Milking Machines and Milk Quality

Dr. Kent Hoblet, Chair and Dairy Extension Veterinarian, Ohio State University

Machine milking involves a complex physical interaction between mechanical equipment and living tissue. Moreover, this activity occurs two or three times daily for 300 or more consecutive days. As such, the milking machine may be a causative factor in the occurrence of mastitis in three ways:

(1) The machine may physically facilitate the transfer of bacteria from an infected gland to a noninfected gland either on the same cow or to another cow,

(2) The machine may cause damage to tissue, thus enhancing the ability of bacteria to gain entrance to the gland, and

(3) Abrupt vacuum instability within the machine may result in the reverse flow of milk droplets causing teat-end impacts. If bacteria are present, these impacts may permit their entrance into the gland.

The machine consists of five components. Typically, these include: (1) vacuum pump, (2) vacuum controller in most systems, (3) pulsation system, (4) milk transport system (pipeline or buckets), and (5) milker unit or cluster (bowl and teat cup assembly). To function properly, each of the above components must be of proper design and maintained in good working order. No one component is more important than another. Furthermore, it must be noted that an excellently designed machine kept in proper working order can be improperly operated. In fact, over 18 years of observation and troubleshooting herd mastitis problems, leads me to the conclusion that, all things being equal, excellence in operator performance is often more important than a perfectly functioning machine.

Pump - The pump removes air from the system to create a partial vacuum. A principle of cow milking is that milk should be removed under vacuum and then transported by gravity. Therefore, everything else being equal, a low pipeline system is preferred to a highline system. A general guideline is that any pipeline system's pump capacity should be a minimum of 35 cubic feet per minute (CFM), with an additional 3 CFM per milker unit.

Vacuum levels and vacuum controller - The National Mastitis Council (NMC) recommends an average vacuum in the claw during milking of 10.5 to 12.5" Hg. This normally indicates that the set or nominal vacuum on the system should be 12.5 to 13.5" Hg for low lines and bucket milkers and 14 to 15" Hg for high lines.

Measurement: Measurement of effective reserve and manual reserve on a regular basis are necessary to ensure that air extraction and vacuum controller operation are optimal. A guideline for good cow milking is that vacuum stability should vary by no more than 0.6" Hg when measured in the milk pipeline. Effective Reserve (ER) is essentially the amount of air that can be admitted into the system without changing vacuum more than 0.6" Hg. This measurement is made with the regulator functional. Manual Reserve (MR) is the same measurement made with the regulator inactivated. The fraction (ER / MR) x 100 = efficiency of the vacuum controller which should be > 90%. When variable speed pumps are used, only the ER can be determined.

An approximation of the effectiveness of pump capacity, vacuum controller, and piping system can be made by simulating a unit drop-off. In a properly sized and functioning system, the simulated drop-off of one unit (in a system with up to 16 units) should not result in > 0.6" Hg decrease in vacuum. There should be no observable override of vacuum levels.

Pulsation - Pulsators should be monitored regularly for function. The optimal pulsation ratio (the ratio of time spent in vacuum creation:air admission) is 60:40 (range 50:50 to 70:30), with an optimal rate of 60 pulsations per minute (range of 50 to 60). A frequent source of teat damage is failure to have adequate pulsation. This failure can be a result of holes in short and long pulsation air hoses, as well as malfunctions of the pulsator itself. Recording vacuum in the milker unit while cows are actually being milked is an excellent method of determining the adequacy of vacuum stability. In low line systems, we expect that there should be less than 1" Hg (2" in high line) vacuum difference between the pulsated and milk sides of the system and less than 2" Hg fluctuation recorded in the claw.

Cluster - There should be a provision for release of vacuum in the claw prior to removal of the milker unit from the cow. Synthetic rubber molded liners should be replaced every 1200 cow-milkings. Another guideline is to use liners no more than 90 wash cycles, even if the 1200 cow-milkings have not been exceeded. A frequent observation in herds with an elevated prevalence of Staphylococcus aureus infections is prolonged use of liners beyond these recommendations.

Automatic detacher - There has generally been a tendency to have the end of milking and the time delay for removal of the unit set such that udders are milked too dry. Such overmilking can result in trauma and hyperkeratosis (callous formation) at the teat end. Producers and others frequently (and mistakenly) refer to hyperkeratosis as prolapsed teat ends. Good guidelines to consider are that after the milker units are removed:

(1) Teat ends should not be reddened or edematous,
(2) There should be an easily obtainable stream of milk remaining in each quarter, and
(3) Cows should not flinch or kick when teats are touched after the milker unit is removed.

In summary, maintaining a properly functioning machine is an important component in achieving excellence in mammary health. Cold weather often seems to accentuate the role of the machine in udder health. Most Ohio farms could probably benefit from a greater investment in preventive machine care.