Raw milk that is fresh and clean,produced and handled under hygienic conditions that contains only small numbers bacteria the possesses a good keeping quality without being treated by heat. with the prescribed percentage of milk fat and solid non-fat. obtained by complete milking of a healthy animal,excluding that obtained with in 15 days before calving a 5 days after calving.
Nutritive value of milk
Milk is considered as a complete food, the best,ideal, and near complete food because it has almost all the essential nutrients-fat, protein, sugar, minerals and vitamins-in readily absorbable form and optimum proportions.
Nutrients in milk
Proteins-milk proteins are complete proteins of high quality.They contain all essential amino acids in appropriate proportion.
Minerals-all the mineral elements essential for nutrition are present in milk.Milk is excellent source of calcium and phosphorus.Milk is rather low in Iron,Copper and Iodine.
Physico-chemical Properties of Milk:
At first , milk might seem to be a simple white liquid.
But in fact, it is a complex mixture of a wide range of compounds important to the neonate.
The gross properties of milk include:
* Milk is an emulsion of fat globules, and
* a suspension of casein micelles (casein, calcium, phosphorous),
* all of which are suspended in an aqueous phase,
* that contains solublized lactose, whey proteins, and some minerals.
* Leukocytes in milk are part of the suspended phase.
Milk Composition
Milk composition receives a great deal of interest from a range of sciences, industries and applications. This is because the individual milk components can be considered from a number of perspectives, as indicated in the list below. In addition, the complex interactions of the milk components provide the basis for much of dairy chemistry or dairy food products manufacturing.
Views of milk components :
Simple separation techniques, such as centrifugation or acid precipitation, can be used to achieve crude fractionation of milk components. However, there are many physical and chemical interactions among the various components of milk. The result of all of these interactions is the complex fluid that we know as milk.The biochemistry of each component The mechanisms of synthesis of each component The role of each component in defining the physicochemical properties of milk The function of each component in the mammary gland The importance of each component to the nursing young The importance of each component in milk and milk products as foods for humans The factors that affect variability of milk component composition
In this module, each of the major organic components of milk is discussed with respect to the synthesis or origin of the component. Some specific milk components are synthesized in the epithelial cells from precursors absorbed from the blood. These synthesized components are then secreted into the alveolar lumen. Other components are transported through the epithelial cells with few or no chemical modifications before secretion into the lumen. All of the various components of milk can be found in the lactating epithelial cell, however, milk as we normally think of it, only exists as an accumulation of all the individual components as they are secreted from the cell into the lumen.
Structure of cow Udder
The milk is formed in the alveolus.There are a millions of them in each Quarter.The alveoli consist of the epithelium cells that derive nutritive substances water,vitamins and minerals.From the blood and then transform then into milk.
Milk composition
The Milk Composition section describes the chemical and physical properties and effects of pasteurization on the compounds in milk.A brief overview of the variation in milk composition is provided below as an introduction to this section.Topics covered are:
Carbohydrate (Lactose)
Fat
Protein
Vitamins and Minerals
Enzymes
Literature Related to Milk Composition
Unless otherwise stated, the information presented in this website refers to cow's milk.
In general, the gross composition of cow's milk in the U.S.is 87.7% water, 4.9% lactose (carbohydrate),3.4% fat, 3.3% protein, and 0.7% minerals (referred to as ash).Milk composition varies depending on the species (cow, goat, sheep),breed (Holstein, Jersey), the animal's feed, and the stage of lactation.Although there are minor variations in milk composition,the milk from different cows is stored together in bulk tanks and provides a relatively consistent composition of milk year round in the U.S.
Recommended Milking Procedures
Provide a Clean, Low Stress Environment for CowsA consistent operating routine for bringing cows and milking machines together is essential. Cows that are frightened or excited before milking may not have a normal milk letdown response in spite of an effective preparation routine. Hormones released into the bloodstream during periods of stress may interfere with normal milk letdown. A milking environment that chronically stresses cows may predispose cows to a greater rate of mastitis.
Removing hair from udders reduces the amount of dirt and manure that may adhere to the udder and contaminate milk. Udders with long hair are difficult to clean and dry. Milking wet and/or dirty teats increases the risk of high bacterial counts in milk and also increases the probability of new intramammary infection.
Before milking begins, hands should be thoroughly washed with soap and water and then dried. If hands become soiled during milking, wash and dry them again. Clean, dry, healthy hands minimize the spread of mastitis-causing organisms from cow-to-cow.
Check Foremilk and Udder for MastitisMastitis can be detected by using the hand to physically examine the udder and by using a strip cup or plate to examine foremilk prior to each milking. Correct use of a strip cup can be a valuable aid in detecting mastitis symptoms which include "clotty, stringy, or watery" milk. This observation should be made on each quarter of every cow at each milking. Because organisms may be spread by using unclean strip cups, strip cups should be cleaned and sanitized after each milking. A common procedure for forestripping in parlors is to strip directly onto the floor, followed by hosing the floor immediately. Milk should never be stripped into the hand because this routine spreads organisms from teat-to-teat and from cow-to-cow.
Wash Teats with an Udder Wash Solution or Predip Teats in an Effective ProductA common method of preparation in milking parlors is to use a hose (delivering sanitizing solution) and hands to remove debris from teats. Only the teats should be washed, as wetting the entire udder makes it difficult to adequately dry the udder before milking machines are attached. Milking wet udders and teats may lead to increased mastitis and elevated bacteria counts in bulk tank milk.
If a sprinkler pen is used, be sure that all sprinkler heads are working and properly adjusted. Adjust the time the sprinkler is running to the quantity of dirt and manure to be removed from the cows' udders. Sufficient drip drying time prior to entering the parlor is critical. Once cows are in the parlor individual paper towels should be used to finish drying the udder and teats. This procedure will help minimize the risk of new infections, stimulate proper milk letdown, and improve milk quality. For the rare cow that needs additional washing, use a hand-held hose but confine washing to the teats only.
Using a wash solution in a bucket and individual paper towels to prepare teats for milking is frequently necessary in stanchion barns. Individual paper towels are highly preferred because sponges and common cloths transfer mastitis-causing organisms to uninfected quarters and cows.
Producers with parlors or stanchion barns may elect to use predipping instead of washing when preparing cows for milking. Predipping works best when teats are relatively clean. The entire length of the teat should be immersed in the sanitizer. Predip should remain in contact with the teat for 30 seconds and then be thoroughly wiped-off prior to attaching the milking unit.
Dry Teats Completely with an Individual TowelRegardless of how the teats are prepared they must be dried. Dry with single service paper towels. As an alternative to paper towels, some producers use individual cloth towels. A separate cloth towel is used on each cow and towels are laundered, sanitized and dried after each milking. Washing teats without thorough drying leaves many organisms on the teats. During milking, water which contains mastitis-causing organisms can drip down the sides of teats and may be drawn into teat cups, exposing the teat ends to bacteria. Milking wet teats increases the likelihood of mastitis and reduces milk quality.
Attach Milking Unit within Two Minutes After the Start of StimulationThe milking machine should be attached as soon as possible after milk letdown occurs. Attachment should be done carefully to prevent excessive air from entering the milking system. Milk letdown causes maximum udder pressure approximately one minute after first stimulation and lasts about ten minutes. Most cows milk out in five to ten minutes. Therefore, attaching machines within two minutes after first stimulation makes maximum use of the letdown effect. There should be a consistent sequence of udder preparation and attachment of milking units so that units are attached within two minutes after the start of udder stimulation.
For comparison purposes, producers can use the following to evaluate their own operations:
| Production (pounds/day) | Predicted Average Milking Time (minutes/milking) | |
|---|---|---|
| 2X Daily | 3X Daily | |
| 50 | 6.5 | 5.6 |
| 75 | 8.0 | 6.5 |
| 100 | 9.4 | 7.5 |
From National Mastitis Council Annual Meeting Proceedings, Stewart et. al., 1993
Good management dictates that the person milking must be constantly alert to conditions that may spread mastitis organisms from cow-to-cow. Correcting such conditions assists in the production of high quality milk from healthy udders.
METHODS OF MILKING
Hand milking
Cows are milked from left side. after let down of milk, the milker starts milking teats either cross wise or fore quarters together and then hind quarters together or teats appearing most distended milked first few streams of fore milk from each teat be let on to a strip cup.
This removes any dirt from the teat canal and gives the operator a chance to detect mastitis.
Milking is done either by stripping or by full hand method.
Stripping is done by firmly holding the teat between the thumb and fore finger and drawing it down the length of the teat and at the same time pressing it to cause the milk to flow down in a stream. Grasping the teat with all the five fingers and pressing it against the palm does fisting or full hand milking.
The teat is compressed and relaxed alternatively in quick succession, thus the method removes milk much quicker than stripping as there is no loss of time in changing the position of the hand.
Further full hand method is superior to stripping as it stimulates the natural suckling process by calf and moreover the method exerts an equal pressure on the large teats of cows and buffaloes.
Many milkers during milking tend to bend their thumb against the teat.
The method is known as knuckling which should always be avoided to prevent injuries of the teat tissues.
Thus milking should always be done with full hand unless the teats are too small or towards the completion of milking.
The first few strips of milk from each quarter should not be mixed with the rest of the milk as the former contains highest number of bacteria.
CLEAN MILK PRODUCTION:
Milk containing dirt, dust, foreign materials high bacterial count and with off, flavour is called a contaminated milk.
Milk is contaminated by various sources like Udder, Exterior of cows body, milking barn, flies, milker, utensils etc.
On consumption of contaminated milk, one may get a’ number of health problems.
The sources for contamination are discussed below with their relative importance.
Udder:
Unsanitary conditions of milking barns and bedding of the animal causes bacterial growth.
Such bacteria may enter in to the udder through teat canal, which causes infection the udder like mastitis resulting contamination of milk. The fore milk may be discarded as it contains high bacterial count.
Complete milking should be done. Incomplete milking may lead to infection of the udder.
Exterior of cow’s body:
Bacteria present on the animal body may enter in to the milk at the time of milking.
Maintenance of, clean skin, washing flank and *udder with clean damp cloth before milk reduces the contamination from this source.
Milking barns:
Milking barns with good ventilation and neat flooring avoids contamination from this sources, Dry feeds or forage should be fed after milking.
Flies and other vermin:
External parasites like flies, lice; mosquitoes etc may have their entry in to milk.
So care should be taken to avoid these parasites from the barn by spraying fly spoors or by fly traps.
Breeding places for these parasites like stagnant water, moist atmosphere etc may be avoided.
Milker:
Milker is directly responsible in producing good quality milk.
Dirty hands and clothing of the milker may be the source of contamination.
Several bacterial diseases may transmit from the milker, or handler to the consumer through milk.
Persons suffering from diseases like T.B, Typhoid fever, diphthiria may not be employed for milking.
Dirty habits like smoking, drinking should be avoided.
Utensils:
Utensils are the containers or equipments in which the milk is handled, processed, stored or transported.
Clean sanitized, smooth copper free and dry utensils may be used for handling milk.
Milking method:
Wet hand milking and fisting causes contamination of milk.
Milkers in rural moisten their fingers with milk, water or even saliva, while milking.
This should be avoided. Wet hand milking should be avoided. Wet hand milking makes the teats look harsh and dry chokes, cracks and sores appear which causes contamination.
Twisting causes damages to the teat tissue which leads to udder infection. So dry hand milking may be practiced to avoid contamination of milk. Major contamination of milk is caused by bacterial entry.
So steps to be taken to, monitor such bacterial entry like avoiding unsanitary conditions of the barn. Milker, Utensils and avoiding unfair milking practices.
STEPS IN CLEAN MILK PRODUCTION
* The animal should be washed before milking.
* Washing of cows is best practice to minimize the bacterial entry.
* If calf is allowed for sucking, udder may be moist, cleaned with weak disinfectant solution later with fresh, clean water and wiped dry with a smooth and clean cloth.
* Hands of the milker should be clean and dry. Wet hand milking may result in high bacterial count in the milk.
* Nails of hands of the milker should be well trimmed.
* Milker should be free from all diseases.
* Dusty feed like Rice polish should not be fed to the animal at the time of milking.
* Milking barns should be well ventilated free from flies.
* Utensils used for milking should be clean, sanitized, smooth and copper free.
* Flavour producing feeds should be fed only after milking So that flavours will not appear in milk.
* The hind legs and the switch of the animal be tighted with the help of a milk man’s rope at the time of milking.
* Milk is kept in cool place to maintain the flavour and keeping quality.
* Milk should be covered with lids to avoid dust, dirt, entry hot, or cold, day light or strong artificial light, all at which tend to decrease milk quality.
* Raw milk with not exceeding 2,00,000 specific count in one ml of milk can be graded as very good raw milk
MILK HYGIENE
Milk is sterile when secreted into an uninfected udder. Contamination occurs during and after milking.
Exclude milk from clinical mastitis cases to avoid high bacterial counts. Use mastitis control routines at each milking to reduce the proportion of infected cows and clinical mastitis cases.
Avoid contamination from dirty udders and teats by good cow housing and grazing management.
Wash off visible dirt from udders and teats prior to applying the teat-cups. If udder washing is necessary, then drying afterwards is essential.
Individual paper towels for both washing and drying are preferable to udder cloths.
Clean and disinfect milking and ancillary equipment after use, paying particular attention to milk contact surfaces which are a main source of contamination.
The milk secreted into an uninfected cow's udder is sterile. Invariably it becomes contaminated during milking, cooling and storage, and milk is an excellent medium for bacteria, yeasts and moulds that are the common contaminants.
Their rapid growth, particularly at high ambient temperatures can cause marked deterioration, spoiling the milk for liquid consumption or manufacture into dairy products.
This can be avoided by adopting the simple, basic rules of clean milk production.
Udder infection
The essential requirements are to maintain udders free from infection (eg. mastitis); manage cows so that their udders and teats are clean; milk them in such a way that minimizes bacterial contamination; store the milk in clean containers and, wherever possible, at temperatures which discourage bacterial growth until collected. Simple and low-cost husbandry practices enable milk to be produced with a bacterial count of less than 50,000 per ml.
The golden rule of clean milk production is that prevention is better than cure.
udder infection
It is impossible to prevent mastitis infection entirely but by adopting practical routines it can be kept at low levels. Most mastitis is sub clinical and although not readily detected by the stockman, it will not normally raise the bacterial count of herd milk above 50,000 per ml.
Once the clinical stage is reached, the count may increase to several millions/ml and one infected quarter may result in the milk from the whole herd being unacceptable. It is important to detect clinical cases and exclude their milk from the bulk.
Other sources of contamination
Under normal grazing conditions, cows' udders will appear clean and therefore washing and drying will be unnecessary.
Otherwise, any visible dirt must be removed using clean, running water, individual paper towels or cloths in clean water to which a disinfectant has been added (eg. sodium hypochlorite at 300 ppm). If udder cloths are used, provide a clean cloth for each cow.
After each milking wash and disinfect them and hang up to dry. Disposable paper towels are preferable and more effective for drying after washing. When cows are housed or graze in heavily stocked paddocks, external udder surfaces are usually grossly contaminated with bacteria even when they appear visibly clean, therefore routine udder preparation procedures should be followed.
Whenever udders are washed they should be dried.
Cleaning milk production equipment
It is virtually impossible with practical cleaning systems to remove all milk residues and deposits from the milk contact surfaces of milking equipment.
Except in very cold, dry weather, bacteria will multiply on these surfaces during the interval between milking, so that high numbers ( 106 per m2) can be present on visually clean equipment.
A proven cleaning and disinfectant routine is required so that with the minimum of effort and expense, the equipment will have low bacterial counts as well as being visually clean.
The essential requirements are, to use milking equipment with smooth milk contact surfaces with minimal joints and crevices, an uncontaminated water supply, detergents to remove deposits and milk residues and a method of disinfection to kill bacteria.
Water supplies
Unless an approved piped supply is available it must be assumed that water is contaminated and therefore hypochlorite must be added at the rate of 50 ppm to the cleaning water.
Hard water (ie. high levels of dissolved calcium and other salts) will cause surface deposits on equipment and reduce cleaning effectiveness. In such case, it is necessary to use de-scaling acids such as Sulphuric or phosphoric, periodically.
Detergents and disinfectants
Detergents increase the 'wetting' potential over the surfaces to be cleaned, displace milk deposits, dissolve milk protein, emulsify the fat and aid the removal of dirt.
Detergent effectiveness is usually increased with increasing water temperature, and by using the correct concentration and time of application.
Detergents contain inorganic alkalis (eg. sodium carbonate and silicates and tri-sodium phosphate), surface-active agents (or wetting agents), sequestering (water-softening) agents (eg. polyphosphates) and acids for de-scaling.
Many proprietary, purpose-made detergents are usually available, but otherwise, an inexpensive mixture can be made to give a concentration in solution of 0.25% sodium carbonate (washing soda) and 0.05% polyphosphate (Calgon).
Disinfectants are required to destroy the bacteria remaining and subsequently multiplying on the cleaned surfaces. The alternatives are either heat applied as hot water or chemicals. Heat penetrates deposits and crevices and kills bacteria, providing that correct temperatures are maintained during the process of disinfection.
The effectiveness of chemicals is increased with temperature but even so, they do not have the same penetration potential as heat and they will not effectively disinfect milk contact surfaces which are difficult to clean.
When hot water alone is used, it is best to begin the routine with water at not less than 85°C, so that a temperature of at least 77°C can be maintained for at least 2 minutes.
Dairy disinfectants are sold as concentrates and in this form are often corrosive and damaging to the skin and eyes. They should always be so labeled, handled with care and stored out of reach of children.
Disinfectants should not be mixed unless specific instructions are given and disinfectant powders must be kept dry.
If any concentrated detergent and/or disinfectant comes in contact with the skin or eyes the affected area should be washed immediately with copious amounts of clean water.
Clean and disinfect the ancillary equipment such as coolers, foremilk cups and udder cloths effectively using hot detergent/disinfectant solution.Drain and store all the milking and ancillary equipment in a clean place such as the dairy of the milking premises.
Milking premises
The milking premises should have a dairy or suitable place equipped with a piped hot and cold water supply, a wash trough, brushes, a work surface, storage racks and cupboards and, if necessary, a vacuum pipeline connection.
In addition, it is advisable to have a dairy thermometer (0°C - 100°C), rubber gloves and goggles for use when handling chemicals.
Daily routines
Daily routines for cleaning and disinfecting vary with the size and complexity of the milking installation but will include methods of removing dirt and milk from the equipment followed by disinfection.
For hand milking, bucket and direct-to-can milking machines, basic manual methods of cleaning and sterilizing are adequate and effective.
For pipeline milking machines in-situ (in-place) systems are necessary.
Milk can become grossly contaminated from bacteria on ancillary equipment which must also be cleaned and disinfected effectively.
Coolers, either the corrugated surface or the turbine in-can, can best be cleaned and disinfected manually and stored in the dairy to drain.
Refrigerated bulk milk tanks can be cleaned either manually using cold or warm detergent/disinfectant solutions, or for the larger tanks, by automatic, programmed equipment.
In either case, a cold water chlorinated (50 ppm) rinse proceeds and follows the washing solution. Foremilk cups can be a potent source of bacterial contamination and need to be cleaned and disinfected after each milking.
They should then be stored in the dairy to drain.
It is important with any method of cleaning that the equipment is drained as soon as possible after washing for storage between milking.
Bacteria will not multiply in dry conditions but water lodged in milking equipment will, in suitable temperatures, provide conditions for massive bacterial multiplication.
Equipment with poor milk contact surfaces, crevices and large number of joints, remaining wet between milking in ambient temperatures above 20°C, should receive a disinfectant rinse (50 ppm available chlorine) before milking begins.
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