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A Closer Look at … Weddell Seal Milk
Milk and Mammals
Seals are marine mammals, and one of the characteristics of a being a mammal is to nurse the young. So, my question is: If seals - like humans - nurse their young, is their milk the same?
The answer is NO! There are some big differences. One difference is the percentage of fat in the milk; the other is the amount of milk human newborns and seal pups drink.
Let’s start off by talking about the milk we drink now – not the kind our mothers nursed us on when we were babies, but the kind we buy in the grocery store. Most Americans drink cow’s milk, but when you walk down the milk aisle at the grocery store, you see all different kinds of ‘cow milk’, right?
You might see
- ‘Whole’ milk
- ‘Low-fat’ milk
- 2% milk
- ‘Skim’ milk
So what’s the difference?
Whole cow’s milk has the highest fat - the others are between 0% and 2% fat.
Do you know how much fat is in the milk you drink? I drink ‘skim’ milk, which is less than 0.5% fat.
But, what did you drink when you were a baby?
Infants nurse on breast milk from their mothers. This milk is just right for their needs. It contains around 4% fat – along with other nutrients to help them grow.
Weddell seals also make milk that is perfect for their growing pups – but it is quite different from what a human baby needs. The milk from a Weddell seal contains around 60% fat – along with the other nutrients. Whoa! That’s a BIG difference!
That’s not the only difference – let’s take a closer look.
Let’s look at how much milk a seal pup and a human infant need to drink each day.
An average human babies drinks about 32 fluid ounces, or 1 quart, of milk each day. But seal pups are born much larger than human infants, and they grow a lot faster, so they need more milk. Can you guess how much more?
I think you might be surprised – they need 9 quarts of milk each day.
A human infant drinks 1 quart of milk a day, and that milk is 4% fat.
A Weddell seal pup drinks 9 quarts of milk a day and that milk is 60% fat.
Let’s take into account that the milk is not the same because Weddell milk has 15 times more fat than human milk. The average human infant consumes over 40 grams of fat every day, while a Weddell pup consumes 5,400 grams of fat every day. That’s over 135 times more fat per day!
Why do Weddell pups need so much more fat?
Remember that Weddell seals live in the coldest place on Earth, and they need to keep warm to survive. Adult seals have a thick layer of blubber, or fat, to keep their bodies warm and well-insulated, but pups are not born with this blubber layer. Weddell mothers nurse their pups almost continuously for the first 6 weeks of their lives, which is long enough for them to develop their own blubber layer. Since the pups are getting so much fat every day, you can imagine that seal pups grow pretty fast. They actually gain about 150 pounds in those first few weeks! Seal mothers have to do their part to help their babies survive!