From Yorkies to Golden Retrievers and beyond, we all have our favorite breed of puppy, but how much do you really know about them?

In honor of National Puppy Day, which this year is on Sunday, March 23, we’ve gathered 20 interesting facts that you might not know about baby canines, which you can find below. 

1.  Each year, there are 6.2 million puppies born in the United States, according to She Knows.

2.  The most popular dog breed in the U.S. in 2013 was the Labrador retriever. 

3.  The second most popular breed in 2013 was the German shepherd.

4.  Puppies are born without teeth.

5.  Puppies are born unable to hear or smell. They are unable to smell until about three weeks after birth. 

6.  Newborn puppies spend about 90 percent of their first week sleeping. Puppies follow a sleep schedule similar to that of a newborn human. The average human newborn sleeps 16 hours in a 24-hour time period. Newborn puppies need about 14 hours of sleep in the same period.

7.  Puppies require five small meals a day.

RTR2XLE1 Bichon Frise puppies run in snow at Sinnington, northern England. Photo: Reuters

8.  Puppies' teeth begin to grow when they begin chewing, just like human babies. 

9.  At one-year-old, a puppy is no longer considered a puppy -- it's considered an adult! 

10. A one-year-old puppy is the equivalent of a 15-year-old human. 

11. Touch is the first sense a puppy begins to use. 

12. The nose prints of a dog are as unique as a human's fingerprints. 

13. Many puppies mistake a human smile for aggressive behavior if the person shows his or her teeth when smiling. 

14. Once their sense glands develop, puppies can smell up to 1,000 times better than a human.

15. Puppies don't open their eyes until they are nine to 12 days old.