Did you know? Mother dog's stress can be passed down to her unborn puppies. Basically, when mother dog is stressed, stress hormones are released into the bloodstream. Now, normally, puppies are shielded from the effect of these stress hormones courtesy of a special enzyme that inactivates them at the level of the placenta. However, when the levels of mother dog's cortisol, are consistently high, some manages to seep through the placenta with the end result of reaching the developing fetuses.