Modern Milking

Picture of the main components of an older milking machine.  There should be four attachments.  Photo credit Trevor Beaudry

One of the biggest technological advances in the history of dairy farming was the milking machine. Before its invention farmers milked all their cows by hand, which could take as long as 20 minutes each. This process was time consuming therefore limiting the number of cows the farmer could have. Today, with modern machines and milking parlor designs, it's possible to milk as many as 100 cows per person per hour. A major factor is that one person can operate many machines at a time, but this wouldn't have been a possibility without the development of a safe efficient milking machine. Milking machines were being developed throughout the 1800’s, but were not truly effective until the advent of the “Thistle” pulsator vacuum milker which achieved USDA approval in 1898.  So how does a milking machine work?

To understand how the machine works, you must first understand the anatomy of a cow’s teat. The teat contains three main parts: the teat cistern, a sphincter muscle, and the streak canal.

Basic illustration of the inside of a cow's teat.  Photo credit Trevor Beaudry

Milking a cow by hand manipulates these components. When you milk a cow by hand, you gently squeeze the milk out of the teat starting at the top and working your way to the bottom by squeezing your fingers one after another.  This causes the milk in the teat cistern to be pushed through the streak canal and the sphincter muscle that seals the teat from the outside environment.

Milking machines have essentially six components: a vacuum pump, pulsator, shell, inflation (basically a tough rubber liner), and two vacuum lines one that carries milk and one just for air. How it works is the flexible inflation goes inside the hard shell with a bit of air space. The inflation connects to the milk line while the air line connects to the shell. When the vacuum is turned on, the inflation is placed over the teat and the pulsator causes a vacuum, alternating between the milk and air lines. When the vacuum is applied to the milk line, the inflation squeezes the teat, which in turn, with the vacuum, causes milk to be expelled. When the vacuum then alternates to the air line, this shift causes the inflation to relax, removing pressure from the teat. This release of pressure is essential because it allows the teat cistern to refill with milk and prevents blood from pooling.

Basic cross section of the part of the milking machine that attaches to the cow's teat.  Photo credit Trevor Beaudry

Early vacuum based milking machines relied on constant pressure to draw the milk out of the teats. This resulted in a myriad of issues, not least of which was being uncomfortably to the cow. Two of the major issues attributed to the early non-pulsator machines were blood pooling in the teats along with damage to the sphincter muscle in the teat. Blood pooling caused discomfort and damage to the tissue while the teat sphincter is crucial in sealing the teat form outside pathogens.

Having described how humans and machines milk cows you’re probably wondering how a calf does it. Surprisingly, calves harvest milk very similarly to a pulsator style machine.   When suckling, a calf creates a vacuum on the teat, while also squeezing with its tongue. Squeezing the teat helps to open the sphincter muscle and release the milk. The calf can only suck for so long before it has to take a breath which causes it to relieve the pressure. This is imitated by the pulsator. Machine milking is actually much closer to how calves naturally harvest milk than hand milking which may contribute to the higher efficiency achieved by machines.

The advent of effective milking machines helped farmers milk more cows in a day, thereby enabling them to utilize labor more efficiently. Less time spent milking meant that labor previously used for milking could be used for things like cropping and fieldwork. The farmer could then either shrink their labor force or increase their herd size. This helped allow farms to get more efficient and less labor intensive. More time was then available to spend on genetic advancement and feeding.