Levente Czeglédi (2013)
University of Debrecen
Milk synthesis and secretion
The synthesis of milk starts with precursors entering the epithelial cell. The precursors are molecules, which will be used to build up the components of milk. These precursors originate from the digested feed and through the blood arrive to the udder (Figure 5.11). As these precursors from extracellular fluid enters udder cells through basolateral membrane, they will be involved in the pathway of milk fat, milk protein, lactose and other components synthesis.
The volume of milk is determined by the genetics of cattle, quality, quantity, nutrient value and digestibility of feed, housing, milking, climate and several factors. The regulation and synthesis of milk and milk components is controlled by enzimatic activity in the udder.
The volume of milk depends on the amount of lactose sythetized. The lactose is the most constant component, as its concentration in the milk does not change. Its total amount increases linearly as milk yield, but the concentration is 4.6-4.7 percent. As lactose is secreted into the cavity of alveolus, the osmotic pressure increases. The osmotic imbalance between the two sides of cell increases the water flow from blood to milk. The lactose synthesis is regulated by lactose synthesize enzyme. Lactose synthesis depends on the source of glucose, that one is controlled by availability of propionate and the propionate production in the rumen depends on energy concentration of feedstuffs.
During milk fat synthesis glicerol, acetate and butyrate are the major sub-components. The low fiber content of feed decreases acetate produced by the microbial activity in the rumen, thus depresses milk fat percentage. Approximately 50 percent of milk fat is originated of acetate and butyrate from activity in the rumen. These are used to form short-chain fatty acids, while about half of the milk fatty acids are synthesized in the udder and the second half is from fat content of feed. Roughage and concentrates eaten by the cow alters not only the fatty acid composition of milk fat but milk fat concentration as well.
Milk proteins are described before, their synthesis is regulated by different enzymes included in a certain pathway. Protein content of milk is high during the period of colostrum, but these immunglobulins are not synthetized in the udder but derives from the immune system transported by the blood.
The secretion of milk is a continuous process. For the production of one litre of milk, 400-450 litres of blood should enter the udder to transport nutrients and water. The produced milk is accumulated and the pressure is increasing in the alveoli, which is a signal to decrease the permanent synthesis. The secretion of milk is also decreased to a minimal level just before milking and during milking. The frequent milking increases yield, and get rid of pressure from udder. Cows with moderate milk yield are usually milked two times a day, 12 hours interval between milkings. High-production cows are milked in every 8 hours, it means that in the night as well. Several studies showed that four and as much as five times milking per day produces higher amount of milk than less frequent milking. As frequency increases the cost is higher as well, it can be assumed that five milking times per day, instead of four times, the labour, electricity, water, overall parlour operation and extra feed cost is more than the income of milk additionally produced.
Some accessories are described here, those have special function during and before the milking process.
Before entering the parlour, cows waiting in the collecting yard. The mud and dust on their udders depends on the climate, precipitation, housing system and bedding. Spraying units can be set on the collection yard or inside the parlour as well. Its function to clean the udders and during summer it cools the animal as well. Disinfection liquid can be sprayed after cleaning to prevent mastitis. Cooling sprays can be operated on upper parts of the yard to make a fine moisture on the surface of the body and as it evaporates cools the cow. Natural ventilation or ventilation equipments provide air movement to decreases heat stress.
The possibility to collect data of an animal requires a device operated by a computer to recognise the cow. A radiowave emitted from the unit and the signal is detected. Data is collected during milking, it activates the feeder in the parlour or provides information about the activity of the cow if it is attached to the leg. Pedometers are devices with great assistance and benefit in heat detection. Higher activity, more steps during the day warns the farmer to check the cow, whether it is in standing heat. It decreases calving interval and increases conception rate.
Feeders in parlour give concentrates to the cow during milking. Another possibility to fix feeders inside the barn (Figure 5.12). The amount of feed depends on the quantity of milk. If concentrates are fed in the parlour, cows ingest only roughage and not total mix in the barn.
During milking the milk flow and yield is recorded and equipment, called mastitis detector measures salt content of milk that changes the conductivitiy of liquids that reflects to the number of somatic cells in the milk (Figure 5.13).
The rotary parlour is like a carussel, the system has a round shape. It is a relatively new development, suggested for large stocks. Cows enter into a large turntable which moves slowly. The milkers do not have to walk on long ways as the cows arrive to them. There are two different systems: milkers and milking units are inside the circle or outside.
Milking clusters attached to the teats manually and removed automatically. There are possibilities to use concentrate feeders for individual nutrition.
Tanden parlour is one of the first parlour systems. The two rows of cows are parallel, animals standing in the barn and occupy the longest part of the side along the pit. Milkers can see the full length of the cow and attach the clusters to the teats from one side. The capacity of this type of parlour is limited because it requires relatively long pits and a lot of movement of milkers. Usually three or four stalls are either side of the pit, thus it is not suggested for farm with more than 80-100 animals.
An advantage, that each stall has an entry and exit gate, if the gates operate automatically, the cows after cluster removal leave the stall as gate opens and the next cow is allowed to enter to start milking. Consequently if there are good milking cows with slow milk release, it does not expand the duration of milking the stock as not all the cows at the same time in the parlour waits for the slowest one.
Chute parlour is very similar to tandem parlour, the design of the stalls are the same: cows standing parallel on both sides of pit. The main difference is that chute parlour requires less space, thus building of parlour saves cost. The number of stalls on each side is three or four and the cows enter to each side as a group and leave it together at the same time. There are no gates at each stall, cows waits for the slowest one during milking.
Herringbone parlour is a modified chute parlour, it looks like the skeleton of a fish. Cows stand in the stall at an angle of 30-35° to the side wall. It means that the milkers walk less distance in the pit. As shorter pit is used for the same number of cows, the capacity of this parlour is larger, in the largest ones two rows of 24 cows are milked. Cows have to wait for the slowest one that increase time spent in the parlour, which is more significant in a row of 24 cows.
Trigon parlour uses larger pit, it is advised to build for large stocks. Cows are milked in three rows and the design of parlour is a triangular. Cows stand in a stall in angle such a sin the herringbone parlour. The entry and exit gate functions as in herringbone parlour.
Polygon parlour is a four rows parlour, where the rows have a diamond shape. Cows in each row are milked as a single group. It is used for large number of cows, the disadvantage is that it is not possible to expand it.
5.13. ábra - Figure 5.13 Data collected by software in the milking parlour important for management decision
Robotic milking is the newest milking system. There is no need for parlour, no additional building is required. Milking robot is placed in the barn, cows voluntarily enters into the equipment, which recognizes the animal and depending on the number of daily milking adjusted it milks the cow or not. The number of milking is more compared to milking in tie-stall barns or in parlour.
As the cow arrives it is recognized by the computer as she wears an electronic tag and the laser of robot finds the teats, the arm moves and attaches the cups to each individual teats. The sensor during milking measures continuously some factors and collects to inform the farmer. Colour is measured to search for blood in the milk, conductivity is in close correlation to mastitis and milk flow and quantity is also detected. These data helps to manage a healthy dairy stock, prevents severe diseases.
There are several advantages of robot milking. It saves time for farmers, the robot clean and disinfect the udder itself, milk the cow and feed concentrates as it is required based on milk yield of cow. The precise nutrition adjusted to the daily change of need makes the milk production efficient and profitable. There is no collecting yard for cows, waiting for the parlour, so it saves time for the animals to express other activities such as feeding, resting and rumination. Most of the cows like to enter into the milking robot as there is no stress and she obtains the portion of concentrates.
Milking robot is worth to be invested in if the human labour is expensive and the service is easily available. Some extra time is needed for robotic milking when new cows have to be trained and some of the animals are not well suited for the equipment.