
Hi Lucylu.
I have read previously that dark tarry stools can be caused from an infection or blood in the small intestine. Viral infections can irritate the wall of the small intestine temporarily causing it to bleed resulting in dark tarry stools.
However if your vet has checked the pups over and is happy, then I am sure there is nothing to worry about.
Let us know how they are tomorrow and if their poos are back to normal.
Take care
xxxx