Like humans and other animals, dogs have a combination of beneficial bacteria and harmful bacteria that can be found inside of their gastrointestinal tract. In a healthy dog, there is more beneficial than harmful bacteria, and these bacteria are important in the process of digesting food. When food is digested, gas is released in small amounts and makes its way down to the colon to later be released through the rectum and anus. Gas can also be swallowed while eating, and some of this gas can contribute to flatulence but is mostly eructated (aka belched). In short, it is normal for dogs to burp and fart each day.
Certain breeds of dogs may burp and fart more than others. Brachycephalic breeds like the English Bulldog and the Boxer are known for their excessive flatulence. This is because of the conformation of their face and lower jaw. Due to their underbites, brachycephalic dogs tend to gulp and swallow more air with their food and water than other dogs, which contributes to more belching and farting. Special bowls and diets with wavy or half-moon shaped kibble have been reported to help decrease excessive air swallowing.
Flatulence can also increase due to problems with the gastrointestinal tract. When a new diet is abruptly introduced, the walls of the digestive tract can become inflamed and becomes a favorable environment for more harmful bacteria than beneficial bacteria. Stress can also contribute to inflammation, and high-fat foods can cause pancreatitis, a condition where the pancreas becomes inflamed and releases digestive enzymes that lead to severe gastrointestinal upset. Milk products may also cause increased flatulence because many adult dogs are lactose intolerant. Dogs tend to have sufficient amounts of lactase as puppies but then lose this digestive enzyme for milk products as they get older.