What is the buzz of newborn puppies after artificial feeding?

There may be the following reasons for the humming of newborn puppies after artificial feeding:

1. I am very hungry. Because the nursing dog can't maintain its body temperature, it leads to hypothermia, and when it is hungry, it will purr.

2. The ambient temperature is too low, which causes the puppies to tremble.

3. The suckling dog can't urinate and purr by himself.

The above are several possible reasons for the buzzing of newborn puppies after artificial feeding. If the above reasons are eliminated, please contact the veterinarian for examination in time.