We have two dogs - a West Highland Terrier and a Tibetan Terrier?

The Westie is 7 months old and the Tibetan is 5 months old. When they do a poo the Westie's is solid but the Tibetan's is sloppy. Not exactly diarrhea but definitely not solid either. Now why would this be as to be honest her poo's never really been very solid and she eats exactly the same as the Westie?