Yesterday, neither my 7 month-old female bullmastiff, nor my one year-old male pitbull ate their breakfast. They've been on the same food for about four months. My cat and my other dog didn't lose their appetite, however. Later that evening, I fed them all dinner. Everyone ate except for Kindle, the bullmastiff. I worried a little, but she was acting her normal self and drinking water fine, so I just figured she may have had a tummy ache. This morning, she was the only one not to touch her breakfast. At lunch, I tried to feed her a late breakfast, and she didn't touch that either. Her feces don't look strange and she hasn't been vomiting or anything. Other than her loss in appetite, she is acting completely fine. She has had all of her shots. What could be wrong?