I don't know if there are too many in a short time, but I do know that, if you keep on giving them to your pups, you should try to buy bones made in the USA. The ones that come from abroad have substances that may be hurtful to the dogs.
Probably your best bet is to ask the vet or go to one of the Internet info pages like:
http://vetinfo.com/
or
http://canismajor.com/dog/