The external characteristic of the udder of a cow
Normally, four quarters occur in cows, less often only two develop, or additional ones appear without developed glandular tissue and with disorders.The skin is covered with delicate hairs that form a milky mirror on the hindquarters - growth from the bottom up and to the sides. The shape and size of the milk mirror largely determines productivity.
The mammary gland is tightly attached to the ventral abdominal wall, where it is held by a suspensory ligament.
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Functions and morphology of the mammary gland
The structural unit of the udder is a quarter, each of which consists of:- glandular tissue;
- connective tissue;
- excretory ducts;
- vessels;
- nerve fibers.
- milk formation;
- milk yield.
- progesterone;
- somatotropin;
- prolactin;
- adrenocorticotropin;
- oxytocin;
- adrenaline and others.
Also the process lactation located in relationships with returns- if the cow is not milked, the production of milk will decrease, and over time it may completely stop. This property is based on the natural method running cows without the use of special tools.
Lactation occurs a few days before childbirth, or immediately after them. During the first days, the alveoli produce colostrum - a specific substance, rich in nutrients and antibodies, thick in texture and salty in taste.
After 7-10 days, regular milk begins to form in the milk alveoli, the glandular tissue continues to actively develop for the next 4-6 months with an increase in milk production.
Anatomy of the mammary gland in cows
The structural unit of the udder is a quarter, each of which consists of a number of tissues and formations. The key link here is the alveolar glandular tissue, in which milk and colostrum are formed. The alveoli with the outgoing duct are braided with stellate cells that can contract. They squeeze the secret from the alveoli into the ducts.Alveolar ducts are further combined into middle ones, which, together with the surrounding parenchyma, form udder segments. Merging, the middle ducts form milk passages that flow into the cistern.
blood supply The udder is carried out by the following arteries and veins:
- perineal arteries;
- external pudendal artery and vein;
- vein and artery of the milk tank;
- subcutaneous abdominal milk vein.
Nervous system represented by branches of the nerves of the abdominal organs - nervus iliohypogastricus, n. ilioinquanalis.
Structure of a cow's udder
- Go to the section heading: Structure (anatomy, morphology) and physiology of the cow
The mammary gland of a cow is her udder. The udder of a cow consists of four lobes: two anterior and two posterior, and each of them has its own nipple. Due to the fact that the udder lobes do not communicate with each other, milk from one lobe cannot get into others, which is especially important when local diseases occur - for example, mastitis in one of the lobes. Two halves of the udder: left and right, are separated from each other by an elastic partition, which not only divides the mammary gland into two parts, but also supports it. Over time, its elasticity weakens, and therefore, in older cows, the udder becomes more pendulous.
An analysis of the anatomy of the udder shows that the udder consists of various tissues: glandular, fatty and connective, each of which performs its own functions. In the glandular tissue, which consists of a large number of tiny vesicles - alveoli, milk is formed. Milk is produced in special cells that line the inner surface of the alveoli. From the alveoli, the accumulated milk first enters the smallest milk ducts, which are connected to larger milk ducts, and they become larger as they merge, forming the milk ducts. As a result, milk flows through even wider milk ducts into four milk tanks, and each tank ends with a nipple section.
Inside the nipple there is an excretory canal, at the end of which there is a sphincter, which is a circular muscle that prevents milk from spontaneously flowing out. When milking, the sphincter relaxes, which allows milking out of the milk in the udder. Calculations show that by the time the cow is milked, the tanks contain up to 25% of the milk accumulated in the udder, while the remaining 75% is still in the ducts and alveoli. Therefore, if a catheter in the form of a hollow tube is inserted into the teat of the udder, then only milk from the tank will spontaneously flow out, and the rest will remain in the udder, which can only be removed by milking.
Connective tissue is located around the glandular tissue in the udder, which mainly performs two functions: supporting and protective, protecting the udder from adverse effects. external environment. The tissues of the udder are equipped with many sensitive nerve endings that transmit various stimuli to the central nervous system.
Outside, the udder is covered with elastic skin with sparse and delicate short hairs. In high-yielding cows, the udder skin is thinner and more elastic. With adverse environmental influences, as well as poor care, dampness and drafts in the room, the rapid movement of cows, the skin on the udder is easily damaged, which can be one of the causes of the disease of the udder - mastitis. On this basis, one can judge the productive qualities of a cow can be judged by the skin of the udder - the thinner and more elastic it is, the more milk this cow can give.
By the end of milking, the udder decreases in volume and falls off. And then on it, especially on its back side, many folds form, which are called the udder reserve, and by their severity one can judge the capacity and productivity of the mammary gland. 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 udder of a cow is an organ in which milk is produced from the blood of an animal.
The udder (Fig. 1) consists of two halves: right and left. Each half is divided into anterior and posterior lobes. Thus, the udder has four independent lobes, often unevenly developed: in most cows, more milk is produced in the hind lobes than in the front. Milk cannot pass from one lobe to another. The composition of each lobe includes: mammary gland, connective tissue, milk leaks and nipple. The glandular tissue, which is the most important part mammary gland is made up of huge amount very small sacs - alveoli. From the inside, the alveoli are lined with a single-layer secretory epithelium that produces milk. Through the tubules, covered from the inside with the same epithelium, they communicate with the milk ducts, which flow into the milk tank, which, in turn, communicates with the nipple.
On fig. 2 shows a section of one quarter of the udder and a diagram of the alveoli.
The surface of the alveoli, which hold 1 liter of milk produced by them before milking, can be determined by simple calculations. The average diameter of the alveolus can be taken equal to 0.2 mm. The working volume of one alveolus, having a diameter of 0.0002 m, will be
The number of alveoli required to accommodate 1 liter of milk is determined by the following expression:
The working surface of one alveolus is
The total surface area of all alveoli that contain 1 liter of milk
Since before milking, the alveoli of a dairy cow of average productivity contain several liters of milk, the working surface of the alveoli of the entire udder is more than 100 m2. Such a huge working surface of the udder alveoli of an animal makes us think about the complexity and perfection of its control system. A huge number of alveoli, working in parallel, could not act equally effectively without such perfect control. It should be taken into account that the entire alveolar system also undergoes significant changes during each lactation. Probably, the complexity of this system can explain its great sensitivity to external influences, which manifests itself in the disease of cows. mastitis, as well as fluctuations in the productivity and composition of milk.
Therefore, engineers and designers involved in the design of milking machines should not ignore the biological issues affecting the morphology and physiology of the lactating organs of animals.
The udder of a highly productive cow can accumulate up to 25 liters of milk. A significant part of it (up to 50%) is in the alveoli before milking, and the rest fills the ducts and cisterns of the udder and teats.
The removal of milk from the alveoli does not occur by gravity, but with the help of myoepithelium, i.e., star-shaped muscle cells surrounding the alveoli and capable of contracting. By contracting, these cells squeeze milk from the alveoli into the milk ducts, from where it enters the milk tank and then into the nipple.
The retention of milk in the udder, in addition to the obturator sphincter at the end of the nipple, is facilitated by the special arrangement of the ducts and canals, which have many constrictions and expansions. In addition to a dense network of blood vessels, the udder has a well-developed system of lymphatic vessels and nerve fibers. The largest number of nerve endings (receptors) is located in the nipples. Outside, the udder is covered with soft and very elastic skin with sparse hair; there is no hair on the nipples.
Teats in cows vary in both size and shape. At the end of the nipple there is a muscular sphincter, which, when externally applied to the nipple, unclenches during milking. The stiffness of the cow depends on the state of this muscle.
It has now been established that during sucking or milking, irritation from the nerve endings of the nipples enters the central nervous system (brain) of the animal, from where a command is sent to the pituitary gland. The latter releases hormones (mainly oxytocin) into the blood, which cause contraction of the udder myoepithelium, as a result of which milk passes from the alveoli into the milk ducts and further into the cistern and nipples.
Cow's milk contains on average 87.5% water, 3.8% fat, 3.3% protein, 4.7% milk sugar and 0.7% minerals. However, its composition is different for different cows, and for the same cow it varies depending on feeding, maintenance, lactation time, etc. The amount of fat in milk is less in the first months after calving and more before starting a cow. During the day, the percentage of fat in milk also does not remain constant.
Previously, it was believed that a significant part of the milk is formed in the udder during milking. This was explained by the fact that the udder, allegedly, cannot accommodate all the milk that is given out of it in one milking. This claim was subsequently refuted. Milk is produced in the udder between milkings during the so-called period of free lactation, and only a small part of it is produced during milking. As milk accumulates in them, the alveoli of the mammary gland gradually stretch, and when the udder is about 80-90% full, they are very stretched. With further accumulation of milk, the pressure in the udder increases markedly, the formation of milk slows down and soon stops altogether. As milk is removed from the udder, the pressure in it decreases.
Usually milking is carried out 3-4 times a day. If a cow does not give milk in one of the milkings, it can be milked less often without compromising productivity. So, some farms switched to two-time milking of cows, which significantly improved the conditions for the use of machine milking: with two-time milking, cows are milked faster and cleaner, and reducing the number of milkings is in some cases economically beneficial. Abroad, double milking is generally accepted.
It should be noted that the issues of the structure of the udder, secretion and return of milk are still little studied. There is especially a lot of uncertainty in the study of the rate of milking and the influence of one or another type of milking on the productivity of cows. This is explained by the fact that the processes occurring in the udder are complex and it is often impossible to study them by direct methods.
The milk ejection reflex has a two-phase character: the contraction of the myoepithelium and the squeezing of milk from the alveoli is preceded by a short-term decrease in the tone of the muscles of the cisterns and a slight drop in pressure in the udder. Then the tone of the smooth muscles of the cisterns and wide ducts increases, and the milk, after the forced opening of the sphincter of the nipples, comes out. The rise and fall of udder pressure is repeated as milk is produced. This process facilitates the placement in tanks and ducts of milk flowing out of the alveoli during milking. Periodic emptying of the mammary gland stimulates the production of milk in the udder of the cow.
The cow's udder is very well developed. It was formed by the merger of 2 (3) pairs of glands. The right and left half of the udder with 2, less often with 3 teats, are separated from each other by a sagittal groove. The anterior and posterior lobes of each half of the udder are fused without clear boundaries, but there are 2 (3) systems of milk passages in the parenchyma, each with its own teats. The milk ducts open into the milk cistern. The latter descends to the base of the nipple and is divided by an annular fold into two sections - basal, or glandular, and nipple. The udder of high-milk cows has a tub-like or cup-like shape with cylindrical teats. The nipples reach a length of 6-9 cm, most of all they have an approximately cylindrical shape and one opening of the nipple canal.
The skin of the udder
The udder is covered with relatively delicate skin with thin hairs. There are no hair, sebaceous and sweat glands in the skin of the nipples. The epidermis covering the skin of the nipples is thickened, elastic, durable, and can withstand the sucking movements of the lips and tongue of the calf, squeezing the nipples with fingers and the walls of milking cups.
During the dry period (cessation of lactation before calving), the volume of the udder decreases. A significant part of the alveolar cuttings and ducts is destroyed by leukocytes. The thickness of the stroma layers increases by 2-3 times.
Before calving, there is a significant expansion of the blood vessels of the udder, the epithelium of the alveoli in the lobules is restored, the udder increases in volume; the secretion of colostrum begins.
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 a useful nutritious product that is 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 different breeds 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 time period 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 appearance mammary gland an experienced animal husbandry specialist can determine whether a cow has a high milk yield or belongs to meat direction with low milk production.
Location and structure of the udder
The mammary glands of a cow are called the udder. The udder is divided into four mammary glands, forming the right and left parts. 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. Their insides are 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 various irritations to the central nervous system. 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 start such a complex process as milk production 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 the adverse effects of the 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 the 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. Of the endocrine glands, the pituitary gland plays a leading role, 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 supraglottic region is distinguished - regio sup-ramammaria (milk mirror - planum lactiferum), limited by the lines of meeting of two streams of short hair: a stream of hair on the caudal surface of the udder, directed dorsally, and a stream of hair on the skin of the thigh, 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 teats, for example, 30-40% of cows Simmental breed 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) bath-shaped - the lobes are well developed, the body is of considerable height, elongated, the front edge of the udder is close to the center of the 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 they designate the following types milk ducts: 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.
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