in a goat, the udder has cone-shaped teats, is more mobile, sags strongly and is subject to mechanical damage.
Sheep milk is 2 times fatter than cow's milk, therefore, when recalculated by fat content, their milk yield can reach 2566 kg of cow's milk. The specific taste and smell of sheep's milk is due to the high content of caprylic and capric acids. Lactation, depending on the breed and conditions of keeping animals, lasts from 5 to 8 months.
Goat milk is characterized high content albumin, casein and important mineral salts, which makes it related to human milk. There are a lot of historical examples when orphans who were left without a mother after birth for various reasons were fed with goat's milk.
Protein, glucose and lactose (milk sugar) of goat's milk are easier to digest, fat globules are smaller, distributed throughout the mass of milk and easily absorbed by the intestinal walls. The high nutritional value of milk is due not only to a good amino acid composition, but also to a high content of phosphorus, cobalt, vitamins A, E, C and group B. Fresh goat milk can be consumed immediately after milking, as goats do not suffer from tuberculosis. It is especially useful for sick, debilitated children suffering from gastrointestinal diseases. The use of goat's milk has a beneficial effect on metabolic disorders.
The systematic use of goat's milk prolongs the vital activity of a person, delays the aging of the body. Goat milk treats serious illness, like Graves' disease (goiter) - enlargement of the thyroid gland.
Goat's milk is extremely beneficial for people who are allergic to cow's milk or other foods. A certain therapeutic effect when drinking goat milk is noted for diseases such as eczema, bronchial asthma, migraine, colitis, hay fever, stomach ulcers, digestive tract disorders, liver diseases, gallbladder, as well as symptoms caused by a stressful situation, such as insomnia. , constipation and indigestion. In addition, it has been observed that goat's milk in the second half of a person's life is effective tool against arteriosclerosis.
Goat milk is used both whole and for the preparation of various products. Various cheeses are prepared from it, and first of all, Roquefort, Swiss cheese, cheese, as well as butter, yogurt. AT Central Asia kurut cheese is prepared from buttermilk by evaporation - a very healthy and nutritious product with a long shelf life. Some breeds of goats give up to 1000 liters of milk per lactation.
The mammary gland of a pig consists of 8-16 (sometimes up to 20) glandular lobes, located in the form of packages on both sides of the white line. Each gland has an underdeveloped milk cistern, which opens at the top of the nipple with a nipple canal. There are as many channels in the nipple as it unites the mammary glands (usually 2-3). It is generally accepted that the more channels in the nipple, the more active the mammary gland functions. The anterior mammary glands are more developed than the posterior ones.
Pig farmers believe that the greater the sow's own body weight and the number of live piglets in the litter, the higher her milk production. A pig gives an average of 3-4 liters of milk per day, sometimes up to 8 liters. During lactation (56 days), pigs produce about 297 liters of milk. Piglets suckle the uterus 4-17 times a day, and each newborn receives 25-50 ml of milk for the first sucking.
In pigs, unlike other mammals, the milk ejection reflex is manifested in a special way. So, if after childbirth it is carried out even from one touch of the piglet to the nipple, then later milk secretion occurs only in that nipple that directly irritates the piglet.
Pig's milk in terms of physical and chemical composition differs markedly from the milk of other animals. Pig milk is a white, sticky, sweetish liquid with a characteristic odor and is capable of long time keep fresh.
The female reindeer has four mammary glands that form a compact udder. Each gland has its own nipple. On the skin of the udder is thick hairline, including on the nipples, which protects against low temperatures. The udder is small in size, and its weight is no more than 350 g. The hind lobes are not only more developed, but they also form 70-80% of all milk. Interestingly, the fat content of milk from the back half of the udder is 15-16% higher than from the front half.
Reindeer lactation lasts an average of 5-6 months (May-October). Milk yield for lactation is 30-55 liters of milk. The average daily milk yield of productive females reaches 500-600 ml.
Reindeer milk is very rich in fat and protein, but poor in sugar; in appearance it resembles cream, has a yellowish color, viscous consistency.
The udder of the moose cow, like the female reindeer, consists of four mammary glands, each of which has its own nipple. The shape of the udder is flat. The udder is covered thick hair. Each nipple has its own little developed cistern.
Lactation in moose cows lasts 4-6 months. An interesting fact is noted: the fat content of milk is always higher in the half of the udder that was milked first. With machine milking, moose cows always contain less fat in milk than with manual milking. However, due to the characteristics anatomical structure and the location of the teats, the use of machine milking of elk by existing milking machines without their modernization is very problematic.
Colostrum is a kind of secret of the mammary gland. It has a yellowish, brown or even sometimes red color, a peculiar smell and a salty taste. Colostrum is separated in the first 6-10 days after calving. Colostrum contains 10 times more vitamins A and E than milk, 3 times more vitamin B, more mineral salts, especially Ca, Mg, the laxative effect of colostrum on the latter depends on the latter. newborns.
Of particular value in colostrum are whey proteins - globulins and albumins. Immune globulins increase the resistance of the newborn against many diseases, and their value is extremely important.
Until the 3-4th day, there is an increased content of proteins in colostrum, which are very easily absorbed by newborns compared to milk casein.
When the udder is fully milked, its contents stabilize from the 4-5th day and do not differ from ordinary milk. When the udder is not fully milked, the colostrum is released up to 10-12 days.
It has been proven that colostrum is not a specific secret of the mammary gland, but ordinary milk, formed earlier and converted by the gland into colostrum during a long stay in the capacitive system of the gland.
It is important to know: if the animal was not determined at launch, milked before childbirth, then colostrum will never be formed.
The mammary glands begin to develop in the embryos of cattle, sheep, horses from the epithelium of the skin and mesenchyme on the abdominal wall in the region from the umbilical cord to the pubic region, in the embryos of pigs and dogs - from the sternum to the pubic region. Epithelial cells multiply and longitudinal thickenings form on the skin on the right and left sides of the medial sternal groove and from the linea alba. These thickenings are called milk strips, rollers. Later, in prefetuses, milk lenses are clearly marked on the milk ridges in the form of rounded thickenings of the epithelium of the skin and the mesenchyme underlying it.
The number of milk lenses is equal to the number of lobes of the mammary glands with nipples in a given animal species. In prefetuses and fetuses, parts of the mammary glands develop from milk lenses.
The epithelium of milk lenses forms an outgrowth in the subcutaneous layer in the form of a cone. At the end of this epithelial outgrowth, tree-like outgrowths of the epithelium arise. Around them, a connective tissue framework is formed from reticular, loose and adipose connective tissue. Inside the epithelial flask, a slit-like cavity of the nipple and milk cistern arise. The center of the epithelial flask rises along with the skin covering it and forms the nipple. These parts of the rudiments of the mammary glands are expressed in the fetal period of development in heifers at the fourth month, in pigs at the end of the second month. Subsequently, until birth, the growth of new epithelial tree-like outgrowths occurs. The amount of adipose, reticular, loose connective tissue increases.
In a newborn heifer, the udder has relatively developed nipples and an undeveloped body. Each lobe has a cistern and milk ducts, from which strands of epithelial tissue come, surrounded by loose connective, reticular, and adipose tissues. In place of future alveolar tubes, there are microscopic thickenings of epithelial tissue.
Heifers aged 12-15 months have an udder body and teats; the body of the udder is relatively undeveloped. Separate alveoli and alveolar tubes appear at the ends of the epithelial strands of the ducts.
At 2-3 months of pregnancy, the number of alveoli and alveolar tubes in the lobules begins to increase. At 7-8 months of pregnancy, there is an increased development and growth of the glandular tissue of the udder. Before calving, the epithelium of new alveolar tubes multiplies, blood circulation in the udder increases, and colostrum secretion begins. The udder increases in volume, the secretion of colostrum begins, the intensive secretion of which continues for a week after calving and then is replaced by the secretion of milk.
During the dry period (cessation of lactation before calving), the total volume of the udder decreases, a significant number of blood capillaries subside. A significant part of the alveolar tubes and ducts is filled with leukocytes and a mass of cytoplasm of dying epithelial cells. Fall down inside and interlobular ducts. The thickness of the layers of loose, reticular and adipose tissues inside the lobes and in the lobules of the mammary gland increases by 2-3 times. Before calving, blood circulation in the udder increases, the epithelium of the alveoli in the lobules regenerates, the udder increases in volume. Colostrum secretion begins.
In pigs after farrowing, those lobes of the mammary gland, the nipples of which the piglets suckle, develop, increase in volume, the rest increase slightly.
Breed features of the structure of the mammary glands are manifested in the volume, shape of the udder and the quantitative ratios of the glandular and connective tissue inside the lobes of the glands. In cows of meat breeds, which give 800-1000 liters of milk per season, the udder of a primitive, flat or goat form prevails, the glandular tissue in the lactating udder occupies half the mass of the share. In dairy cows with a milk yield of 3-5 thousand liters of milk per year, the glandular tissue makes up 2/3-3/4 shares of the udder, the bowl-shaped or bath-shaped udder prevails.
Milk is a white liquid that contains small particles of fat, lactose, vitamins, and minerals. It is produced in the mammary glands of a cow. The quality of milk depends on the nutrition of the animal, the conditions of detention, the age of the individual, the time of year. All the nutrients that are in milk get into it from the blood. Features of the anatomy of the mammary gland of a cow contributes to the development of useful nutrient product necessary for both children and adults.
Features of the anatomical structure of the udder
The udder of a cow 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 with a nipple. The anterior glands are smaller in volume than the posterior ones, but in dairy cows all lobes are the same in volume.
The udder has a sheath of connective tissue, which is covered with hairs. The fabric is gathered into elastic folds. They are smoothed out as the milk lobes are filled 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, so there is more milk in them. Nerve fibers react to pressure, temperature changes, chemical stimulus;
- excretory canals connect the alveoli to the milk cistern, a cavity in which milk accumulates. Each tank can store up to 500 ml. liquids;
- there is an exit from the tank - the teat channel. Milk is being pumped out through it. The nipple cavity holds 40 ml of liquid. Its inner wall is glandular, the outer one consists of smooth fibers. The nipple has no hair. It protects the milk channel from external influences, infections. At the same time, the nipple is designed to remove milk from the gland;
- each lobe has its own system for connecting the alveoli and milk ducts.
The function of the udder is to produce and release milk. The volume of the bowl reaches 40 kg. With weakened ligaments, it sinks under the weight or deforms. Most often, changes are due to the age of the cow, the number of calving.
Nipples do not have sebaceous glands. During the hot period, cracks may appear on it. They cause pain to the cow when in contact with grass or during milking. Nipples need care. After each milking, they are smeared with a nourishing cream.
The shape of the udder is not the same for different breeds of cows. In dairy breeds, which are distinguished by good productive qualities, the gland has an elongated bath shape. It is located along the abdominal cavity. Dairy-meat breeds most often have a bowl-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.
Production of milk in the udder of a cow
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 the pregnancy of the individual and after calving. Lactation is caused by prolactin, which is released from the anterior pituitary gland. The hormone stimulates the growth of the gland, and prepares it for lactation. The alveoli contain lactocytes. These are the cells that produce milk from blood elements.
The fluid in the alveoli begins to be produced even before the birth of the calf. It is whitish in color, salty in taste, viscous and thick. It's colostrum. The calf after birth sucks out 1.5 kg of nutrient fluid in the first hours. He captures the nipple with his lips and thereby triggers the mechanism of the nerve impulse. 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 given out, leaving the shares empty. After 4 hours, they will again be filled with liquid. It is recommended to milk cows every 6 hours. When the work of the mammary glands returns to normal, milking is carried out every 12 hours. If this period of time is exceeded by 1-2 hours, the animal will have less milk. Over time, it will cease to be produced.
The development of the mammary gland in cattle occurs before 6 calving. After 9 calving, the milk production function begins to decrease. The cow is getting old. In dairy breeds, lactation can continue until 13-16 calving. Milk acquires its qualities, ceases to resemble colostrum, 2 weeks after calving. The lactation period lasts 300 days. During this time, the animal can give up to 16 thousand kg of milk.
cow milking process
Before you start milking a cow, you need to prepare both the room and the animal. The stall is cleaned, 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 sees the milkmaid. An enamel bucket is used as a container for milk.
The cow loves affection, it is necessary to stroke it and talk to it in a calm voice. To keep the animal calm, it is tied to a turnstile. The tail is lightly tied to the leg with a whip. In order for the pituitary gland to release oxytocin into the body, and the production of milk begins, it is necessary to massage the cow. This is a kind of imitation of the actions of a calf during feeding, which taps the nurse's udder with its head. Perform diagonal and horizontal strokes, circular movements of the hands along the 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 has increased in size, the milking process begins.
The nipple is slightly captured in a fist: the thumb and forefinger are at the base of the nipple, on the same level. The little finger is located at the exit of the nipple tubule. The remaining fingers hold the body of the nipple strictly vertically. Squeeze the base of the nipple and squeeze the milk out of the tubule with your fingers.
The first drops are squeezed into a clean mug. The color of milk is determined: whether there are any impurities. With the first portion, bacteria and dirt come out of the nipple if the cow was not washed well. The rest of the milk is put into a container. After making the first cycle of finger movements, they wait until the nipple is filled again. Usually it takes 2-3 seconds. In a similar way, all 4 lobes of the udder are released from milk.
With machine milking, the apparatus is fixed on a turnstile, and teat cups are attached to the nipples. 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. Under reduced pressure, the milking process takes a long time. He's not efficient. With increased pressure, the cups will compress the cow's nipple too much, causing her pain. Air must not enter the glass. It will block the flow of milk.
Diseases of the udder in cows
One of the most common diseases of the udder is mastitis. It can develop with improper care of the animal, with injuries to the gland, with non-compliance with the rules of milking. It's a streptococcal infection. Pathogens enter through the exit in the nipple, through cracks and wounds. Symptoms vary depending on the type of mastitis. Sometimes it is asymptomatic. The disease can be recognized only after milk tests.
- After calving, the cow most often develops serous mastitis. The udder and nipples become dense, acquire a red color. The iron is hot to the touch. The animal's body temperature may rise: the nose is dry, chewing movements stop. Milk has white flakes.
- During lactation, catarrhal mastitis may occur. Small seals, the size of a pea, are felt in the udder. Seals quickly increase in size, block the milk tubules. The gland becomes hard. Catarrhal mastitis may appear in one part of the udder, while others remain healthy. Milk becomes liquid. It exfoliates, flakes are visible.
- The first sign of purulent mastitis is brown clots in the milk. The udder becomes inflamed, the animal's temperature rises to 40 degrees. One or all lobes of the gland are enlarged, 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 prevent the development of the disease, colostrum is taken for analysis in the first days after calving. Research is carried out in the laboratory or at home. For home testing use a rapid test. A 5% solution of dimastine is added to milk: it is purchased in pharmacies. If the color of the milk has not changed, then there are no streptococci in it. Even with small changes in the shade of milk, additional tests are carried out in laboratories.
Cow mammary anatomy
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Structure of a cow's udder
The milk productivity of a cow depends on many different factors, such as breed, age and health of the animal, lactation period, etc. Equally important is the shape and size of the cow's mammary glands, the presence of visible milk passages on them. By the appearance of the mammary gland, an experienced animal husbandry specialist can determine whether a cow has a high milk yield or belongs to a meat direction with a low milk yield.
Location and structure of the udder
The mammary glands of a cow are called the udder. The udder divides into four mammary glands, forming the right and left side. The parts are divided among themselves by a middle partition. In turn, each half is formed by two lobes, in which there are ducts for removing milk. The lobes end in nipples and they do not communicate with each other. This feature of the structure must be taken into account when milking cows. An important point is the release of milk from all parts of the udder, since it cannot get from one to another.
The udder is located in the pelvic region of the cow and is firmly attached to the connective tissue and a whole set of suspensory ligaments. The supporting partition separating the right and left parts of the udder becomes less strong with the age of the cow and the udder tends to sag.
Tissues that make up the udder of a cow
Three types of tissues are involved in the structure of the udder. These are glandular, adipose and connective tissues.
The glandular tissue is formed by many tiny follicles called alveoli. Them inner part lined with milk-producing cells. Flowing out of the alveoli, the milk passes through the thinnest ducts, which are connected to the channels. From the milk canals, it enters the large milk passages, and then into the ducts that communicate with the milk tanks. The tanks themselves end in a nipple with a channel in the middle for removing milk. To prevent the uncontrolled flow of milk, this channel has a ring of muscles at the end, called the sphincter. During milking, the sphincter relaxes the contraction and allows milk to be extracted.
Adipose and connective tissues perform protective functions for the alveoli. The connective tissue is a kind of supporting apparatus, it is located directly around the glandular tissue, protecting it from adverse external influences. It is literally permeated with many lymphatic and blood vessels, nerve endings that transmit to the central nervous system various irritations. It is the connective tissue that separates the udder into separate parts.
1 - nipple; 2 - milk ducts; 3 - nerves; 4 - sphincter; 5 - milk tank;
6 - connective tissue; 7 - alveoli; 8 - vein; 9 - artery.
Rice. Structure of a cow's udder
Outside, the entire surface of the udder is covered with elastic skin with short soft hairs. In adult cows with high milk yields, this skin is thin and smooth.
Milk formation process
To launch such complex process, like milk formation in the body of a cow, in addition to the work of the mammary gland itself, the functioning of other systems and organs is also necessary. Thus, nutrients delivered to the cow's udder through the pudendal artery and vein take an active part in the production of milk. Blood circulation through blood vessels and capillaries occurs both from the base of the udder to the teats, and from one part of the udder to another. The lymphatic system assists in the movement of fluid through the udder. At the base of the udder on each side are lymphatic glands, to which it supplies fluid.
The hormone prolactin, which is secreted into the blood and causes increased milk production, is important for the amount of milk. Warm touching or sucking on the teats by the calf irritates the nerve endings at the tips of the udder. It also releases a hormone that promotes milk production.
It is worth noting that the milk-producing cells in the alveoli also synthesize proteins and fats into it from the nutrients that come with the blood.
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Structure of a cow's udder
The structure of the mammary gland, the formation of milk
The udder of a cow is the mammary gland. It consists of four shares - quarters: two front and two back. The udder lobes do not communicate with each other, and therefore milk from one udder cannot get into others. Each share of the udder has its own teat.
The left and right halves of the udder are separated by an elastic partition, which not only separates the mammary gland, but also supports it. In older cows, it weakens, and therefore, with age, the udder becomes more pendulous.
The udder consists of glandular, adipose and connective tissues, each of which performs its own functions. The formation of milk occurs in the glandular tissue, which consists of a large number of tiny bubbles - alveoli. The inner surface of the alveoli is lined with cells in which milk is formed. The milk accumulated in the alveoli enters the smallest milk ducts, which connect into the milk ducts, which enlarge as they merge and form the milk ducts. Through even wider milk ducts, milk enters four milk tanks. Each tank ends with a teat section of the tank. An excretory canal is located in the nipple, which at the end has a circular muscle - a sphincter that prevents the spontaneous removal of milk to the outside. During milking, the sphincter relaxes, allowing milk to be drawn from the udder.
By the time of milking, the tanks contain up to 25% of the milk accumulated in the udder, and the rest is in the ducts and alveoli. If a catheter, which is a hollow tube, is inserted into the udder teat, then the cisternal milk will spontaneously flow out. However, complete emptying of the udder can only be achieved by milking.
The connective tissue in the udder is located around the glandular tissue, performing a supporting function and protecting the udder from adverse effects. external environment.
The udder has many sensitive nerve endings that transmit signals of irritation to the central nervous system, for example, the start of milking, etc.
Outside, the udder is covered with elastic skin with sparse short hair. Therefore, under adverse environmental influences, poor care, dampness and drafts in the room, the rapid movement of cows, it is easily damaged, which can cause mastitis. In high-yielding cows, the udder skin is thinner and more elastic. On this basis, one can judge the productive qualities of a cow.
Before milking, the udder falls and many folds form on it, especially on the back side. This is the so-called udder reserve, by the severity of which one can judge the capacity of the mammary gland.
Young cows have a more developed capacitive system of the udder, which should be taken into account when organizing their milking. The growth and development of the glandular tissue continues until the 6-7th lactation, and then, as the body ages, the glandular tissue is gradually replaced by connective tissue, resulting in a decrease in productivity.
The formation of milk is a complex physiological process in which not only the mammary gland, but also other organs and systems are involved. For the formation of milk, nutrients supplied to the udder with blood are used. In turn, nutrients enter the blood from digestive system. Therefore, for a highly productive cow, it is very important good development digestive organs.
For the formation of 1 liter of milk, 400-500 liters of blood must pass through the udder. Therefore, a cow must have a circulatory system capable of constant hard work.
Milk production is regulated by the nervous and hormonal systems. From the glands internal secretion The leading role is played by the pituitary gland, which releases hormones into the blood, in particular prolactin, which causes the secretion of milk.
Irritation of the nerve endings of the nipples during milking or sucking activates the pituitary gland, which enhances the secretion of milk.
The secretion of milk is carried out in the mammary gland. The epithelial cells lining the cavity of the alveoli synthesize the main components of milk: proteins, fats and milk sugar - lactose from the nutrients supplied with the blood. In the process of synthesis, they undergo significant changes. So, casein protein, except for milk, is not found anywhere in nature.
vitamins, mineral salts, hormones and enzymes enter the plasma from the animal's blood in finished form. However, in this case, the secretory cells do not play a passive, but an active role, working selectively. Therefore, the concentration of these substances in milk and blood is different. For example, in cow's milk, compared to blood plasma, there is 14 times more calcium, 9 times more potassium, 10 times more phosphorus, and 7 times less sodium.
However, of great importance for the formation of milk is the quantity and quality of "precursors", that is, substances from which the constituent parts of milk are formed.
In lactating cows, milk is continuously produced in the udder. First, milk fills the cavities of the alveoli, the excretory ducts, then the larger ducts, and lastly, the milk tanks. As milk accumulates in the udder due to a decrease in the tone of smooth muscles, the contractile strength of muscle fibers weakens. As a result, until a certain period, a significant increase in pressure in the udder does not occur and the conditions for the accumulation of milk remain. The filling of all udder cavities occurs within 10-12 hours, then the internal pressure begins to rise, the blood vessels are compressed, which leads to a gradual decrease in the secretory activity of the mammary gland. If the cow is not milked for 14-16 hours, then the pressure in the udder will increase so much that the secretion of milk will completely stop. If after that the cow is not milked, then the reverse process begins - the absorption of milk components.
Therefore, to maintain a high intensity of milk production, regular removal of milk from the udder is necessary. Skip milking, an excessively long interval between milkings inhibit milk formation and lead to a decrease in milk yield.
To prevent overflow of the udder with milk between milkings, it must be sufficiently capacious. It is possible to increase the capacity of the udder by appropriately preparing the heifers for calving.
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MILK GLANDS
MILK GLANDS
Udder - uber - the mammary gland of a cow. It is located in the caudal part of the ventral surface of the abdomen (Fig. 138). The udder, except for the nipples, is covered with hairy skin. The skin of the nipples lacks hair, sebaceous and sweat glands. The epidermis covering the skin of the nipples is thickened.
The streams of hair on the skin of the udder are directed from the abdominal wall to the udder lobes and caudally away from them. On the skin of the udder located between the thighs, a supra-pitched area is isolated - regio sup-ramammaria (milk mirror - planum lactiferum), bounded by lines meeting of two streams of short hairs: a stream of hair on the caudal surface of the udder, directed dorsally, and a stream of hair on the skin of the thigh area, directed ventromedially.
The skin of the udder before milking is smooth, after milking it forms vertical folds.
Under the skin is a superficial fascia in the form of a whitish thin strong plate of dense connective tissue. It covers the udder and passes dorsally into the superficial fascia of the abdominal wall. Under the superficial fascia lies the connective tissue membrane of the udder lobes. It is connected to layers of connective tissue within the udder lobes. Layers of connective tissue inside the udder lobes are called stroma - stroma glandula mamaria.
The udder is divided into right and left halves. Between them, along the median sagittal plane, there is a suspension ligament of the udder - ligamentum suspensorium uberis from elastic connective tissue. It is a continuation of the yellow (abdominal) fascia of the abdomen and an essential part of the suspension apparatus of the udder - the apparatus suspensorius mammarium, which attaches the udder to the wall of the abdomen. At the place of the ligament below the udder, the median groove of the udder is clearly marked - sulcus intermammarius. Each half of the udder consists of two main lobes: anterior and posterior. There may be additional underdeveloped lobes, more often ca-udal.
In the udder, a base is distinguished - basis uberis, located on the wall of the abdomen; body - corpus uberis; nipples - papilla. Most cows have an udder with four teats. Cows of a number of breeds have an udder with 6 nipples, for example, 30-40% of Simmental cows have 6 nipples, with four nipples and, accordingly, these lobes are well developed, and two nipples and their lobes are underdeveloped.
Rice. 138. Cow's udder
In the nipple, the base, body and tip are distinguished.
It is customary to distinguish between the udder of the following main forms (Fig. 139);
1) cup-shaped - the body of the udder is round, the height is significant, the nipples are widely spaced, the udder lobes are well developed and differ slightly from each other in size;
2) tub-shaped - the lobes are well developed, the body is of considerable height, elongated, the front edge of the udder is close to the center umbilical region, the length of the udder is 15-20% greater than the diameter of the udder;
3) flat - differs from the bowl-shaped lower body height;
4) goat - characterized by a cone-shaped body, nipples close in location, the height of the posterior lobes significantly exceeds the height of the small anterior lobes;
Rice. 139. Udder shape
5) "primitive" - small in size with small close nipples.
A good udder of high-milk cows, suitable for mechanical milking, has a tub-shaped or cup-shaped shape with cylindrical teats. The dimensions of such an udder are significant, for example, the circumference is 120-130 cm, the height is 25-30, the length of the nipples is 5-7, their diameter is 2-3 cm.
The glandular parts of the udder that produce milk. In the cells between the layers of whitish connective tissue (stroma) there are yellowish lobules of glandular tissue (parenchyma) of the mammary gland - lobuli glandule mammariae. Their size is 0.7-0.8 mm3. Through the layers of connective tissue, blood, lymphatic vessels, and nerve fibers pass and branch. In the lobules there are alveoli with a diameter of 50-350 microns and ducts (tubes).
In the walls of the alveoli (Fig. 140) and inside the lobular ducts there is a single-layer glandular epithelium that secretes milk, and myoepithelial cells, by contraction of which the alveoli and ducts are compressed, and the milk passes into the excretory lobular ducts.
Rice. 140. Milk alveoli and ducts
The system that removes milk consists of: a) milk ducts - ductus lactiferi of various diameters and structures; b) milk sinus - sinus lactiferi (milk tank). By location and structure, the following types of milk ducts are designated: intralobular; interlobular; milk ducts visible to the naked eye. In their walls there are smooth muscle fibers, milk ducts, formed from the fusion of the milk ducts. In the lactiferous sinus, the glandular part (above the nipple) is distinguished - pars glandularis, into which large milk ducts (passages) with a diameter of 5-15 mm open and the nipple part - pars papillaris, located inside the nipple. The inner part of the cistern is lined with a mucous membrane that forms longitudinal and oblique folds and papillae. On the border of the supra-nipple and nipple parts of the cistern there is a circular fold of the mucous membrane - plica anularis. The volume of the milk tank is larger in cows with high milk yields and smaller in low-dairy cows. The excretory system ends with the nipple duct (canal) - ductus (canalis) papillaris 5-15 mm long. The nipple duct is located at the tip of the nipple, and it distinguishes between the internal opening into which milk enters from the tank, and the external nipple opening - ostia papillaria. The inner opening is covered with folds of the mucous membrane. In the wall of the tip of the nipple there are smooth annular muscles that form the sphincter of the nipple around the nipple duct - shch. sphincter papilla.
Breast (glandula lactifera) depending on the type of animal or located on chest (glandula mamma), either located between the thighs in the groin area and is called the udder (?ber). The mammary glands are built according to the type of alveolar-tubular glands and consist of a glandular section, or parenchyma, and stroma, or a connective tissue skeleton. The udder does not belong to the system of reproductive organs, but is in close functional connection with them, complementing the complex function of reproduction.
At birth, the female has already formed nipples, interlobular septa and ligamentous apparatus, but adipose tissue is located in place of the future parenchyma. In heifers up to 6 months of age, the udder is a small cavity from which the system of ducts and milk passages departs. During this period, the udder grows at the expense of not glandular, but adipose and connective tissues.
With the onset of puberty, both the ducts and the alveolar apparatus begin to grow rapidly. The strongest growth and final development of the udder occurs during the first pregnancy. In the process of growth and development up to the beginning of the formation of milk, iron undergoes significant changes.
The mammary gland (udder) in cattle grows intensively and develops during the pregnancy of animals. During this period, the number of nerve fibers and blood vessels increases, and from the second half of pregnancy, the secretory epithelium begins to function, alveoli form (Fig. 6.1).
In a cow, the mammary gland (udder) is a glandular organ consisting of four quarters; each of them ends with a nipple below. Some cows, in addition to the main quarters, have two or even four additional lobes that do not contain parenchyma (polymastia).
The size and shape of the udder and teats depend on the breed, age, individual characteristics, lactation period, and the physiological state of the animals.
Milk quarters end in nipples (papillae uberis), which have a conical or cylindrical shape with a blunt or cone-shaped top. The apex without visible borders passes into the cylindrical part of the nipple, and the latter - into its base and without a sharp border - into the body of the mammary gland. The length of the nipples is usually from 2 to 15 cm.
Rice. 6.1
7 - artery and vein; 2 - nerve plexus; 3 - myoepithelium; 4 - branching of nerve fibers; 5 - a drop of milk fat; 6 - glandular epithelium; 7 - own shell of the alveoli; 8 - excretory duct; 9 - alveolar cavity
The wall of the nipple is covered on the outside with thin, elastic skin, devoid of hair, sweat and sebaceous glands. Under the skin at the nipple there is a layer of connective tissue of different thicknesses, which includes bundles of smooth muscle fibers running in different directions. At the apex, they form a relatively powerful circular muscle - the sphincter of the nipple canal. The mucous membrane lining the nipple part of the cistern, without a noticeable border, passes into the skin of the nipple. It is covered with a two-layered epithelium. The nipple part of the tank at the apex of the nipple passes into its canal.
The nipple canal is 0.5-1 cm long. Its mucous membrane is collected in oblong folds, closely adjacent to each other. The nipple canal itself is an opening, the walls of which are formed by connective tissue, a circular layer of muscles (the sphincter of the nipple canal) and a mucous membrane, which is collected in the smallest longitudinal folds. The nipple canal is always closed by its sphincter. The contraction of the radial fibers is a response to tactile stimulation of the nipple receptors or touch, and the contraction of the longitudinal fibers shortens or lengthens the nipple.
The udder is covered on the outside with soft, elastic skin, which forms a large number of folds, especially on the back surface. Due to the high elasticity of the mammary gland, it can significantly increase in volume when filling the container system with milk.
The skin of the udder is covered with delicate sparse hair, which grows from the bottom up and to the sides on the back surface of the udder, forming the so-called milky mirror. The shape and size of the milk mirror vary. The udder fits snugly against the ventral abdominal wall and is held in its position by the suspension ligament of the udder, superficial and deep fascia. The suspensory ligament divides the udder into right and left halves. From the deep fascia, trabeculae extend inward, which form a cellular framework for the delicate secretory tissue of the udder; blood and lymphatic vessels pass through it, reserve fat is also deposited in it (Fig. 6.2).
Components of the udder: glandular tissue, excretory ducts, interstitial connective tissue, blood, 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 ligament.
The udder parenchyma consists of alveoli ( alveolus) and excretory ducts. Each alveolus is the smallest functional part of the udder. Inside, it is lined with a single layer of secretory epithelium, which, depending on its functional state It can be cylindrical, cubic or flat. Outside, the alveolus is surrounded by myoepithelium, which has a stellate shape. When connected to each other, myoepithelial cells form a mesh around the alveoli, forming acini (Fig. 6.3). Myoepithelial cells are so named because they resemble the shape of the epithelium, but at the same time are able to contract like muscle elements. In addition to the alveoli, the myoepithelium envelops the milk ducts. Each alveolus has an outlet - a small milk duct. The ducts of many alveoli join together to form the middle lactiferous duct.
The middle ducts, heading down towards the nipple, merge and give rise to 12-50 wide excretory ducts - milk passages that flow into the cistern. The milk tank is the cavity of the nipple, sometimes extending upward into the parenchyma of the udder. It serves as a reservoir for milk.
The udder is very rich in blood vessels, arterial and venous capillaries form a dense network around each alveolus. The intensity of blood supply to the udder depends on its function.
mental state. The venous system of the udder is more developed than the arterial one. There are a large number of additional venous vessels, often anastomosing with each other and with the veins of the adjacent quarter.
Rice. 6.2.
a- lateral surface; b- segmental section; in- sagittal section; 7 - base; 2 - body; 3 - nipples; 4 - anterior lobes; 5 - posterior lobes; 6 - suspension ligament; 7 - superficial fascia; 8 - skin; 9 - lobules of glandular tissue; 10 - openings of milk passages (passages); 7 1 - supra-papillary glandular part of the milk tank; 12 - teat part of the milk tank; 13 - nipple canal (duct); 14 - connective tissue framework (stroma) of the lobe; 75 - lobules of glandular tissue (parenchyma)
Rice. 6.3.
- 7 - acini; 2 - milk move; 3 - intralobular duct; 4 - apocrine secretion; 5 - myoepithelial cells; 6 - nerve fiber; 7 - hemocapillary;
- 8 - lactocyte
According to the research of N.F. Bagdashov and A.P. Eliseev, the arterial vessels of the right and left halves of the udder form anastomoses between themselves. The number of anastomoses increases with age; heifers have almost none (A.I. Pospelov).
The milk vein goes from the udder to the milk well, then penetrates into abdominal cavity and falls into the inner thoracic vein(v. thoracica interna). The venous system is more developed than the arterial one. In addition to the veins of the same name with the arteries, there are many superficial and deep venous trunks, which have many twists and extensions, giving the udder a certain tuberosity.
The mammary gland has two venous plexuses: the plexus of the base of the nipple, which has a circular structure, and the nipple plexus, which has a longitudinally looped direction.
The circular venous plexus is located on the border of the cistern and the parenchyma; when overflowing with blood, it can close the lumen of the cistern.
The lymphatic system of the udder originates from the lymphatic clefts and spaces located around the alveoli, then collects the interlobular lymphatic vessels, passes through the lymph nodes into the lymphatic cistern, and then along the thoracic duct into the posterior vena cava.
Additionally, there is a rich lymphatic network of the skin of the udder. It begins in the skin of the base of the nipple, gives many anastomoses, and ultimately forms the lymphatic vessels of the udder quarter, the lymph from which enters the lymphatic system pelvic cavity, and partly in the lymph nodes of the inguinal region.
The innervation of the udder is carried out by branches and 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 gland lobules.
Three pairs of somatic nerves are involved in the innervation of the mammary gland: external spermatic (n. spermaticus externus), ilioinguinal (n. ilioinguinalis), ilioceliac (n. iliohypo-gastricus) and partly the perineal nerves. The main role in the innervation of the parenchyma of the udder is played by the external seminal nerve; the remaining cerebrospinal nerves innervate mainly the skin. In addition to the somatic nerves, the mammary gland is served by a rich network autonomic nerves, extending from the nerve plexuses of the blood vessels of the udder. Efferent sympathetic innervation is carried out by branches extending from the 2nd-4th lumbar nodes of the border column and from the sacral nodes. These fibers enter the udder as part of the external seminal, iliohypogastric, and ilioinguinal nerves.
Distinctly distinguishable nerve trunks accompany the vessels of the cistern and milk ducts to the cistern and nipple, where they end in the skin of the nipple and the mucous membrane of the cistern. Irritation of receptors located in the thickness of the udder tissues affects the blood circulation, respiration, digestion and reproductive system of the animal.
Breast growth is controlled by hormones from the ovaries, adenohypophysis, and adrenal glands.
Anderson in 1974 proposed the following scheme of hormonal induction of mammary gland development and lactogenesis (GH - growth hormone; P - progesterone; Pr - prolactin).
Animal mammary gland I Estrogens + GH + corticosteroids
duct growth
I Estrogens + P + Pr + GH + corticosteroids Lobuloalveolar tissue growth I Pr + corticosteroids Milk secretion
Consequently, ovarian hormones play an important role in the development of the mammary glands (Fig. 6.4). Estrogenic hormones of the ovaries, as well as synthetic estrogens, accelerate the growth of the ducts of the gland, the development of the alveoli and milk lobules. Hormone corpus luteum- progesterone - accelerates the growth of the ducts, and progesterone, together with estrogens, is necessary for the development of the lobular-alveolar structure. The effect of estrogens and progesterone on the development of the mammary glands is weak with the pituitary gland removed, which means that sex steroids affect the mammary glands in two ways: by stimulating the release of adenohypophysis hormones (somatotropic, adenocorticotropic and prolactin) and acting directly on the gland tissue (in the presence of adenohypophysis hormones ).
The secretory process is carried out directly in the epithelial cells of the alveoli and small ducts, with each epithelial cell producing all the components of milk. The resulting product is released into the cavity of the alveoli, accumulates in them, passing in the process of milking into the ducts and the milk tank. The overflow of the alveoli with milk inhibits secretion, the periodic emptying of the glands stimulates it.
Thus, lactation is carried out by the secretory activity of the alveolar apparatus and cells lining the milk ducts of the mammary gland (milk formation), and milk flow occurs as a result of contraction of the myoepithelium of the alveoli and milk ducts, the muscular elements of the milk passages into the cisterns. Milk production is promoted by erection of the udder.
Rice. 6.4.
Udder erectile refers to the process of overflow of the udder with blood, which is observed during milking or sucking. Due to the overflow of the mammary gland with blood, increased pressure is created in the interalveolar spaces, which leads to their compression.
The process of milk formation is not just blood filtration, but a complex secretory process, as a result of which nutrients from the gastrointestinal tract into the blood are secreted into milk components necessary for the life of the fetus.
In the process of mammogenesis, the following stages are distinguished:
- sorption of milk precursors from the blood;
- synthesis of milk constituents in the secretory cells of the mammary gland;
- formation, accumulation and movement of synthesized products in the cytoplasm of secretory cells;
- secretion of milk by secretory cells into the cavity of the alveoli. Milk contains proteins (casein, albumins, globulins), fats,
milk sugar - lactose, macro- and microelements and all groups of vitamins. The synthesis of fats, proteins, milk sugar and other components of milk occurs in the mitochondria of the alveolar epithelium. The synthesis of casein and lactose increases sharply immediately before and after childbirth, which is apparently due to a decrease in the blood plasma level of progesterone during this period, the most likely inhibitor of lactogenesis.
The milk ejection reflex is carried out as a result of the interaction of the nervous, endocrine and vascular systems. When the mammary gland is stimulated along the afferent nerves, afferent impulses are transmitted to the afferent neurons of the spinal nodes and dorsal columns. gray matter the spinal cord, from here, through the intercalary neurons of the gray matter, the signal enters the efferent neurons of the ventral columns of the gray matter and is transmitted along the motor axons to the mammary gland. It's short reflex arc, built by analogy with motor reflexes, it provides a decrease in the tone of the smooth muscles of the udder and the opening of the sphincters of the ducts and nipples. As a result, an allowance occurs and the cistern portion of milk is easily removed.
Milking has a positive effect on blood circulation in the udder. Machine milking preceded by a 10 second teat hygiene treatment causes a significant increase in blood flow through the udder. The maximum blood flow is on average 154.4% of the volumetric blood flow velocity. The stimulating effect of machine milking on blood circulation in the udder is explained by the vasodilating effect of oxytocin released from the neurohypophysis as a result of the milk ejection reflex.
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