My daughter is a vet and this is what she said:

There is a difference between a prolapsed uterus and vaginal hyperplasia,
which is what your hound had.
A prolapsed uterus occurs during straining to have pups and is not very
common in dogs, it is very common in cows.
Vaginal hyperplasia is just an incredible enlargement of the vaginal
tissue that only occurs during heat, as far as I know. That is also what
the textbooks will say.


CSSJR

Thanks you guys for all your help, We finally got everything back to normal. My dogs never really prolapsed all the way but the second one camereally close. I was so scarred. They ar both doing good, but I still do not really know exactly what caused it. Neither one of them are related, Maybe a long eay down the line, but no close relations if any. This actually happened after they both came in heat. Theyhad both come in heat about 2- 3 weeks before this happened, but the vet said to wait to see what happened next time beore we decided to fix them, becuase it never came all the way out becuase we caught it in time.. Thanks again for all of your information and details..