Hi Walt,
If he’s been eating it for a while, the transition will take some time, especially if he’s got issues with a leaky gut.
Start with a very small portion of the new food and mix it with a reduced portion of the old food. If he he’s doing well on the new food, leave him at that ratio for a few days. His stool will be the biggest indicator of how he’s handling the new food. Only increase the portion of the new food to the old when his stool is firm. Let the transition take as long as necessary, it could take two or three weeks or more. If he has some loose stool, a bit of plain, canned pumpkin helps a lot.
I would also consider adding digestive enzyme and probiotics to his food for a while. I’ve had great success with Swanson’s BioCore and Soil Based Organisms.
Zignature has lots of legumes which are notorious for their ability to cause gas and loose stool. If your pup doesn’t do well on the Zignature, you might need something without chickpeas or lentils.
Don’t stock up on fish based food. Delicate Omega 3’s are best added at the time that you serve it in the form of fish oil or sardines. Here’s a great article on rancid fats: http://www.whole-dog-journal.com/issues/15_12/features/Fats-Chance_20658-1.html. If you must buy fish based food, buy the freshest you can and smaller bags that you’ll use within a couple of weeks of opening. Once opened keep it stored in the original bag, with the top roles down and in an air tight container.
