If you have been feeding bread to a puppy, it is very likely the problem has been caused by
yeast in the bread
dough. Puppies (even older dogs) should not be fed bread, particularly if the bread dough had a high yeast content or has not been properly or completely baked.
Why is bread such a problem ... the enzymes in the yeast convert the sugar in doughy bread to ethanol (alcohol) and carbon dioxide. These are toxic to dogs.