Calsorb is a readily available source of calcium. You can give it to the mother during whelping as it will increase the muscles' ability to contract. It is readily absorbed into the blood stream and works very fast (faster than through foods with calcium or Tums). It is very helpful in cases of uterine inertia (when the muscles quit contacting) and can often start or strengthen the contractions. It is liquid given orally.
I get my information from Myra Harris who is a well known speaker on canine reproduction and puppy care. She has a yahoo group. Here is the link
http://pets.groups.yahoo.com/group/C...pro-PuppyCare/
It is one of the most informative groups on this subject I have seen.