Thanks, this is EXACTLY what a vet-tech I spoke to advised. Thanks again....By the way, the white, frothy upchuck is from Kennel Cough.
It is being taken care of now, too. The dog in question is a rescue from a high-kill shleter.
The best and easiest way to transition:
Days 1 through 3: 75% old food, 25% new food
Days 4 through 6: 50% old food, 50% new food
Days 7 through 9: 25% old food, 75% new food
Day 10: 100% new food