It can be hard on their digestive systems to switch foods often, especially puppies. I would research and find a brand you want to stick with permanently, or 2 brands to rotate -- but I would not rotate monthly because it usually takes a week to convert to a new food, and you would only keep the diet consistant for 2 weeks out of each month if you rotated monthly. Rotating every 3 months or so is probably okay, but I wouldn't choose more than 2 types.