Why do small dogs live longer than large dogs?

Across mammal species, bigger animals tend to live longer. Within dogs it runs the other way. Breeds differ in body size by almost a hundredfold and in average life expectancy by a factor of two, and the large ones die younger. An analysis of death records from 74 breeds found no clear link between body size and when aging begins, and the baseline risk of dying was only slightly higher in large dogs. The main difference is speed: large dogs die young mainly because they age quickly.

Records from first-opinion practices in England tell the same story. Among more than 5,000 dogs that died, median longevity was 12 years, and heavier body weight went with shorter life. The Miniature Poodle, Bearded Collie, Border Collie and Miniature Dachshund were the longest-lived breeds, while the Dogue de Bordeaux and Great Dane were the shortest-lived. Crossbreds lived about 1.2 years longer than purebreds.

The role of IGF-1

Insulin-like growth factor 1 (IGF-1) is a hormone, made mainly in the liver in response to growth hormone, that drives growth in young animals. Its link to dog size is genetic. A study in Science found that a single version of the IGF1 gene is common to all small breeds and nearly absent from giant breeds, which suggests it is a major contributor to small size in all small breeds.

Blood levels follow the same pattern. When researchers measured serum IGF-1 in dogs from a few months to 17 years old and weighing about 2 to 73 kg (5 to 160 lb), levels fell with age in every group and rose overall with body weight, although the relationship differed between neutered and intact dogs.

Reduced IGF-1 signaling lengthens life in several laboratory species, which makes the hormone an attractive explanation for why small dogs outlive large ones. In dogs, though, the connection between IGF-1 and lifespan has not been directly proven. What is established is that large dogs have more IGF-1, grow faster and age faster. The rest is still being studied.

What faster aging looks like

If large dogs age faster, age-related problems should arrive earlier in their lives, and owners should plan care around the dog's biological age rather than its birthday. A seven-year-old giant breed may already need the monitoring a small dog would not need for several more years. Routine senior checks, including blood and urine tests and a look at joints, weight and heart, are worth starting earlier in large and giant breeds, with the vet setting the timing.

Cancer in large breeds

Cancer is a leading cause of death in dogs generally, and some large breeds carry a heavy burden. At one US veterinary academic center, 65% of golden retrievers examined after death between 1989 and 2016 had died of cancer, most often hemangiosarcoma or lymphoma. That was a referral population, which tends to include sicker dogs, but it matches the breed's long-standing reputation.

Osteosarcoma, an aggressive bone cancer, is mainly a disease of large and giant dogs. In a western Canadian study of large and giant breeds, Rottweilers and Great Danes had higher odds of limb osteosarcoma than Labrador Retrievers. Higher body condition score and previous lameness were also independently associated with the cancer, as was being a spayed female. Lameness in a large dog that does not settle within a week or two should be examined, and a painful swelling on a limb needs prompt attention.

Heart disease differs by size

The type of heart disease a dog is likely to get depends partly on its size. Small breeds more often develop degenerative mitral valve disease, a slowly progressive leak in a heart valve that many dogs live with for years under treatment. Large and giant breeds are more prone to dilated cardiomyopathy, in which the heart muscle weakens and the heart enlarges.

In both cases, early detection helps. A new heart murmur, a cough, faster breathing at rest, fainting or reduced stamina should prompt a vet visit. For breeds with a known predisposition, the vet may recommend screening with an echocardiogram or ECG before any signs appear.

What owners of large dogs can change

Size and genes are fixed. Several things around them are not.

• Keep the dog lean. In a lifelong study of 48 Labrador Retrievers, dogs fed 25% less than their pair-mates lived significantly longer and developed chronic disease later. Excess body fat was also linked to osteosarcoma in the Canadian study.
• Control growth in puppyhood. Feed a large-breed puppy food in measured amounts rather than free-feeding, and keep the puppy slim. The dogs in the Labrador study were restricted from eight weeks of age.
• Use joint support that has evidence. A 2022 meta-analysis found clear pain relief in osteoarthritis from omega-3-enriched diets and supplements, and no meaningful effect from glucosamine and chondroitin.
• Start senior monitoring early and ask about breed-specific screening for heart disease.
• Take lumps, lameness and weight loss seriously. Early investigation gives more treatment options.

None of this makes a Great Dane live as long as a Miniature Poodle. It does give the dog the best chance of reaching the upper end of its breed's normal range. The senior dog nutrition guide covers feeding as the dog ages.

Sources

1. The size-life span trade-off decomposed: why large dogs die young. The American Naturalist, 2013.
2. Longevity and mortality of owned dogs in England. The Veterinary Journal, 2013.
3. A single IGF1 allele is a major determinant of small size in dogs. Science, 2007.
4. Connecting serum IGF-1, body size, and age in the domestic dog. Age, 2011.
5. Association of cancer-related mortality, age and gonadectomy in golden retriever dogs at a veterinary academic center (1989-2016). PLoS One, 2018.
6. Risk factors for appendicular osteosarcoma occurrence in large and giant breed dogs in western Canada. Canadian Veterinary Journal, 2023.
7. Effects of diet restriction on life span and age-related changes in dogs. Journal of the American Veterinary Medical Association, 2002.
8. A 2022 systematic review and meta-analysis of enriched therapeutic diets and nutraceuticals in canine and feline osteoarthritis. International Journal of Molecular Sciences, 2022.