We have are dog eat a larger than normal meal the night before. Not eating the day of/during the hunt won't really affect their performance. However, you should keep your dog hydrated. We have a squeeze bottle, and we will generally go into the middle of a field, or field with no cover/plowed, sit her down and present it to her. It took her a while to get it, but they will. Our dog won't even eat steak before/in the car/during the hunt.