Dr. Universe,

How do humans get milk from a cow?

— John, 4, Colton, Ore.

Quite a few things have to happen for a cow to make milk. First, the cow has to eat lots of food, such as hay, grass or grain. You may have heard that a cow will regurgitate her food, or sort of spit it up, and then chew on it again.

A cow will chew this mashed up food, or her cud, so she can get all the good stuff out of it — protein, sugar, fat, vitamins, and other nutrients. Milk is actually mostly water, plus those good nutrients.

That’s what I found out from my friend Amber Adams-Progar, an animal scientist at Washington State University who studies cow behavior.

When the cow eats, those nutrients get absorbed into the cow’s bloodstream. The bloodstream is like a highway that moves the nutrients around the body.

In particular, the bloodstream helps deliver nutrients to the cow’s udder, which hangs down under the cow’s belly near her hind legs. It’s here in the udder where the milk is made.

Believe it or not, the cow’s brain is also involved in producing milk. When a cow’s body senses that she is going to have a baby, the brain will release certain chemicals. The chemicals help send out a signal for her body to produce milk.

When a calf is born, it will reach up to its mother’s udder to drink some milk. The milk has a lot of good ingredients the calf needs to grow up strong and healthy.

Of course, a cow doesn’t always have milk in her udder. She will only produce it when she has a baby. A cow has live young, hair and produces milk. That makes her a mammal. There are more than 5,000 mammals on our planet. You are a mammal, too.

Humans have actually been using milk from cows for thousands of years. They even figured out how to turn that milk into ice cream, butter and cheese.

In the past, some farmers would milk cows by hand and collect milk in small buckets. These days, some farmers use milking machines. They want to keep everything sanitary. They clean the cow’s udder and clean the milking equipment.

Most milking machines have about four cups that attach to a cow’s udder. These cups use suction to help release the milk. The milk flows down into a tube and gets collected in a huge tank. The person who is milking the cow will then clean the udder and milking equipment.

Adams-Progar also told me that some milking machines actually rely on robotics. On some farms, a cow can choose what time of the day she wants to go to the milking machine. A robot’s laser technology will line up her udder with the cups. Meanwhile, tiny sensors can help track her behavior.

You might say that a jug of milk all starts with a mama cow eating dinner. It’s something to think about the next time you go to the grocery store.


Have a science question? Ask Dr. Wendy Sue Universe, WSU’s resident science cat and writer, by email at Dr.Universe@wsu.edu, on her website at askDrUniverse.wsu.edu, via Twitter at @AskDrUniverse or at facebook.com/AskDrUniverse.

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