This same gradual switching of formulas should be done any time you change your dog's food. (eukanuba.com)
Try another brand, or a more gradual switch.) (littlebigcat.com)
Still, even with your younger child, you can make a gradual switch, going first to 2 % milk and then later switching again, this time to 1 % milk or skim milk. (verywellfamily.com)