The milking equipment and its relation to mastitis
Malfunctioning of the milking machinery can cause an increase of mastitis prevalence in the herd, either by transmission of germs from one animal to another, either by damaging the teats.
Milking is an effort to obtain the largest quantity of milk in the least amount of time possible. On average, a cow is milked for approximately 4 minutes each milking. with high producing animals (15 litres of milk per milking) taking a bit longer: around 6 minutes and an additional minute for every 5 additional litres.
Over-milking can occur at the beginning of the process (from the time when the unit is connected until the milk flows), or at the end. In both cases the machine will operate without extracting milk, which allows the vacuum to cause damage to the teats. Good preparation of the udders is important, as well as installing a good-functioning automatic removal system. The removal time should be set at of 10-20 seconds and a milk flow smaller than 250 cc.
Some theories indicate that the front quarters finish milking before the rear ones, which means that they would always suffer over-milking. However, it is the rear quarters that are most frequently injured.
According to the UNE 68061 standard, the nominal vacuum level differs according to the type of milking:
- 48-50 kPa for container milking,
- 48-50 kPa in direct piping,
- 44-46 kPa in a mid-line milking parlour,
- 40-42 kPa in a low-line milking parlour.
During milking, the working vacuum in the claw during maximum milk flow fluctuates between 32 and 42 kPa (40 kPa is ideal, but it varies depending on the milk flow). Higher vacuum means lower milking time, yet excessive levels (above 42 kPa) can injure the tip of the teat.
The teat liner is the only component of the system in contact with the udder, and it transmits all of the forces applied by the milking machine to the teats.
It is easy for germs to adhere to the cracked surface of a worn-out liner, which promotes transmission of infections between animals. An incorrect design can have the same effect.
An important factor for keeping the teat in good condition is the use of teat liners with a diameter 1-2 mm smaller than that of the teats prior to milking.
It is essential for the liners to be elastic, in other words, they must be able to return to their original shape and size after having been deformed. There are tables that indicate the life, in days, of the liners based on the number of cows and milkings.
Requirements and basic features of teat liners
The teat liners should form an airtight seal at both ends of the pulsation chamber. The liner's mouth piece and barrel should fit onto the teat perfectly in order to minimize slipping or falling off. Milking should be as quick and clean as possible to prevent congestion or injury to the teat. They must be well aligned.
The pressure differences reached by the liner barrels when closing should be used to select liners with high or low vacuums. Slipping of the teat liners (air admitted between the ring and the teat, audible only 10-30% of the time) can promote the appearance of intra-mammary infections.
The pulsation maintains the blood circulation around the teat and is responsible for causing the teat liner to open and close.
The parameters to take into account are:
• pulsation frequency,
• pulsation ratio,
• duration of the phases.
Increasing or decreasing the pulsation frequency can cause the milking to be faster or slower. Variation in the pulsation ratio modifies the suction and massage phases, which can promote hemorrhaging, congestion, edema, etc. In all of these cases both the canal and tip of the teat can be damaged, causing the appearance of cracked sphincters and various degrees of hyperkeratosis.
There are two types of vacuum fluctuations: regular and irregular. Regular fluctuations are caused by the pulsation and remain constant during milking. Irregular fluctuations are caused by a variety of factors (insufficient vacuum reserve, slipping teat liners, etc.) and occur intermittently.
Vacuum fluctuations in the claw must be less than 7 kPa for a low line and 10 kPa for a high line. These fluctuations can cause impacts that project milk droplets towards the tip of the teats, with the resulting risk of transmitting infections.
Furthermore, excessive oscillations in the vacuum can cause hyperkeratosis, hemorrhage in the teat tips, congestion, and edema.