If your dog has a gastrointestinal condition, initially, your dog may be placed on a fast for 24 hours, or in rare cases, for a maximum of 48 hours. Even during a dietary fast, make sure that plenty of water is available to your dog at all times. If possible, chamomile or fennel tea should be offered as well. With enough water your dog will pass the fasting period without complaints. Symptoms often wane before the third day. Please consult your vet before stopping your dogs feeding and beginning a fast.