Too much of any type of food or treat can result in some gastrointestinal upset for your pup. His case of diarrhea when eating Milk-Bones may also stem from an allergic reaction. Or the little guy might be ill, and the Milk-Bones are a coincidence.
Allergies and Overfeeding
The problem of overfeeding can be compounded in dogs who are allergic to whatever they're eating. Milk-Bones have milk as one of the main ingredients, along with an expansive list of others, such as flour, wheat and bone meal. If Fido is allergic to any of the ingredients in Milk-Bones, you may see no reaction from feeding one or two, but feeding him several may cause symptoms such as diarrhea, vomiting and itchy skin. If you're feeding way over the recommended amount, then allergies or not, diarrhea is a possibility.
Finding the Cause
Allergies require a vet. Make an appointment, and lay off the Milk-Bones. If he continues having diarrhea or at any time experiences other symptoms, such as dehydration or vomiting, contact your vet. If his upset tummy stops, feed him the recommended amount or fewer Milk-Bones per day. If he continues having problems, you might be looking at a food allergy, so make a vet appointment.