[anonymous]

“Do dogs known to be having sensitive stomach? How did dogs in the wild survive?”

They didn’t, they didn’t live very long and suffered greatly.
“Dogs are not wolves”
http://skeptvet.com/Blog/?s=dogs+are+not+wolves

As far as transitioning foods, it depends on the dog. I have changed the brand of food cold turkey with no issues. Some dogs may have a loose stool or two.
Once I find a brand of kibble that agrees with the dog, I stick with it as a base and always add a little warm water.