How Cows Make Milk

Did you know that it takes 50 to 70 hours for a cow to turn grass into milk? Find out how cows make milk, what happens at milking time and all about automatic milking.


Before a cow can start producing milk, she must have delivered a calf. Cows usually produce one calf each year.

A cow starts to produce milk when her first calf is born, which typically happens when the cow is about two years old. Pregnancy lasts nine months and the cow is usually able to fall pregnant again about 100 days after her calf is born. This annual cycle ensures that calves are born at the best time of year.

She continues to produce milk for the first seven months of pregnancy. The farmer stops milking her two months prior to the birth so she can devote all her energy to producing her new calf.


Cows belong to a group of animals called ruminants, which have four stomach compartments that play different roles in digesting food and making milk. Other ruminants include goats, sheep, giraffes and camels.

To produce milk, cows need to eat a variety of grasses, clover and bulky fodder, plus food that’s rich in protein and energy.

cows eating grass in a paddock  

The four stomach compartments are:

The Rumen

The cow half-chews the grass before swallowing it into her first stomach – the rumen – which can hold about 100 litres of chewed grass. The grass mixes with water in the rumen and is broken down with stomach juices and microbes.

The Reticulum

The grass then enters the reticulum, where it’s softened and made into small wads called cuds. Each cud then returns to the cow’s mouth and is chewed 40 to 60 times – for about one minute.

The Omasum

The chewed cud is swallowed into the omasum, where it’s pressed to remove water and broken down further.

The Abomasum

The cud then enters the fourth stomach – the abomasum – and finally digested. The digested grass passes through the small intestine, where all the essential nutrients the cow needs to stay healthy and strong are absorbed.  

It takes 50 to 70 hours for a cow to turn grass into milk. Depending on the breed, a cow can make between 25 and 40 litres of milk a day.

Nutrients from the grass are turned into milk by four mammary glands in the udder. The milk is released from the udder through the teat, but this won't occur if the cow is stressed or uncomfortable. Suction from a calf or milking machine helps draw out the milk. The teat has a muscle called a sphincter which stops the milk dribbling out when the cow isn’t being milked.

For every litre of milk the cow makes, more than 400 litres of blood must travel around her udder to deliver the nutrients and water for making milk. A cow has about 45 litres of blood in her body, so her blood is continually travelling around her udder to help with milk production.


Dairy cows are usually milked twice a day in specially designed, electronically controlled milking sheds. Milking stalls in these sheds can be set out in a ‘herringbone’ pattern or on a continuously rotating platform called a rotary that allows the cows to easily and efficiently move through the dairy with minimal handling.

 In most dairy sheds, cows are fed hay, grain or special mixed feed rations while they’re being milked, which improves their health and ensures they receive the nutrients needed to produce high-quality milk. It also encourages them to come in to be milked.

It’s important that the cows are kept happy and relaxed to help them produce milk. Sometimes the farmer even plays soothing background music to help the cows relax!

Cows will wait at the gate to the milking shed so that they’re first in line to be milked. Once the farmer opens the gate, the cows make their own way into the shed and line up next to each other. The person milking stands behind the cows and moves from one cow to the next.

A suction cup on the end of a flexible milking line is fitted onto each of the cow’s four teats. The main milking machine uses a pump to create a vacuum, with a special controller that converts this into a series of ‘vacuum surges’ in each milking line. This cleverly sucks milk out of the teats in pulses, in much the same way as a calf does. The milk is drawn through the milking lines into stainless steel pipes that lead to a refrigerated storage vat, which cools the milk to four degrees Celsius. The milk is stored here until it’s collected by a milk tanker within 24 hours of milking.

Before accepting the milk, tanker drivers test it for freshness and quality to ensure it complies with all health standards. This is just one of the checks carried out to ensure that consumers receive a quality product.


Can you imagine a robot milking a cow?

It’s a reality in Australia, thanks to the development of automatic milking systems that make the entire milking procedure free of human assistance!

The cow voluntarily enters the milking shed for milking and is recognised by an electronic transponder. The suction cups are attached to the cow’s udder by a robotic arm and are removed after milking has finished.

The Australian-designed technology has huge potential to reduce the amount of time larger dairy farms spend on milking, freeing up the farm staff to concentrate on other farm and business management activities such as monitoring the performance of individual cows and the whole farm system.

Four Australian dairy farms are already using the automatic milking system with great success. Check out a farm using this technology by visiting