Hi, this is Emily from MinuteEarth.
Supermarkets have lots of milks to choose from these days, many of which are the product
of blending up and straining various nuts and seeds.
Plain old milk milk, on the other hand, is also a strained product - it’s filtered
cow blood.
As weird as this seems, all mammal milk is, in fact, made from blood, because blood contains
lots of nutrients, and baby mammals need lots of sugar, fat, and protein to grow complex
brains and bodies.
But mammal mammas can’t just open an artery; that would be dangerous.
Plus, most of the useful nutrients in blood are too dilute and blood has too much iron
for most babies to process.
This is where the mammary gland comes in: It’s full of thousands of tiny sacs whose
walls have special cells that grab water and nutrients from passing blood, do some chemistry
on them, and pass them to the inside of the sacs where they mix together to become milk.
When a baby starts to suckle on the teat, its sucking pattern tells the mom’s brain
to the hormone release oxytocin, which attaches to the sacs, causing them to squeeze out the
tiny droplets of milk into the baby’s mouth.
Each mammal species tailors its blood-filtering recipe to the needs of its babies.
For example, to help their Arctic-dwelling pups pack on the blubber, hooded seal moms
produce a milk with 15 times the fat of cow milk.
Cottontail moms make high-protein milk for their bunny babies, allowing them to develop
their hopping muscles quickly.
The tammar wallaby can make two different types of milk in two different teats at the
same time - one high in sugars for a newborn in the pouch and one high in fat and protein
for her waddler.
And while selectively bred modern dairy cows don’t have a particularly wacky recipe for
their milk, they sure make a lot of it.
The current record holder - a Holstein named Aftershock - can produce a bathtub full of
milk every day.
That’s udderly impressive.
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