Just like a human fetus, a puppy fetus has an umbilical cord in the womb. That cord is critical to his development during gestation. After he's been born, someone needs to cut it. If his mother won't sever the umbilical cord herself, it's up to you to step in and free the puppy from the still-attached cord.
What It Does
The puppy's umbilical cord performs the same vital functions as a human's while the pup's in the womb. Essentially, this thin tube that connects to your puppy's abdomen supplies his body with the nutrients and oxygen he needs during gestation. Conversely, it also provides an exit point for waste generate by the fetus, like carbon dioxide. Until he's born, the puppy needs the umbilical cord to survive.
Birthing and Biting
When the puppy is born, the mother typically performs a ritual that helps the puppy transition from life in the womb to life in the outside world. He is born in a membranous sac that is part of the placenta, with the umbilical cord still attached to his abdomen. The mother clears the sac away from the puppy's face, severs the umbilical cord by biting through it, and eats the placenta. If you are helping your dog deliver a litter, don't allow her to eat more than two of these sacs, as they can make her queasy in excess. In the wild, the mama eats the placenta to eliminate the telltale smell of birth that predators would exploit.
Though dogs typically have the maternal instinct to birth their own puppies, if your dog doesn't bite through the umbilical cord, you need to step in and help -- otherwise, that opening into the puppy's body can become a gateway for infection. About 2 inches from the pup's body, tie a clean length of thread, fishing line or plain dental floss around the cord. On the side of that knot opposite the puppy, snip through the cord with a sharp pair of clean scissors. Dip the remaining end of the umbilical cord, the part still attached to the puppy, in iodine to clean it, and leave the thread tied on. The umbilical cord will fall off on its own within a few days -- this, like the section that you cut off yourself during delivery, can simply be thrown away. Neither the puppy nor the mother have any need for it.
Umbilical Hernia Help
Puppies can be susceptible to a notable umbilical-cord-related complication called an umbilical hernia. This genetic defect is the result of the opening in his abdomen not closing and healing properly after the umbilical cord falls out. The puppy's intestines can start to emerge from the hole and, while sometimes they can simply pop back in, they can kink and herniate, which is dangerous and painful. Your puppies should visit the veterinarian shortly after birth -- contact your vet to make an appointment as soon as they're born, Have the doctor check for complications. This defect can be fixed relatively easily with surgery, typically performed when the puppy is spayed or neutered.