How Cows Make Milk

Read the following sections to find out how cows make milk:

How do Cows Make Milk?

How are Cows Milked?

What Happens at Milking Time?

How do Cows Make Milk?

A cow only starts to produce milk once her first calf is born. 

Cows typically have their first calf when they are two years old. Like humans, a cow is pregnant with her calf for nine months. Normally a cow has a calf once a year.

Once she is pregnant she continues to give milk for about seven months. The farmer stops milking her two months prior to the birth so she can devote all her energy to producing her new calf.

A cow usually produces milk for as long as she is milked.

Cows belong to a group of animals called ruminants. These animals all have four stomach compartments and each one plays a different role in digesting food. Other ruminants include goats, sheep, giraffes and camels.

It takes 50 to 70 hours for a cow to turn grass into milk and most cows give about 25 litres of milk a day!

Amazingly, for every litre of milk a 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 always on the move around the udder to keep making milk.

Before a cow can start producing milk, she must have delivered a calf.

To produce milk, cows must eat a variety of grasses, clover and bulky fodder, which make them feel full, plus food rich in protein and energy.

The four stomach compartments and their special functions are:

1. The rumen
When cows graze on grass they swallow it half-chewed and mix it with water in their first stomach - the rumen - which can hold about 100 litres of chewed grass. It is here that the digestive process begins. The rumen softens and breaks down the grass with stomach juices and microbes (or bacteria).

2. The reticulum
In the reticulum the grass is made even softer and is formed into small wads called cuds. Each cud is then returned to the mouth where the cow chews it 40 to 60 times (for about one minute).

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

4. The abomasum
The grass then passes to the fourth stomach, called the abomasum, where it is digested. The digested grass then passes through the small intestine, where all the essential nutrients the cow needs to stay healthy and strong are absorbed, and some are transported to the udder.



How are Cows Milked?

The nutrients from the grass are turned into milk by four mammary glands found in the udder. The droplets of milk are drained through an opening into the udder (called a duct) which is like a holding bag. The milk is released from the udder through the teat. Suction from a calf or the milking machine draws out the milk. The teat has a muscle called a sphincter which stops the milk dribbling out when the cow isn't being milked.

What Happens at Milking Time?

On most farms, dairy cows are milked twice a day in specially designed, electronically controlled milking sheds. Milking stalls are designed to allow for easy and efficient movement of cows with little need for individual handling. In most dairy sheds, cows are fed hay, grain or specially mixed feed rations while they are being milked. This keeps them healthy and makes sure they receive the nutrients needed to produce high-quality milk. It might not sound so delicious to us, but cows love this special feed, and it encourages them to come in to be milked.

Milking time is an enjoyable experience for the cows for many reasons. Sometimes the farmer plays soothing music in the background to relax the cows. It is important that cows are kept happy because they need to be relaxed to produce their milk.

Cows will wait at the gate that leads to the milking shed so that they are first in line to be milked. Once the farmer opens the gate, the cows make their own way into the milking shed.

There are two different types of milking sheds - herringbone and rotary. Herringbone sheds have two rows with a pit in the centre for the farmer to stand. The cows walk into the dairy and take their place on either side of the pit. One person can milk 80 cows an hour in a herringbone shed with 10 cows on either side. Some sheds have 20 or 30 cows on each side. In a rotary shed the cows stand in a circle on a raised platform which turns around while the cows are milked - like a slow merry-go-round! It takes about eight minutes to go around a full circle. If 50 cows fit on a platform, up to 350 cows can be milked in an hour.


                Herringbone shed                                                         Rotary shed

Most milking sheds are designed so that the cows stand on a raised platform for milking. This protects the farmer's back because he or she does not have to bend over to reach the cows' udders.

Once inside the shed, the cows stand beside each other and face in the same direction. The person milking stays behind the cows and moves from one cow to the next, working quickly and quietly to get the work done.

A suction cup on the end of a milking line is fitted onto each of the cow's four teats. This cleverly sucks milk out of the teats in pulses, like a calf does. The milk is drawn through the flexible milking lines into stainless steel pipes, and into a refrigerated storage tank called a vat, which cools the milk down to 4 degrees Celsius.

From the vat, the milk is collected by a milk tanker within just a few hours. Tankers have large, stainless steel refrigerated tanks that keep the milk clean and cold. Tankers have the capacity to carry up to 29,000 litres!

Before accepting the milk, tanker drivers test it for freshness and quality to ensure it is of a healthy standard. This is just one of the checks carried out to ensure that people are getting a quality product.

Robotic Milking

Top: a robotic milking machine
Bottom: robotic arm attaching the suction cups

Can you imagine a robotic machine that would do your homework for you? Well, that probably won't happen, but there are new robotic systems that can do the milking for dairy farmers! In Europe, over half of new milking machines involve robotic milkers. This machine milks the cows without any assistance from the farmer. The cow voluntarily walks to the milking shed to present herself for milking where she is recognised by a laser sensor. The suction cups automatically attach to the udder by a robotic arm and are automatically removed after milking has finished. Amazing!

The automatic milking system offers farmers a more flexible lifestyle as it will free up several hours a day previously spent milking cows, leaving farmers to concentrate on other farm duties, for example monitoring the performance of individual cows and the whole farm system. It also gives them a sleep in as it means no more 5.30 am wake-up calls for milking!

Cows know they'll be rewarded with grains to eat during milking and fresh pasture to enjoy afterwards. This often makes them want to be milked more, which means that cows that produce a large amount of milk can be milked more often (every 6 to 12 hours) compared to lower producing cows (every 12 to 24 hours).

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