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The milking machine was developed to reduce the hard work with hand milking. The ancient Egyptians tried to enter tubes into the streak canals to facilitate milking. However, it was not until 1830 the first tube milking machine appeared. Technical development after that would follow. Different types of milking machine principles were tested. Machines imitating hand milking were constructed. The machine that succeeded best was the one based on the suction principle. In 1851 use of vacuum was introduced for the first time and thereafter came the development of the one chamber teat cup. The two chamber teat cup was invented 1905 and a milking machine comparable with the machines of today was presented.
The milking machine constructed by Jens Nielsen 1892 (to the left) and the milking machine constructed by Anna Baldwin 1879 (to the right) (From T. Jansson. The development of the milking machine, 1973).
What kind of demands do we place on the milking machine? When the first milking machine was developed the demand was defined as efficient milk removal without causing any teat damage as well as being a tool for the farmer to reduce the labour related to milking. In order to fulfill these demands, the development of the milking machine is a multidisciplinary work where biologists, engineers and veterinarians collaborate.
How is the milking machine acting on the teat? The principle of machine milking differs from the principle of hand milking or suckling. During hand milking the milk is pressed out, while during suckling the milk is mainly pressed and to some degree sucked out. During machine milking the milk is sucked out by a difference in pressure between the inner wall of the udder and the liner.
During hand milking, the milk is pressed out.
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If a constant sucking is applied to the teat, blood and lymph would be accumulated in the teat. Therefore the milking machine is constructed so that sucking is interrupted by rhythmical motions (opening and closing) of the liner. Consequently, the teats are exposed to massage and congestion in the teat end is prevented.
During suckling the milk is mainly pressed out and to some extent sucked out.
All the parts in the milking unit must be treated as vital components in the whole system. For example, what is the importance of constructing a liner with optimal function if the pulsation frequency, vacuum level or dimensions of the milk tubes are inferior. However, for some better understanding of the system let's briefly discuss the importance and demands of the different components.
During machine milking milk is sucked out.
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The cluster (unit) consists of four teat cups (each having a shell, a flexible liner and a short pulse tube), a claw, a long milk tube and a long pulse tube. The liner consists of a head, a barrel and a short integrated milk tube. The liner is the only part of the milking machine which is in direct contact with the teat. Design of the liner therefore is highly important for optimal milking and teat treatment. Results from comparative experiments show that the liner design usually affects milking characteristics more than any other machine factor. The liner design can influence factors such as strip yield, liner slip, milking time, teat treatment and udder health. Liners must be designed to provide an airtight joint at both ends of the shell, provide a mouthpiece and barrel which will fit on the teat to minimize liner slips and cluster fall off. It must milk fast, as complete as possible, and reduce teat congestion and injury.
On the market there are an enormous number and range of liner designs, which all try to achieve the goals. As an example, the diameter of the mouthpiece lip ranges from 18-27 mm and the bore diameter from 20-28 mm. The reason why the design of the liners varies is mainly due to the variation in teat size and teat configuration among breeds. However, the range of the size within a herd is often greater than the average differences among most herds and breeds. It is worth noticing that if the liner is too short, the barrel will not have enough space to collapse under the teat leading to inefficient milking, while a too large liner might cause frequent slipping.
Teat cup cluster showing components.
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Besides different designs of liners, the material of the liner varies. Liners may be manufactured in natural, synthetic or silicone rubber. Natural rubber deteriorates faster due to contact with fat, resulting in shorter life time. Therefore, synthetic rubbers or mixtures of synthetic and natural rubber are more commonly used today.
The liner must be manufactured to withstand extreme stress. It pulses once every second, over 400 000 times per month, at the same time it is stretched as much as 20% or more than its original length. Therefore, regular replacements are recommended to ensure an optimum elasticity of the liner.
Cutaway view of liner.
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Principally, as soon as the teat enters the open liner it stretches to about 140-150% of its premilking length under the influence of the milking vacuum. During the milking the teat further moves into the liner the very first seconds of milking and no further movement can be detected until the flow ceases in that particular quarter. At the end of milking the liner sometimes crawls up along the teat and thereby obstructs the milk passage from the udder cistern to the teat cistern a phenomenon which in the long run will influence the milk production due to its effect on strip yield. Indeed, several factors influence the depth of the teat penetration. These factors are related to the teat, vacuum, liner, cluster, and friction between liner and teat. Optimal teat penetration is achieved when all these factors work together. The liner movement during a pulsation cycle results in milk extraction and udder massage. The pulsation cycle can be divided in four different phases a, b, c, and d.´
Pulsation cycle a = opening phase, b = milking phase, c = closing phase, d = massage phase.
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During phase a, the opening phase, the liner starts to open resulting in milk flowing from the teat. During phase b, the milking phase, the milk continues to flow. The following phase c, the teat cup liner starts to close and milk is prevented from flowing from the teat. The last phase, d, the massage phase or resting phase, the liner is kept closed.
In order to achieve an optimal milking efficiency and good udder health the rest phase should be at least 15% of the pulsation cycle or 150 ms. The liner wall movement is affected by the milk flow in such a way that high milk flows are related to a shorter massage phase, which in the long run influence udder health. Recent development work has resulted in the so called Harmony™ liner, where the massage phase is almost unaffected by the milk flow. The liner movement is also critical during the beginning and at the end of milking when the milk flow is low.
The force exerted by the collapsed liner causes the teat canal to close. In order to overcome the diastolic pressure in the blood vessels a pressure on the teat close to 10 kPa will be recommended in a situation where the pressure difference is about 50 kPa. Besides vacuum and pressure difference the liner plays an important role for massage efficiency. At a lower vacuum a soft and at higher vacuum a more stiff liner is recommended.
It can be concluded that in order to maintain good teat conditions and to create optimal milking performance the liner dimensions have to fit to the cows in the herd and the liner has to be adapted to the installation's vacuum level and level of the milk line. The liners should be mounted under moderate tension and have a relatively soft mouthpiece. In order to maintain its performance, liner replacement shall take place after 2500 milkings or 6 months in use, whichever comes first. Some types of liners have compounds which have a working life of 1000-1200 milkings.
Liner wall movement in relation to flow.
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The teat cup shells are usually manufactured in stainless steel. However, during the last decades constructions in plastic have appeared on the market. The demands on the shells are a shape to suit the particular liner design, it should be easy to handle during milking, and it should be constructed of material that stands hard handling such as kicking from the cow. In order to optimise the weight of the cluster the weight of the teat cup should be optimised accordingly.
The claw connects the short pulse tube and the short milk tube from the four teat cups to the long pulse and milk tube respectively. Different designs of claws exist on the market with variation in material, milk chamber volume (50-500 ml), air admission hole and "inner" design.
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The demands on the claw are manifold. The flow rates of high producing dairy cows are increasing which means the claw must handle larger amounts of milk. The claw should avoid cross infection among quarters of the same cow. One way of achieving this can be by separate quarter chambers or non-return valves. The air admission to the milk chamber helps to remove milk from the cluster, whereby its size and capacity are critical in milking situations where cows are high yielding and milk very fast. |
MC7 Claw
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A good example of a claw that has succeeded to fulfil many demands is the Harmony claw. In this claw the vacuum fluctuations are low even with a high milk flow, since the milk is removed from the bottom through the top of the claw via a central pipe. This means that there is always space left in the claw, which is not filled up with milk ensuring an additional buffer volume for vacuum. Milk is therefore continuously removed from the claw and the extracted milk is gently treated in a way that causes no increase in free fatty acids (FFA).
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The cluster consists of the four shells each including a liner all connected to the claw. The special demands on the cluster as a unit are to have a proper weight to reduce strip yields, slipping and fall off. Increasing cluster weight usually causes reduced strip yield, but increased slipping and falling off. In order to increase cluster weight some manufacturers increase the weight of the claw while others add some weight to the teat cups. The ideal situation is where most weight is put in the teat cups to give more equal weight distribution among the four quarters. However, of all the components in the cluster, the long milk and pulse tubes have the greatest effect on weight distribution, since insufficient tube alignment can cause imbalance in weight distribution.
In the Harmony concept the cluster weight is low, both the teat cups and the claw, improving the ergonomic situation for the milker. Along with this much development work has been done in order to find the best liner function together with a low weight cluster, still having sufficient milking performance. Consideration for a good milking performance has also resulted in increased outlet area for the short milk tube as well as an increase in volume of the short milk tube.
How are the machine parameters vacuum, pulsation ratio and pulsation frequency influencing the efficiency of milking? It has been experienced that vacuum levels above 50 kPa show little or no advantage to efficient milking. As can be seen in the picture below peak flow rate as well as strip yield increases with increasing vacuum levels. Since the incidence of hyperkeratosis of the external teat orifice and an increase in the degree of machine induced congestion and oedema also follows it is important to find the optimal vacuum level for each individual milking system. For example in low line installations vacuum levels around 42 kPa is comparable to 50 kPa in high line installations. To maintain vacuum stability is of highest interest when it comes to mastitis. Therefore cyclic vacuum fluctuations should be reduced, for example by air admission in the claw, by improving liner design to minimize liner slips and of course by removing teat cups gently at the end of milking. Before removing the teat cups from the udder, the use of a valve for vacuum is essential in order to reduce vacuum fluctuations.
Effect of vacuum level on peak flowrate (solid line) and machine stripping yield (broken line) (From Mein, In Machine milking and lactation, ed Bramley et al, 1992).
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Pulsation rate (c/min) |
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| Pulsation ratio (%) |
40 |
80 |
120 |
160 |
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50 |
100 |
108 |
127 |
137 |
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67 |
123 |
136 |
142 |
141 |
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75 |
134 |
142 |
141 |
140 |
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The effects of varying pulsation rates and ratio on peak flowrate* (Adapted from Mein, In Machine milking and lactation, ed Bramley et al, 1992).
*Comparative peak flowrates for a group of cows milked at a vacuum of 51k Pa (15 in Hg). Results are expressed as percentages of peak flowrate obtained at a pulsation rate of 40 cycles/min and pulsation ratio of 50%, i.e. liner more than half open for 50% of each pulsation cycle when tested with the liners stoppered.
Pulsation rate and ratio are parameters that also influence milking characteristics such as milk flow and milking time (See table above). Peak flow rate increases with increasing pulsation rate up to 160 cycles/min depending on the pulsator ratio. As a comparison, it has been reported that the calf uses a frequency of 120 cycles per minute during suckling. If the ratio is elevated to about 80% a fall in peak flow can be observed, probably due to insufficient degree or duration of compressive load on the teat. One recommendation for an effective pulsation is that the liner should be fully closed at least 15% of the pulsation cycle in order to overcome the congestion induced by the milking vacuum. From experiments it can be concluded that optimal pulsation ratio is 60:40 or 70:30 at a pulsation frequency of 60 cycles per minute.
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The demands on the milking equipment and milking parlours from an ergonomic point of view must be high, since dairy farming is one of the most burdensome activities within agriculture. High incidences of problems of the locomotor organs are found among dairy farmers. Milk producers often report difficulties in the elbows, lower back, hips knees, hands and hand joints.
The development started with replacing bucket milking plants by pipeline milking plants, which was a tremendous progress for the farmer's labour situation. Also, during 1970s automatic cluster removers were introduced. Since then development has continued and resulted in a lot of new products. The concept of Harmony includes a cluster with low weight which is easy to handle. Comparing the conventional milking unit and the Harmony™, cluster weight is reduced by more than 40%. The load on the milking operator is reduced and the milking routine time reduced. The concept of DeLaval carrier rail was the next step forward for stanchion barns. DeLaval carrier rail is a rail system that runs from the milk room through the whole stable.
In a study performed by the Swedish Farmers Health Service it was found that the use of DeLaval carrier rail reduced the health problems.
Milking with EasyLine reduced the problems in locomotor organs of the farmers.
In the milking parlour automatic cluster removers are common as well as the "service arm". Today it is also possible to have a moveable floor (Comfloor) in the parlour, adapted to the height of the milker.
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