01 Primary Production of Milk

8/12/2019 01 Primary Production of Milk

1/16

Dairy Processing Handbook/Chapter 1 1

Milk production began 6 000 years ago, or even earlier. The dairy animalsof today have been developed from untamed animals which, over

thousands of years, have lived at different altitudes and latitudes, attimes exposed to natural and, many times, severe and extreme

conditions.

Practically everywhere on earth man started domesticating animals. As arule, herbivorous, multipurpose animals were chosen to satisfy his need ofmilk, meat, clothing, etc.

Herbivorous animals were chosen because they are less dangerous andeasier to handle than carnivorous animals. The former did not competedirectly with man for nourishment, since they ate plants which man couldnot use himself.

Primary production of milk


2/16

Dairy Processing Handbook/Chapter 12

The herbivorous animals used were all ruminants with the exception ofthe mare and ass. Ruminants can eat quickly and in great quantities, andlater ruminate the feed. Today, the same animals are still kept for milkproduction, milk being one of the essential food components for man.

The most widespread milking animal in the world is the cow, which isfound on all continents and in nearly all countries.

Table 1.1

Composition of milk from various animals.

Animal Protein Casein Whey Fat Carbo- Ashtotal protein hydrate

% % % % % %

Human 1,0 0,5 0,5 4,5 7,0 0,2Horse 2,2 1,3 0,9 1,7 6,2 0,5Cow 3,5 2,8 0,7 3,7 4,8 0,7Buffalo 4,0 3,5 0,5 7,5 4,8 0,7Goat 3,6 2,7 0,9 4,1 4,7 0,8Sheep 4,6 3,9 0,7 7,2 4,8 0,8

However, we should not forget the other milking animals, whose milk isof great importance to the local population, as a source of highly valuableanimal protein and other constituents. Sheep are of exceptional importanceamong this group, especially in the Mediterranean countries and in largeareas of Africa and Asia. The number of sheep in the world exceeds onebillion, and they are thus the most numerous of all milk- and meat-producing domestic animals.

Sheep are often accompanied by goats, whose contribution to milk and

meat production in the poorest areas should not be overlooked. Both sheepand goats are a source of cheap, high-quality protein and are mainly kept inconditions where climatic, topographical, economic, technical orsociological factors limit the development of more sophisticated proteinproduction systems.

Table 1.1 shows the composition of milk from different species ofanimals. It should be noted that the figures given are only averages, as thecomposition for any species is influenced by a number of factors such asbreed, feeding, climate, etc.

Cow milkMilk is the only food of the young mammal during the first period of its life.The substances in milk provide both energy and the building materialsnecessary for growth. Milk also contains antibodies which protect the youngmammal against infection. A calf needs about 1 000 litres of milk for growth,and that is the quantity which the primitive cow produces for each calf.

There has been an enormous change since man took the cow into hisservice. Selective breeding has resulted in dairy cows which yield anaverage of more than 6 000 litres of milk per calf,i.e.six times as much asthe primitive cow. Some cows can yield 14 000 litres or more.

Before a cow can start to produce milk, she must first have a calf.Heifers reach sexual maturity at the age of seven or eight months but arenot usually mated until they are 15 18 months old. The period of gestation

is 265 300 days, varying according to the breed of the cow, so a heiferproduces her first calf at the age of about 2 2,5 years.

The heifer is bred (naturally orby insemination) before theage of two years.

The gestation period is ninemonths and one week.

After calving, the cow givesmilk for 10 months.

1 2 months after calving thecow will again be bred.


3/16


Secretion of milkMilk is secreted in the cows udder, which is a hemispherical organ dividedinto right and left halves by a crease. Each half is divided into quarters by ashallower transverse crease. Because each quarter has one teat with itsown separate mammary gland, it is theoretically possible to get milk of fourdifferent qualities from the same cow. A sectional view of the udder isshown in Figure 1.1.

The udder is composed of glandular tissue which contains milk-producing cells. The external layer of this tissue is muscular, thus givingcohesion to the body of the udder and protecting it against injury fromknocks and blows.

The glandular tissue contains a very large number (about two billion) oftiny bladders called alveoli. The actual milk-producing cells are located onthe inner walls of the alveoli, which occur in groups of between 8 and 120.Capillaries leading from the alveoli converge into progressively larger milkducts which lead to a cavity above the teat. This cavity, known as thecistern of the udder, can hold up to 30 % of the total milk in the udder.

1

3

4

2

Large quantities of blood flowthrough the udder every day.Approx. 800 900 l of blood isneeded for formation of one litreof milk.

Fig. 1.1Sectional view of the udder.

1 Cistern of the udder2 Teat cistern3 Teat channel

4 Alveolus

The cistern of the udder has an extension reaching down into the teat; thisis called the teat cistern. At the end of the teat there is a channel 1 1,5 cmlong. Between milkings, the channel is closed by a sphincter muscle whichprevents milk from leaking out, and bacteria from entering the udder.

The whole udder is laced with blood and lymph vessels. These bringnutrient-rich blood from the heart to the udder, where it is distributed bycapillaries surrounding the alveoli. In this way, the milk-producing cells arefurnished with the necessary nutrients for the secretion of milk. Spentblood is carried away by the capillaries to veins and returned to the heart.The flow of blood through the udder very high. It takes between 800 and900 litres of blood to make one litre of milk.

As the alveoli secrete milk, their internal pressure rises. If the cow is notmilked, secretion of milk stops when the pressure reaches a certain limit.Increase of pressure forces a small quantity of milk out into the larger ductsand down into the cistern. Most of the milk in the udder, however, iscontained in the alveoli and the fine capillaries in the alveolar area. Thesecapillaries are so fine that milk cannot flow through them of its own accord.

It must be pressed out of the alveoli and through the capillaries into thelarger ducts. Muscle-like cells surrounding each alveolus perform this dutyduring milking, see Figure 1.2.

Fig. 1.2Squeezing of milk from

alveolus.

In the Irish village of Blackwater,Big Bertha died on 31 December1993. She was probably theoldest cow in the world when shedied at an age of 49 years. Theowner, Mr Jerome OLeary,announced that Big Berthawould have been 50 years of ageon 15 March 1994.


4/16


77

88

55

44

3399

1111

1010

121211

22

66llllll

l

l

l

l

l

l

l

l

l

l

l

l

l

l

l

l

ll

l l l l l

ll

l

l

l

l

l

l

l

l

l

l

l

l

l

l

l

l

ll

ll

Fig. 1.3 Milking takes 5 8 minutes.

Fig. 1.4The milk should be pouredthrough a strainer and then chilled.

The lactation cycleSecretion of milk in the cows udder begins shortly before calving, so thatthe calf can begin to feed almost immediately after birth. The cow thencontinues to give milk for about 300 days. This period is known as lactation.

One to two months after calving the cow can be serviced again. Duringthe lactation period, milk production decreases, and after approx. 300 daysit may have dropped to only 25 50 % of its peak volume. At this stage

milking is discontinued to give the cow a non-lactating period of up to 60days prior to calving again. With the birth of the calf, a new lactation cyclebegins. The first milk the cow produces after calving is called colostrum. Itdiffers greatly from normal milk in composition and properties. See further inChapter 2.

Milk production is somewhat lower during the first lactation period. Acow is normally productive for 3 5 years.

MilkingA hormone called oxytocin must be released into the cows bloodstream inorder to start the emptying of the udder. This hormone is secreted and

stored in the pituitary gland. When the cow is prepared for milking by thecorrect stimuli, a signal is sent to the gland, which then releases its store ofoxytocin into the bloodstream.

In the primitive cow, the stimulus is provided by the calfs attempts tosuck on the teat. The oxytocin is released when the cow feels the calfsucking. A modern dairy cow has normally no calf present during milking.Stimulation of the milk let-down is done by the preparation of milking,i.e.the sounds, smells and sensations associated with milking.

The oxytocin begins to take effect about one minute after preparationhas begun and causes the muscle-like cells to compress the alveoli. Thisgenerates pressure in the udder and can be felt with the hand; it is knownas the let-down reflex. The pressure forces the milk down into the teatcistern, from which it is sucked into the teat cup of a milking machine or

pressed out by the fingers during hand milking.The effect of the let-down reflex gradually fades away as the oxytocin is

diluted and decomposed in the bloodstream, disappearing after 5 8minutes. Milking should therefore be completed within this period of time. Ifthe milking procedure is prolonged in an attempt to strip the cow, thisplaces an unnecessary strain upon the udder; the cow becomes irritatedand may become difficult to milk.

Hand-milkingOn many farms all around the world, milking is still done by hand in thesame way as it has been done for thousands of years. Cows are usuallymilked by the same people every day, and are quickly stimulated to let-down just by hearing the familiar sounds of the preparations for milking.

Milking begins when the cow responds with the let-down reflex. The firstjets of milk from the teats are normally rejected. A careful, visual inspectionof the first milk enables the milker to detect the status of the udder health.

Two opposed quarters are milked at a time: one hand presses the milkout of the teat cistern, after which the pressure is relaxed to allow more milkto run down into the teat cistern from the udder cistern. At the same timemilk is pressed out of the other teat. In this way the two teats are milkedalternately. When two quarters have been emptied in this way, the milkerthen proceeds to milk the other two until the whole udder is empty.

The milk is collected in pails and poured through a strainer, to removecoarse impurities, into a churn holding 30 50 litres. The churns are thenchilled and stored at low temperature to await transport to the dairy.Immersion or spray chillers are commonly used for cooling.


5/16


Machine milkingThe basic principle of the milking machine is shown in Figure 1.6. Themilking machine extracts the milk from the teat by vacuum. A vacuumpump, a vacuum vessel, a vessel for collecting milk, teat cups and apulsator are essential parts of the milking machine.

The teat cup unit consists of a teat cup containing an inner tube of

rubber, called the teat cup liner. The inside of the liner, in contact with theteat, is subjected to a constant vacuum of about 50 kPa (50% vacuum)during milking.

The pressure in the pulsation chamber (between the liner and teat cup) isregularly alternated by the pulsator between 50 kPa during the suctionphase and atmospheric pressure during the massage phase. The result isthat milk is sucked from the teat cistern during the suction phase. Duringthe massage phase, the teat cup liner is pressed together allowing a periodof teat massage. This is followed by another suction phase, and so on, asshown in Figure 1.7.

Relief of the teat during the massage phase is necessary to avoidaccumulation of blood and fluid in the teat. Such congestion in the teat canbe painful to the cow, and milk let down and milking performance can beaffected. Repeated congestion at successive milking sessions can evenhave an influence on the udder health. The pulsator alternates betweensuction and massage phases about 50 to 60 times per minute.

The four teat cups, attached to a manifold called the milk claw, are heldon the cows teats by suction and the friction between the teat and the teatcup liner. Vacuum is alternately (alternate pulsation) applied to the left andright teats or, in some instances, to the front teats and rear teats. Theapplying of vacuum to all four teats at the same time (simultaneouspulsation) is less common. The milk is drawn from the teats directly to themilk pail or via a vacuumised transport pipe to a receiver unit. An automatic

Fig. 1.6Machine milking equipment.

+

+

+

+

+

+

+

a

a

Fig. 1.7The phases of machine milking.

a Teat cup liner

Fig. 1.5Preparing the cow for milking by cleaning and massaging the udders beforethe teat cups are placed on the udders.

Fig. 1.8General design of pipeline milking system.

1

2

3

4

1 Vacuum pump2 Vacuum pipeline

3 Milk cooling tank4 Milk pipeline


6/16


shut-off valve operates to prevent dirt from being drawn into the system if ateat cup should fall off during milking. After the cow has been milked, themilk pail is taken to a milk room where it is emptied into a churn or a specialmilk tank for cooling.

To eliminate the heavy and time-consuming work of carrying filled pails tothe milk room, a pipeline system may be installed for direct transport of themilk to the milk room (Figure 1.8). Such systems are most common today. Itallow milk to be conveyed in a closed system straight from the cow to acollecting tank in the milk room. This is a great advantage from a hygienicpoint of view.

Regardless if the milking system is of bucket, pipeline or automatic typeit is important that it is designed to prevent air leakage during milking.Excessive air leakage can influence the quality of the milk and causeelevated levels of free fatty acids.

The machine milking plant is also provided with Cleaning-In-Place (CIP)facilities.

Automatic milking systemsAutomatic milking systems, Figure 1.9, have been installed on commercialfarms at an increasing rate in recent years. The potential benefits are

reduced labour requirements, higher milk quality, improved animal healthand increased yield. Figure 1.11 shows a typically dairy farm layoutincluding an automatic milking system.

Fig. 1.9The heart of an automatic milking system.The cow goes when she wants into the milking

station where the teats are cleaned and milked.

Fig. 1.10Teat-cup for cleaning, drying

and pre-milking. The teat is flushed withtepid water for cleaning and finally dried

with air. The pre-milk goes together withcleaning water to drain.

In contrast to conventional milking, in which people bring the cows to bemilked, automatic milking places emphasis on the cows inclination to bemilked in a self-service manner several times a day. The idea that cows likebeing milked is very attractive, and one of the main financial benefits fromautomatic milking is the increase in milk yield from more frequent milking.

When the cow wants to be milked, she walks to the milking station. Atransponder on the cow identifies it, and if the cow was milked recently, sheis directed back to the resting or feeding area.

The cow enters the automatic milking station and an individual amount ofconcentrate is served.


7/16


In an automatic milking system the teats can be detected by a laser andvision camera. As an example, the teats can be cleaned separately bymeans of a teat-cup-like device, Figure 1.10, using tepid water appliedintermittently at a certain pressure and turbulence to ensure efficientcleaning. Drying of the teats is carried out by compressed air in the sameteat-cup.

Foremilking is carried out by the cleaning teat-cup, which appliesvacuum at the end of the cleaning cycle. The cleaning teat-cups are finallyflushed with water.

Sensors can detect whether foremilking has been carried out.Foremilking is applied for a few seconds to ensure that sufficient milk isevacuated and the let-down reflex is activated.

The teat-cups for milking are automatically attached sequentially. Milkfrom the four teats is kept separate until the milk meter records the amountfrom each quarter. Spraying each individual teat with disinfectant is the finalstage of milking.

Milk yield, milking duration, milk flow rate, and certain characteristics ofthe milk are recorded during milking. In addition, data on cow movements,time of milking and time of concentrate feeding may also be available.

Milk leaving the milking station can be divided into different categoriesand being collected separately from the normal milk. The categories can be:1 Treated cow

2 Freshly calved cow (colostrum)3 Cow with less than one milking in the last 24 hours4 A cow which, although healthy, has cell counts above a certain levelThe fresh milk is forwarded to a buffer tank for cooling before beingpumped to the storage tank.

Cooling of milkEfficient cooling of the raw milk after milking is the best way to preventbacterial growth. Various cooling systems are available; the choice dependson the produced volume of milk.

Anin-cancooler, shown in Figure 1.13, is suitable for small producers. Itis much favoured by users of chilled water units and producers using direct-to-can milking equipment.

Animmersion cooler is designed for direct cooling of the milk in churns

7

5

6

4

3

2

1

Fig. 1.11Layout of a modern dairy farm with an automatic milking system.

1 Automatic milking station2 Control room3 Milk cooling and storage

4 Smart gate for preselecting the cowsattempting the milking station

5 Living area6 Feeding station

7 Calf section

Fig. 1.12Milk must be cooled to 4 C assoon as possible.

0 0

10


8/16


as well as in tanks. The condensing unit is mounted on a wall, Figure 1.14.The evaporator is located at the lower end of the immersion unit.The immersion cooler can also be used for indirect cooling,i.e.for

cooling water in insulated basins. The milk is then cooled in transportchurns immersed in the chilled water.Insulated farm tanks for immersion coolers are available in both

stationary and mobile types (Figure 1.15). When road conditions preventaccess by tanker truck, a mobile tank can be used to bring the milk to asuitable collection point. Mobile tanks are easy to transport and thussuitable for milking in the fields.

Direct expansiontanks as shown in Figure 1.16 can as well be used forcooling and storage of the milk.

Cleaning and sanitisingManual cleaningwith brushes is a common method where hand milking orbucket machine milking systems are used.

Circulation cleaningis commonly performed in pipe line milking plants.The cleaning solution is circulated through the plant by vacuum and/or apump.

Detergents, sanitisers, liquid temperatures and other cleaning conditionsrecommended by the milking machine supplier should be applied.

Cooling of milk on the farmMilk leaves the udder at a temperature of about 37 C. Fresh milk from ahealthy cow is practically free from bacteria. It must be protected from

1

Fig. 1.17Milking equipment on a large farm with heat exchanger (1) for rapid cooling from 37 to 4 C.

Fig. 1.16Direct expansion tank used for

cooling and storage of milk.

Fig. 1.14 The immersion cooler is placed

directly on the transportation churn.

Fig. 1.15 Theinsulated farm

tank can be filled

in the field andeasily transported

to the chilling unit.

Fig. 1.13An in-can cooler is placed on

top of the milking bucket or any type ofmilk can.


9/16


being contaminated after it has left the udder. Micro-organisms capable ofspoiling the milk are everywhere on the udder, on the milkers hands, onairborne dust particles and water droplets, on straw and chaff, on the cowshair and in the soil. It is common to filter the milk before it enters the milktank.

Careful attention must be paid to hygiene in order to produce milk ofhigh bacteriological quality. However, despite all precautions, it isalmost impossible to completely exclude bacteria from milk. Milk is anexcellent growth medium for bacteria; it contains all the nutrients theyneed. Thus, as soon as bacteria get into milk, they start to multiply. Onthe other hand, the milk leaving the teats contains certain originalbactericides which protect the milk against the action of micro-organisms during an initial period after extraction. It also takes sometime for infecting micro-organisms to adapt to the new medium beforethey can begin to grow.

Unless the milk is quickly cooled down after extraction, it may soonbe spoiled by micro-organisms, which thrive and multiply most vigorously attemperatures around 37 C. Milk should therefore be cooled immediatelyafter it leaves the cow. At this temperature the level of activity of the micro-organisms is low. It is important to keep the milk at low temperature during

storage. The activity of the micro-organisms will easily increase again if thetemperature is allowed to rise some few degrees above recommendedstorage temperature. Figure 1.18 shows the rate of bacterial growth atdifferent temperatures over time.

Under certain circumstances, e.g.with limited availability of water and/orelectricity or when the quantity of milk is too small to justify the investmentin cooling equipment on the farm, co-operative milk collecting centres withcooling facilities may be available.

Farm cooling equipmentSpray or immersion coolers are commonly used on farms, which delivermilk to the dairy in cans. In the spray cooler, circulating chilled water issprayed on the outsides of the cans to keep the milk cool. The immersion

cooler consists of a coil, which is lowered into the can. Chilled water iscirculated through the coil to keep the milk at the required temperature(Figure 1.13 to 1.15).

Where milking machines are used, the milk is commonly collected inspecial milk tanks at the farm (Figure 1.16). A wide range of milk tanks ofvarious sizes are available with built-in cooling equipment designed toguarantee cooling to a specified temperature within a specified time. Thesetanks are often in most cases equipped with equipment for automaticcleaning to ensure uniform high standard of hygiene.

On large farms, and in collecting centres where large volumes of milk(more than 5 000 litres) must be chilled quickly from 37 to 4 C, the coolingequipment of the bulk tanks may be inadequate. In these cases the tank ismainly used to maintain the required storage temperature; a major part of

the cooling is carried out by means of a heat exchanger in line in thedelivery pipeline (Figure 1.17).

Frequency of delivery to the dairyIn former times, milk was delivered to the dairy twice a day, morning andevening. In those days the dairy was close to the farm. But as dairiesbecame larger and fewer, their areas of collection increased and theaverage distance from farm to processing increased. This meant longerintervals between collections.

Collection on alternate days is common practice today in most of thelarge dairy countries with modern milk production. Collection every three or

even four days is not entirely unknown.Milk should preferably be handled in a closed system, to minimise the

risk of contamination. It must be cooled to 4 C as soon as it is produced

Fig. 1.18The influence of temperature

on bacterial development in raw milk.

1

2

3

10

100500

900

0,3

0 4 8 12 16 20 24 28

4 C

15 C

20 C

25 C

30 C

Million bact./ml

h


10/16


and then kept at that temperature until processed. Allequipment coming into contact with milk must be cleanedand disinfected.

Quality problems may arise if the intervals betweencollections are too long. Certain types of micro-organisms,known as psychrotrophic, can grow and reproduce below+7 C. They occur mainly in soil and water. Therefore, it isimportant that water used for cleaning is of highbacteriological quality.

Psychrotrophic bacteria will grow in raw milk stored at4C. After an acclimatisation period of 48 72 hours,growth goes into an intense logarithmic phase (F igure 1.19).This results in breakdown of both fat and protein of the milk.

This might be an important reason for off-flavours that may jeopardise thequality of products made from the milk.

This phenomenon must be taken into account in the planning ofcollection schedules.

Buffalo milkBuffaloes are the most common milk producer in Asia and certainareas of Africa. There are many different species and the dominanttype varies from region to region. The world population of buffaloes issome 150 million, of which 145 million live in Asia.

Most buffaloes are owned by farmers with small farms and aremerely a source of a little extra income. In India, it is commonthat a family owns one or two buffaloes. In northern India, herdsizes of 10 to 15 animals are common. This area also has a well-developed milk collection system. Outside large Indian cities largefarms with herds of 100 300 buffaloes are common.

Widespread in India, Pakistan and Southeast Asia, buffaloesare also common in Egypt, Romania, Turkey and Italy. In India,

Pakistan and Egypt, some 50 65 % of all milk produced is frombuffaloes.

It is estimated that 17 % of the worlds total milk production comes frombuffaloes. Only 6 % of the buffalo milk produced in India is processed, mostis used by the farmer or sold untreated as street milk.

Milk from buffaloes can be processed like milk from cows. However, itsthermal stability is lower, so mixed milk, a mixture of buffalo and cow milk, ispreferable for UHT treatment.

Yield and lactation periodThe milk produced during a lactation period may differ due to regional and

availability of feed. The buffaloes in India and China only produce 450 500kg per lactation period, while others,i.e.specialised milking farms at Indianuniversity farms produce more than 1 700 kg, and in Italy up to 3 000 kg.

The lactation period varies from 217 days in Egypt to 270 295 in India.

Secretion of milkLactating buffaloes secrete milk in the same way as other lactatingdomesticated animals. The anatomy of buffalo teats is slightly different fromcow teats. The muscle around the streak channel is thicker, and more forceis therefore required to open the canal. This is why the buffaloes are hardmilkers.

The milk is held in the upper, glandular part of the udder, in the alveoliand small ducts. Between milkings, there is no milk stored in the cistern.Hence, buffaloes have no cisternal milk fraction. The milk is expelled to the

Mo/ml

109

108

107

106

19x105

1 5430 2

"The critical age"

Days

Fig. 1.19Bacteria growth at 4C in rawmilk.


11/16


cistern only during actual milk ejection. The same phenomenon is seen inChinese yellow cows and yaks.

The composition of buffalo milk differs from that of cow milk. The biggestdifference relates to fat, as buffalo milk from some breeds may contain up to13 % fat. Buffalo milk fat has a higher melting point than cow milk, due toits higher proportion of saturated fatty acids. Phospholipids and cholesterolare lower in buffalo milk, and it is more resistant to oxidative changescompared to milk from cows.

Buffaloes produce colostrum during the first few days after calving.Colostrum from buffalo has a dry matter content of up to 30 % andcontains valuable proteins. The colostral period usually lasts three days,during which the composition of the colostrum gradually changes,becoming more and more like ordinary milk. Colostrum, should not bedelivered to dairy.

Some properties of buffalo milkAs can be seen from Table 1.1, buffalo milk is richer in most importantconstituents than cow milk.

The content of protein, lactose and ash is somewhat higher in buffalomilk than in cow milk. Buffalo milk contains vitamin A, but lacks -carotene,

which is present in cow's milk.

MilkingBuffaloes have been used in milk production for centuries. Milking buffaloesis not a difficult task. One should, however, take care not to simply applycow-milking techniques, as buffaloes require slightly different milkingmethods.

Hand-milkingHand-milking is the method most often used on small, family-run farms. It isimportant to use a smooth and comfortable milking technique. In hand-

milking, it is necessary to overcome the higher resistance in the teatsphincter.

Machine milkingBuffaloes have been successfully milked with machines for decades, incountries like Italy. Machine milking has during recent years become moreinteresting also for Asian and African farmers.

The udder and teats of buffaloes are different to those of cows, so aheavier cluster, higher operation vacuum and faster pulsation rate arerequired.

Sheep (ewe) milkAmong the numerous breeds of sheep, it may be difficult to define anyparticular dairy breeds, except by the purpose for which they are bred.Some breeds are mainly kept for production of meat and wool, but areoccasionally also milked. There are breeds considered as dairy breeds, buttheir production per lactation does not exceed 100 kg due to the conditionsunder which they are kept. On the other hand, milk production of somemeat breeds can be as much as 150 to 200 kg per lactation.

There are, however, some breeds that can be classified as dairy breedsdue to their high production of milk and good milkability. They include theLacaune of France, East Friesian of Germany, Awassi of the Near East andTsigai in the CIS, Romania, Hungary and Bulgaria. Production figures of 500

to 1 000 kg of milk per lactation have been reported for East Friesian andAwassi ewes.


12/16


Yield and lactation periodData on yields and lactation periods given by different authors show widefluctuation between the various breeds as well as within the same breed.Figures of 0,4 to 2,3 kg per ewe per day for yield and 100 to 260 days forlength of lactation should therefore be understood as a rough guide to lowand high averages.

Flock sizeIt is estimated that, other factors equal, 8 to 10 dairy ewes correspond toone dairy cow.

Flock sizes of 150 to 200 ewes are appropriate for intensive family farms,while flock sizes of 300 to 400 ewes may be suitable as a production unit.

Large-scale enterprises may have many thousands of sheep each. Thenumber of dairy animals kept in one flock, however, should not exceedabout 1 200, because of the labour demanding milking. Well-functioningand robust milking equipment and high efficiency of milking are of utmostimportance likewise as the quality of the management of the sheep.

An ewe is kept four to five years in a flock. The gestation period is aboutfive months, and most breeds average 1,5 to 2 lambs a year in poor areas

less than one. Ewe lambs can be bred from the age of 6 to 8 months.

Secretion of milkLactating ewes secrete milk in the same way as other lactating domesticanimals. Sheep milk is richer in all its important constituents as compared tocow milk (Table 1.1) and with nearly 30 % more dry matter. Variations insheep milk composition are due to most of the same factors as for dairycows,i.e.breeds, individuals and stage of lactation.

Ewes produce colostrum during the first few days after lambing.Colostrum has a dry matter content of up to 40 % and contains theimportant proteins, albumin and immunoglobulins. The colostral periodusually lasts three to four days, during which the composition of thecolostrum gradually changes, becoming more and more like ordinary milk.Colostrum should not be delivered to dairies.

Milk fatFat globules in sheeps milk range in size from 0,5 to 25 microns, but thelargest fraction is between 3 and 8 microns,i.e.nearly twice as big as thefat globules in cow milk. The fat of sheep milk has a higher content ofcaprylic and capric acid than fat of cow milk. This is the main reason for theparticular taste and aroma of milk products from sheep.

ProteinSheep milk is typical casein milk. It contains on an average 4,5 % of caseinand only around one per cent of whey proteins. The ratio casein/wheyprotein of sheep milk thus differs somewhat from that of cows milk, viz 82 :18 versus 80 : 20.

Some properties of sheep milkSpecific gravity is 1,032 1,040. This is due mainly to its high content ofsolids-non-fat. Acidity is high due to a high percentage of proteins. The pHnormally varies between 6,5 and 6,8.

MilkingThe anatomy of the udder of the ewe is different to that of the cow. Theudder of the ewe consists of two halves with one teat each.

While the cow is normally easy to milk, both manually and by machine,sheep are more difficult to milk compared to cows, both manually and by

Fig. 1.21Cross-section of one half of a

sheeps udder.

1 Alveolar tissue2 Milk ducts

3 Teat cistern4 Teat canal

1

2

3

4

Fig. 1.20Typical locations of teats onudders of sheep. The ideal position is

when the teats are located at the lowest

points of the udder halves.


13/16


machine. One important reason is that the teats of many ewes arehorizontally oriented. An ideal udder is one with the teats at the lowestpoints of the udder halves. Figure 1.20 shows examples of various udderconfigurations of sheep.

Some breeds have a small percentage of cistern milk (Figure 1.21). The

results of milking depend to a large extent of how well the let-down reflexworks.

As with cows, the release of milk is initiated by a hormone, oxytocin,which causes the muscle-like cells to compress the alveoli. This generatespressure in the udder. The milk let-down of sheep lastsonly for a short period, up to two minutes (as against upto 8 minutes for cows) depending on breed and stageof lactation.

Hand-milkingHand-milking is the method of milking most often usedin small herds. The efficiency of milking is very muchdependent upon the milk let-down. A good milker maybe able to milk 20 to 40 ewes with slow milk let-down (theLacaune breed) in one hour, while the same milker may be ableto milk 40 to 100 ewes per hour of sheep having fast milk let-down(the Manech breed).

Machine milkingDairy farmers with more than 150 ewes generally install machine milkingsystems to take the hard labour out of milking.

The working principle of milking machines for ewes is similar to thatdescribed for cows, except that milking vacuum is lower, and the pulsationrates are much higher.

The most common types of machine milking installations are churn,

mobile and pipeline systems (see Figure 1.22, 1.23 and 1.24).

Fig. 1.23 Mobile milking unit.

1

2

4

5

3

Fig. 1.22Churn milking system.1 Milk churn with pulsator2 Vacuum pipeline

3 Milk tank for cooling and storage4 Vacuum pump

5 Teat cup cleaning unit

2 3

6 1

5

4

Fig. 1.24 Pipeline milkingsystem.

1 Milk pipeline2 Vacuum pipeline

3 Receiver unit

4 Milk tank for cooling andstorage

5 Vacuum pump6 Teat cup cleaning unit


14/16


In a churn installationthe vacuum system is fixed and the churn unit ismovable. The churn, which holds 20 to 40 litres, is used for manualtransport of milk to the storage tank.

The pulsator can be mounted on the churn lid. A non-return valve in thelid allows air to be sucked from the pail.

A churn plant can have one to three churns per operator. The normalcapacity of an operator with two churns is 70 ewes per hour. This type ofinstallation is suitable for small flocks of up to 140 animals.

In apipeline milking installationthe milk line can be installed at high orlow level in the parlour. Milking capacity depends on the design of theparlour.

Themobile milking unitis suitable for small flocks and outdoor milking,and when ewes must be milked in different places. The installation has thesame capacity as that of a churn milking installation.

The unit consists of a complete vacuum system, power unit (electricmotor or combustion engine), cluster assemblies, milk container for 20 to40 litres and pulsation system, all mounted on a trolley.

During milking the trolley is placed behind four to eight ewes. The twopivoted bars are turned outwards behind the ewes, and the clusterassemblies are attached from the rear.

Goat milkThe goat was probably the first ruminant that was domesticated. Goatsoriginate from Asia and are now spread almost all over the globe. Goats arevery hardy animals. They thrive in areas where it may be difficult for other

animals. Unlike sheep, goats are not flock animals.There are numerous breeds of goat, but no specialised dairy breed.However, Saanen, Alpine, Toggenburg and Chamois breeds havebeen very successfully selected and bred for increased milk yields.Because of this, they have been exported all over the world for

purpose of being crossed with local breeds.

Cashmere and Angora are breeds known for the special wool theyproduce.

Yield and lactation periodIn a well-managed milk production herd, a goat can produce between 400and 1 300 kg milk per lactation. The length of lactation varies from 200 to300 days.

The hard, uncomfortable work of hand milking is eased by milking bymachine. However, a certain volume of milk should be produced or acertain number of animals should be kept to justify change to mechanicalmilking. For a family-sized goat milking operation, depending upon local

conditions at least 50 to 150 goats are required to reach an acceptableturnover. A business enterprise requires a larger number of animals, e.g.200 to 1 000 goats. An intensive and feasible production unit, family sizedoperation or business enterprise, however, requires not only appropriatemilking equipment but also effective management, feeding and breedingprogrammes.

Secretion of milkGoats secrete milk in the same way as other lactating domestic animals.

The composition of goat milk, like that of other species, is influenced byseveral factors. From Table 1.1 it appears that gross composition of goatmilk is almost similar to that of the cow. However, the ratio of casein towhey proteins in goat milk is narrower, 75:25, as compared to 80:20 forcow milk. The relative higher content of whey proteins may make goat milkmore sensitive to heating.

The pH of goat milk normally varies between 6,5 and 6,7.

Fig. 1.25The shape of the goatsudders.


15/16


16/16

16

Date post:	03-Jun-2018
Category:	Documents
Upload:	huynhnhatduat
View:	222 times
Download:	0 times

01 Primary Production of Milk

Documents