Why Do Dogs and Cats Fart?
Anyone with a pet knows the phenomenon: the dog lies sleeping on the sofa, and suddenly a smell fills the room that makes you want to leave immediately. Pet flatulence is a universal human experience — and biologically entirely explicable. The digestion of dogs and cats differs considerably from each other and from humans, leading to characteristically different flatulence patterns.
Dog Digestion: Why Some Breeds Fart More
Dogs are evolutionarily omnivores with a short digestive tract optimised for protein-rich food. Plant carbohydrates — especially legumes, corn, and wheat — are less well digested by dogs than by humans, leaving more undigested substrate for intestinal bacteria and correspondingly producing more gas. Particularly affected are brachycephalic breeds (dogs with short snouts): English Bulldogs, Pugs, Boston Terriers, and Boxers suffer more frequently from excessive flatulence — not only because of diet, but because their shortened anatomy causes them to swallow more air when eating and drinking (aerophagia). This extra air volume passes through the digestive tract and eventually has to escape somewhere.
Cat Farts: Silent, Rare, but Intense
Cats fart significantly less often than dogs — and when they do, almost silently. This is due to their anatomy: the cat's intestine is shorter and the anal musculature stronger, which favours quieter gas exit. Cats are obligate carnivores whose digestive system is optimised for protein. When cats receive carbohydrate-rich food — as in some cheaper dry food varieties with high grain content — their intestinal bacteria produce considerably more gas from the poorly digested carbohydrates. This explains why cats fed high-quality, protein-rich food show fewer flatulence symptoms. The notorious odour intensity of cat farts is due to the high sulphur content of the digested animal proteins.
What to Do About Pet Flatulence?
First check the diet: higher-quality food with a clear protein source and fewer fillers (corn, soya, wheat) reduces flatulence in many animals significantly. Fast eating is a common trigger — specially designed 'slow feeder' bowls with obstacles slow eating down and reduce air intake. Regular exercise supports intestinal motility in pets too. Sudden, severe bloating — particularly combined with restlessness, abdominal tension, or retching — can be a sign of a life-threatening gastric dilatation-volvulus (GDV) in dogs: this is a veterinary emergency. Chronic flatulence in a pet should always be investigated by a vet.
The Science of Pet Odour
The characteristic smell of dog farts differs from human flatulence mainly in sulphur content. Dogs digest large quantities of animal protein (including from dry food). The sulphur-containing amino acids it contains — methionine, cysteine — are broken down in the large intestine to hydrogen sulphide (H₂S), methyl mercaptan, and dimethyl sulphide. These compounds are perceptible in the tiniest concentrations: H₂S is detectable by smell from as little as 0.5 ppb (parts per billion). Interestingly, dogs and cats have different gut bacterial populations, leading to characteristically different gas mixtures — and smells. The dog's microbiome, in its composition, more closely resembles the human microbiome than that of the cat.
Did you know?
- Brachycephalic dog breeds (Pug, Bulldog) swallow more air when eating — a main reason for their more frequent flatulence.
- Cat farts are usually silent but intensely smelly — due to the high sulphur content from animal proteins.
- Hydrogen sulphide (H₂S) is detectable by smell from just 0.5 ppb — one of the most odour-intense substances known.
- A suddenly severely bloated dog abdomen with retching can indicate gastric dilatation-volvulus — a medical emergency.
Fun Fact
In a US survey of 1,000 dog owners, 48 percent reported their dog produced 'notable' flatulence at least once a week. 23 percent admitted to having blamed their own fart on the dog in front of a guest at least once. Dogs are thus the most widely used social distraction for unwanted bodily sounds.
Sources
- Bosch, G. et al. (2009). Dietary nutrient profiles of wild wolves: insights for optimal dog nutrition. British Journal of Nutrition, 103(S1), S18–S27.
- Suarez, F.L. et al. (1998). Insights into human colonic physiology obtained from study of flatus composition. American Journal of Physiology, 272(5), G1028–G1033.
- Deng, P. & Swanson, K.S. (2015). Gut microbiota of humans, dogs and cats. Nutrition Research Reviews, 28(2), 148–161.
- Glickman, L.T. et al. (1994). Non-dietary risk factors for gastric dilatation-volvulus in large and giant breed dogs. Journal of the American Veterinary Medical Association, 204(9), 1465–1471.