The principle of machine milking is to extract milk from the cow by vacuum. The machines are designed to apply a constant vacuum to the end of the teat to suck the milk out and convey it to a suitable container, and to give a periodic squeeze applied externally to the whole of the teat to maintain blood circulation.
A milking machine installation consists of a pipework system linking various vessels and other components which together provide the flow paths for air and milk. The forces necessary to move air and milk through the system arise from the fact that it is maintained at a vacuum. Thus it is atmospheric pressure which forces air, and intra-mammary milk pressure which forces milk, into the system and the combination of these forces causes flow. To be a continuous operation it is necessary to remove air and milk from the system at appropriate rates. The air is removed by a vacuum pump at a constant rate.
The next slide shows the flow of air and milk during normal milking. The pulsator which is usually fixed on the bucket lid admits air intermittently and this passes along the long pulse tube to the teatcup chambers. To control the vacuum at a predetermined level air is also admitted to the system through a vacuum regulator which is fitted on the vacuum pipeline near to the milking points.
Principal types of milking machines. From: FAO, Animal production and health, Paper 78, Milking, milk production hygiene and udder health.
Efficient machine milking requires fast and complete milk removal without damage to the mammary tissue.
The following slide shows a cow’s teat in a milking machine teat cup.
There is a constant vacuum of 330-380 mmHg (45-50 kPa) applied at the inside of the liner to the teat end. The pressure at the outside of the liner alternates from vacuum (380 mmHg, 50 kPa) to air pressure (760 mmHg, 100 kPa). Alteration of vacuum to air (vac to air) in the outer jacket of the teat cup while constant vacuum is maintained within the liner and around the teat causes the liner first to open and then to collapse. When the liner is open (vac), the sphincter at the teat end is forced apart and milk flows. When air is introduced into the outer jacket (air) the vacuum at the teat tip causes the liner to collapse and squeeze the teat. The collapsing liner forces milk up the teat and back into the cistern, milk flow ceases and the teat end is squeezed, blood vessels become congested and circulation is reduced. During liner collapse (air) the teat is said to be given the chance to recover from the milking (vac) phase.
Usual pulsation ratios (vac:air) are 50:50 or 40:60. The pulsation rate, usually set around 48 to 72 cycles/min, has little effect on the speed of milking.
The milking process is the collection of tasks specifically devoted to extracting milk from an animal. This process may be broken down into several sub-tasks: collecting animals before milking, routing animals into the parlour, inspection and cleaning of teats, attachment of milking cluster to teats, extraction of milk, removal of milking cluster, routing of animals out of the parlour.
Cows are milked twice per day on most farms. However, 10% increased milk production can be obtained by milking the cows 3 times per day.
Cows housed in tie-stall barns are often milked in their stalls. Most cows milked in tie-stall barns are either milked with bucket milkers or pipeline milking systems. Milking cows in tie-stall barns is extremely labour intensive and requires much bending. The desire to reduce this type of labour has led to many types of milking parlour designs, in which the milker is at the level of the cow’s udder.
A good milking technique is essential for the production of safe raw milk.
Cleaning of teats before milking is important to remove both visible soiling (e.g. faeces, bedding, mud, residual post milking disinfectants) and bacteria which could contaminate the milk. It has been shown that the number of bacteria on teats is not necessarily linked to visual cleanliness so all cows should be cleaned, not just those with visibly soiled teats.
Before the attachment of the milking cluster, the following steps are recommended:
After the removal of the milking cluster, the teats must be disinfected by a post-dip solution.
Before the application to another cow, the milking cluster must be disinfected.
Milk must be cooled to under 6 °C within 2 hours of milking.
Animals producing abnormal milk or showing clinical signs of udder disease must be clearly identified. Milk from these animals must not be used for human consumption. The recommended means of excluding abnormal milk are:
milk affected animals last (with a full sanitizer cleaning routine after each milking)
milk into a dump bucket or dump line (with a clean, well maintained separate cluster and milk tube).
Tandem parlour are usually located on the end of a holding area with two entrance lanes similar to herringbone and parallel parlours. A gate at the entrance point between the holding area and the milking parlour holds the cow until an empty stall is ready. The parlour may be organized to allow the cows to exit in return lanes on either side of the operator area or cross over to a single return lane on one side.
Tandems are well suited to farms that take special care about observing individual cows and practice individual cow care in the parlour. The throughput of this parlour is less affected by variations in cow milk-out times and the disruptions from feeding grain in the parlour.
The number of stalls in a tandem parlour is usually limited to 4 to 8 for one operator and 8 to 12 for two operators. Stall lengths quickly add up to excessive walking time and difficulty in keeping track of distant milking machines.
This parlour type has a high stall use rate (7 to 8 cows/stall/hour).
This parlour type is not easily expandable, but if designed properly can be converted into a herringbone or parallel parlour with more milking stalls in the future.
One of the most popular types of parlour is the herringbone, so named because the cows enter and stand next to each other, but face away from the operator’s pit at an angle of approximately 30°.
Milkers attach the milking clusters to the teats from the side of the cow, and have better visual contact with the cow’s udder while she is being milked. It is usually easier to keep the milker positioned properly beneath the cow’s udder.
Herringbone parlours are located on the end of a rectangular holding area allowing cows to enter single file as a group directly into either side of the parlour. On completion of milking the cows exit single file by walking straight ahead and out of the parlour. Parlours with more than 12 stalls on a side benefit from rapid exit stalls to speed up the exiting process. In this case the cows walk straight away from the operator area in to a wide exit area. As the number of stalls on a side increases, it becomes more difficult to keep track of each cow and milking machine. In larger parlours the two rows of stalls may be arranged in a wedge or “V” configuration resulting in a wider operator area on the end away from the parlour animal entrance. This improves the visibility of units and cows from the other side of the operator area.
Herringbone parlour. From: DeLaval
The cows are placed at a greater angle from the operator (about 70 degrees) than in traditional herringbones but less than 90 degrees as in a parallel. This configuration usually eliminates the need for front positioners as used in a parallel. The sharp angle does not expose enough of the cow’s body to allow milking from the side. However, procedures and equipment developed for milking between the hind legs are used. Cows can exit single file to the front end of the parlour or to the sides of the parlour using a rapid exit type front.
The primary advantage of this parlour is that fewer milking units are needed and stall designs are simpler, both of which reduce the initial cost of the parlour.
Parabone parlour. Fonte: Enne Effe
Parallel parlours are similar to the herringbone parlors except that cows stand perpendicular to the operator pit and the cows are milked from the rear, between the cow’s hind legs. Advantages are that the cows stand closer together so the worker has to walk less between cows that are being milked.
Disadvantages are that the cow’s tail is often in the way and it may be a long reach for some milkers to grasp the cow’s front teats.
To assure that each position is filled in order, a series of interlocking fronts prevent a position from being used until the one next to it has been occupied. Most parallel parlours use rapid exit stall fronts and use dual return lanes. It is also more difficult to balance milking clusters on the udder in this parlour type.
Parallel parlour. From: Fullwood
With the rotary parlour, the platform on which the cows stand moves around, while the milkers stand in one location.
The advantage of the rotary parlour is that the cow movement functions are largely automated, freeing the operators to tasks more directly associated with milking. Rotary parlours typically require three operators: one for unit attachment, one to detach units and/or apply post milking teat dip and one to tend to any problems occurring while cows are travelling around (reattach units, tend to liner lips, etc.). This parlour type is not expandable. And the capital cost is usually higher per stall than for non-moving parlours. Because of these characteristics, rotary parlours are best suited to larger herds (>1000 cows).
One advantage of a rotary parlour is the very regimented and uniform.
Milking procedures will in general be much more consistent and efficient in a large rotary parlour (60 stalls) than in an equivalently sized herringbone or parallel parlour (double 30).
Rotary parlours usually use a ‘face-in’ configuration and are subject to all of the same disadvantages of a parallel milking parlour.
Rotary parlour. From: DeLaval
To alleviate the labour involved in milking, much of the milking process has been automated: many farmers use semi-automatic or automatic cow traffic control (powered gates, etc.), the milking machine has entirely automated milk extraction, and automatic cluster removal is available to remove milking equipment after milking. Automatic teat spraying systems are available. However, there is some debate over the cleaning effectiveness of these.
The final manual labour tasks remaining in the milking process are cleaning and inspection of teats and attachment of milking equipment to teats. Automatic cleaning and attachment of milking cups is a complex task, requiring accurate detection of teat position and a dextrous mechanical manipulator. These tasks have been automated successfully in the voluntary milking system.
Since the 1970s, much research effort has been expended in the development of the automated voluntary milking system.
Voluntary milking allows the cow to decide its own milking time and interval, rather than being milked as part of a group at set milking times. AMS requires complete automation of the milking process, as the cow may elect to be milked at any time during a 24 hour period.
The milking unit comprises a milking machine, a teat position sensor, a robotic arm for automatic teat-cup application and removal, and a gate system for controlling cow traffic.
The cows are permanently housed in a barn and spend most of their time resting or feeding in the loose-stall area.
When the cow elects to enter the milking unit (due to highly palatable feed that she finds in the milking box), a cow ID sensor reads an identification tag on the cow and passes the cow ID to the control system. If the cow has been milked too recently, the automatic gate system sends the cow out the unit. If the cow may be milked, automatic teat cleaning, milking cup application, milking, and teatdipping takes place. As an incentive to attend the milking unit, concentrated feedstuffs need to be fed to the cow in the milking unit.
The innovative core of the AMS system is the robotic manipulator in the milking unit. This robotic arm automates the tasks of teat cleaning and milking attachment and removes the final elements of manual labour from the milking process. Careful design of the robot arm and associated sensors and controls allows robust unsupervised performance, such that the farmer is only required to attend the cows for condition inspection and when a cow has not attended for milking.
Typical capacity for a AMS is 50-70 cows per milking unit. AMS usually achieve milking frequencies between 2 and 3 times per day, so a single milking unit handling 60 cows and milking each cow 3 times per day has a capacity of 7.5 cows per hour. This low capacity is convenient for lower-cost design of the robot arm and associated control system, as a window of several minutes is available for each cow and high-speed operation is not required.
Types of cow traffic
Elimination of labour
The farmer is freed from the milking process and associated rigid schedule, and labour is devoted to supervision of animals, feeding, etc.
Increased milking frequency
Milking frequency may increase to three times per day, however typically 2.5 times per day is achieved. This may result in less stress on the udder and increased comfort for the cow, as on average less milk is stored. Higher frequency milking increases milk yield per cow, however much of this increase is water rather than solids.
Perceived lower stress environment
There is a perception that elective milking schedules reduce cow stress.
The use of computer control allows greater scope for data collection. Such data allows the farmer to improve management through analysis of trends in the herd, for example response of milk production to changes in feedstuffs. Individual cow histories may also be examined and alerts set to warn the farmer of unusual changes indicating illness or injury.
Robotic milking procedure
The neck transponder is read when a cow enters the robot. If she doesn’t need milking, she is released.
Feed is dropped down in front of the cow if she is ready to be milked as a treat for coming up to be milked like getting dessert after eating your vegetables.
The brushes attached to the robot arm find the teats and clean them to remove dirt and debris.
Lasers on the robot arm locate teats and aid in attaching the teat cups.
Teat cups milk the cow and are detached when the quarter is empty of milk. Robotic milkers milk the udder by quarter not as a whole unit to make sure they are milked properly.
When all the teat cups have been detached, the robot arm sprays the teats with a peroxide based solution to help keep bacteria from growing on the udder and to prevent infections in the udder between milkings.
Between each cow, the teat cups and hoses are rinsed to make sure they are clean.
If a cow is sick and has been medicated, the robot discards her milk and disinfects the teat cups and hoses so that no trace of antibiotic containing milk is mixed with the saleable milk.
Three times throughout the day, the robot system takes a break from milking and washes and disinfects all the pipes and hoses to the milk tank to keep all the equipment clean and sanitary to assure the production of a safe and wholesome product.
Refrigeration is essential for maintaining the initial quality of milk. It stops or limits the bacterial growth and prevents changes in the constituents of milk used for processing.
Milk provides a medium in which different parameters are favourable to the growth of a number of bacterial species. The temperature is a parameter which can act either as a factor of inhibition or as a factor of proliferation. The temperature and time for which the milk is stored on the site of production therefore have a great influence on the growth of the bacteria present.
For milk with an initial bacteria count of 40 to 50,000 germs/ml kept at a temperature of 4 °C, the psychotrophic microorganisms (those capable of developing at temperatures below 10 °C) will develop to the detriment of the others.
Cleaning the milking system is one of the most important chores on the dairy. High bacteria counts usually are caused by dirty equipment or poor cooling of the milk. Cleaning the pipeline should begin as soon as milking ends, not after the parlour is washed.
The first step is to pre-rinse the system with water at 35-38 °C. Next, the system should be washed for 8-10 minutes with water at least at 71 °C and the correct amount of chlorinated cleaner. The water temperature should not drop below 43 °C during the wash cycle; if it does, fat may be redeposited back on the pipelines.
The next step is an acid rinse to neutralize chlorine residues and prolong the life of the rubber parts of the system. It also prevents mineral deposits, water spotting, and milk stone deposits. The water temperature for the acid rinse should be between 35 and 43 degrees.
The pulsator lines and main vacuum line from the trap to the pump also should be washed every 6 months. High bacteria counts occur because of dirty vacuum lines, especially if the trap keeps running over with milk.