Longevity for dogs 101

For the past months I've been deep diving into the topic of longevity for dogs to understand how can we help our best friends live longer and healthier lives. To figure that out, I intended to answer 3 fundamental questions:

1. How long do dogs live?
2. How age-related diseases manifest across dogs' lifespan?
3. How dogs' behaviour changes as they age?

The amount of information out there can be daunting so my primary goal was to put together a comprehensive and simplified guide about longevity for dogs. My secondary goal was to create a digestible bibliography that any newcomer to the dog longevity topic could study to get started.

This endeavour was more like a one-person journal club than anything else. This is the final result.

It's complicated! And it's difficult to give a definitive answer. However, we can take a look at veterinary studies analysing different populations in different countries to at least draw some high level conclusions.

Dogs go through various life stages as they grow from playful puppies to mature adults and finally into their senior years. These stages include puppyhood, adolescence, adulthood, senior and geriatric. The timing of these life stages is influenced by size, breed, genetics and lifestyle.

Fortunately, over the past few decades, average life expectancy for dogs has steadily increased. Studies show dogs are living longer now compared to some years ago. This rise is likely due to improvements in veterinary medicine, preventative care, nutrition, and other advances in canine health and wellbeing. Dog parents also have greater access to information and resources for optimal care of their pets.

While many factors influence lifespan, size impacts it the most. A dog’s weight is more predictive of lifespan than either height, breed, or breed group. In variation of body size, dogs far surpass all other domestic animals, with at least a 40-fold difference between the largest and smallest breeds. Among species, larger animals tend to live longer than smaller ones, however, the opposite is usually true between individuals of the same species.

Smaller dogs tend to live significantly longer than larger dogs across all breeds. Large dogs (above 50 kg) like Great Danes and Bouviers generally live for 6-8 years, while small dogs (below 10 kg) like Chihuahuas and Toy Poodles can reach 14-16 years.

Breed matters too. Certain ancestral breed groups, like mountain dogs, have lifespans shorter by 3-4 years. Some breeds are more prone to some diseases like cancers and heart problems that cut their lives short.

The decision to spay or neuter makes a big difference. Intact females tend to live shorter lives by 1-2 years on average, likely due to pregnancy complications and mammary cancers. However, spayed females live the longest of all by 1-2 years over intact females. For males, neutering brings a smaller longevity boost of about 6 months compared to intact males. Those spayed or neutered under 1 year of age gain the most longevity benefits. However, the optimal age for gonadectomy is still debated.

Genetics also play a key role. Mixed breed dogs live around 1-2 years longer than purebreds on average, likely due to hybrid vigor and reduced inbreeding. Across purebreds, breeds with lower inbreeding coefficients and higher genetic diversity can live up to 1 year longer.

Large breeds tend to have higher inbreeding, likely due to breeding practices involving fewer reproducing females. Variation in inbreeding between breeds does not appear to impact lifespan as much as size itself. However, inbreeding within breeds does reduce lifespan.

Lifestyle also influences lifespan. Obesity in pets is a condition of particular interest. It is the most common nutritional disorder in companion animals, and obese dogs have a reduced lifespan compared with dogs of normal body condition. Overweight dogs have lifespans shorter by 1-2 years compared to lean, ideal body condition. But underweight also foreshadows illness and reduces longevity so maintaining optimal weight is necessary for a long and healthy life.

Dogs receiving attentive preventive veterinary care live up to 1 year longer by catching problems early. More frequent dental cleanings add years by reducing bacteria and infection risk.

Higher household income is linked to better health, likely through increased veterinary care. However, income also associates with more diagnosed diseases, potentially reflecting greater diagnostic opportunities that catch issues before they impact lifespan.

Socialisation and mental stimulation are also important for behavioural and cognitive health. Social isolation is linked to higher mortality risk and lower overall wellbeing. Dogs living with other pets experience health benefits comparable to social integration for people. Dogs in unstable neighbourhoods with high turnover suffer mobility declines very similar to low socioeconomic status human populations.

Allowing dogs to roam freely decreases lifespan by 1-2 years from accidents and infectious diseases like parvo virus. Supervision maintains safety and health. Providing a secure loving home environment contributes greatly to longer, healthier lives.

While genetics and breed traits play a role, lifestyle and preventive care choices also greatly impact how long dogs live. Understanding these factors helps us make informed decisions to nurture our four-legged friends. When it comes to canine longevity, proactive care and love are key.

Dogs go through various life stages as they mature from puppies to senior dogs. The timing of these life stages is influenced by size, breed, genetics and lifestyle.

Across breeds, smaller dogs live longer than larger dogs on average. Inbreeding within breeds also impacts morbidity, with less inbred dogs tending to be healthier. Intact males have slightly lower mortality than intact females across most ages. However, spayed female dogs clearly live longer than neutered males or intact dogs of either sex. Overall, the effect of neutering on lifespan is greater than the effect of sex.

Both body size and inbreeding contribute significantly to breed differences in morbidity, even after accounting for age. Smaller, less inbred breeds require less veterinary care and have lower morbidity rates than larger, more inbred breeds.

As dogs age, their risk for certain health conditions changes dramatically. While young dogs commonly suffer from infections, trauma, and developmental issues, senior and geriatric dogs become more susceptible to chronic degenerative diseases.

Understanding the changes dogs undergo during each phase allows us to provide tailored care as they age.

Puppyhood

Puppyhood lasts from birth until approximately 6 months of age. During this time, puppies go through rapid development and growth. Key milestones include weaning, socialisation, learning bite inhibition, housetraining and basic obedience. Puppies have especially high energy levels and require a lot of stimulation and training at this stage.

While not caused by aging, some dogs are born with congenital defects that often require lifelong management. Early detection aids these lifelong conditions.

Puppy mortality is relatively high, with around 15% of puppies dying before 6 months of age. Trauma, infections, and congenital defects are common puppy killers. However, with proper care, socialisation, vaccination and veterinary attention, most puppies survive to adulthood.

Adolescence

Adolescence in dogs spans 6 months to 2 years of age, though the exact timing varies by breed and size. This is when puppies transition to adulthood both physically and mentally. They experience their first heat cycles, reach full adult size, fill out muscularly, and gain reproductive capability during this phase. Adolescent dogs are often bolder, more independent, energetic and distractible as they explore their world. Ongoing socialisation and training is crucial at this stage.

Young dogs commonly succumb to infectious diseases and gastrointestinal illnesses before their immune systems fully develops. However, vaccines largely protect puppies these days. Minor behaviour problems also frequently emerge in adolescence but tend to resolve with maturity and training.

The risk of mortality drops off substantially once dogs pass the crucial puppy stage. However, adolescent dogs may still occasionally die from trauma, infections, gastric dilatation and volvulus (bloat), and behaviour problems leading to euthanasia.

Adulthood

Dogs reach full adulthood around 1-2 years of age, though giant breeds may take up to 3 years. Adulthood encompasses the prime years where dogs are at their physical and mental peak. Energy levels stabilise, though exercise needs remain high. Training is easier as adult dogs have better focus and impulse control. This stage lasts approximately 1-6 years depending on breed, size and genetics.

In early adulthood, dogs may develop some orthopedic conditions like cranial cruciate ligament rupture (partial or complete tearing of a key knee ligament). However, osteoarthritis risk increases substantially with age as joint cartilage progressively deteriorates. Cardiovascular disease risk also rises dramatically in later life. Degenerative mitral valve disease (leakage of the heart's mitral valve) is very common in small breed senior dogs while large breeds are prone to dilated cardiomyopathy (enlarged, weakened heart muscle) with age.

In adulthood, mortality rates are generally low. However, some breeds susceptible to cardiovascular disease may die prematurely of heart failure. Orthopedic injuries also claim a small proportion of adult dogs. As dogs near seniority, cancer risk starts rising, resulting in increasing mortality.

Senior

Senior age starts around 6-8 years for most dogs. Giant breeds become seniors earlier while smaller dogs transition later. Signs of aging include slowing down, more sleeping, graying fur and minor cognitive changes. Despite some slowing, health is generally still good in early senior years. Additional vet visits, screening tests and monitoring help catch problems early.

Endocrine disorders become more likely as dogs’ metabolic, thyroid, and adrenal systems decline. Diabetes mellitus, hypothyroidism (under-active thyroid), and hyperadrenocorticism (overactive adrenal glands) occur more frequently in mature adult and senior dogs. The risk of neoplasia, especially malignant cancers, also increases exponentially with age. By 10 years old, around 35% of dogs develop cancer, rising to over 50% by age 15.

Cognitive decline and behavioural changes emerge in senior dogs as well. Disorientation, altered social interactions, housetraining issues, and sleep-wake disturbances are hallmarks of canine cognitive dysfunction syndrome, which affects over 50% of dogs over 15 years old.

The incidence of ocular conditions like cataracts and glaucoma also increases substantially with age. Over 75% of dogs develop lenticular sclerosis (hardening of the lens) by age 13, which can progress to visually significant cataracts. Age-related retinal degeneration can also impair vision.

While the total number of age-related morbidities accumulated does not differ between breeds, specific conditions making up those morbidities do vary across breeds. For example, mitral valve disease predominates in Cavalier King Charles Spaniels while Bernese Mountain Dogs are prone to histiocytic sarcoma (malignant tumors).

Most canine deaths involve euthanasia (86-87% across studies). This artificial foreshortening of lifespan often occurs when quality of life significantly declines. Euthanasia spares dogs a painful demise. However, dog parents and veterinarians must balance quantity and quality of life when making this difficult decision.

In senior dogs, the risk of euthanasia rises as chronic conditions accumulate. Over 20% of senior dogs are euthanised due to old age, cancer, and organ failure. Cognitive dysfunction and arthritis also commonly prompt euthanasia to alleviate discomfort.

Geriatric

At around 10 years and beyond, dogs enter the geriatric stage. Health issues are more prevalent, though individuals vary widely. Mobility, senses, memory and energy continue declining. Close monitoring and specialised care helps ensure continued quality of life. The geriatric period lasts until the end of a dog's life.

In aged geriatric dogs, multiple body systems often suffer functional decline. Kidney and liver failure become more likely as cellular metabolism and perfusion decrease. Dental disease from years of gingivitis and periodontitis is very prevalent. Urinary incontinence increases in spayed females due to urethral muscle weakness. Immune dysfunction from lifelong accumulated damage also develops.

By geriatric age, over 50% of deaths result from euthanasia. Severe mobility issues, cognitive decline, cancer, and organ failure often lead to euthanasia to prevent undue suffering at end of life. However, a minority of dogs die naturally if dog parents choose to let diseases run their course.

Overall, while the specific conditions vary, senior and geriatric dogs universally experience higher rates of morbidity and functional impairment compared to their younger counterparts. Understanding how age-related problems emerge across a dog's life prepares dog parents to optimise care.

As dogs go through different life stages, it is normal for their behavior and personality to change as well. Recent veterinary research has provided insights into these age-related shifts in temperament and cognition. Understanding how dogs' behaviour evolves over their lifespan allows us to provide care tailored to their needs at every stage.

Studies found some personality traits like activity and independence gradually decline from puppyhood into adulthood. However, other traits like novelty seeking remain stable until middle age when they diminish. Problem orientation increases during adolescence and early adulthood before leveling out. There are also individual differences, with some dogs changing more drastically.

While these age-related personality and behavior changes occur on an individual level, research has also revealed some overall trends in how dogs' temperaments evolve over their lifespan.

Looking at group changes across life, activity and novelty seeking decline most in middle age. Problem orientation, meanwhile, increases substantially during adolescence and continue rising into adulthood before stabilising.

As dogs age, they may interact less with people, sleep more during the day, and show less interest in play or walks. Some elderly dogs become anxious or disoriented in familiar environments as cognitive changes occur.

Recent research has revealed some overall trends in how dogs' activity levels change across their lifespan. Studies have found that activity declines most noticeably in middle age for dogs. This aligns with the idea that age-related changes correlate with the proportion of lifespan completed rather than exact years alive.

When looking at environment, research showed rural dogs are generally more active than urban or suburban dogs, especially in youth. However, these activity differences based on housing environment diminish in older dogs. Additionally, larger dogs were found to be more active than smaller dogs on average, but this size difference did not vary substantially with age.

Estimates vary, but somewhere between 14-22% of geriatric dogs develop more severe behavioural changes consistent with canine cognitive dysfunction syndrome (CCD). This involves progressive neurodegenerative changes in the brain leading to decline in cognitive functions like learning, memory, and awareness. Dogs with CCD may fail to respond to commands, have accidents in the house, or get lost in familiar areas. They often pace, wander aimlessly, or stare blankly at walls. The acronym DISHA summarises the common signs of CCD: disorientation, altered social interactions, sleep-wake cycle disturbances, housesoiling, anxiety, and changes in activity levels.

• Disorientation → Dogs may seem confused about their surroundings, get lost in familiar places, stare blankly, or have decreased response to stimuli.
• Alterations in social interactions → Dogs may show less interest in attention, fail to recognise familiar people, or have increased irritability.
• Sleep-wake cycle disturbances → Dogs may be restless at night, wake their pet parents, or sleep more during the day.
• Housesoiling → Previously housetrained dogs may eliminate indoors or lose their signalling to go out.
• Anxiety → Dogs may vocalise, pace, or show fear and phobias to sounds or situations.
• Changes in activity levels → Dogs may seem apathetic and disinterested or exhibit repetitive movements.

Other age-related health issues impact the development and severity of CDS in senior dogs. One of the most significant factors is hearing loss, which becomes increasingly common as dogs age. Over 60% of dogs over the age of 10 have some degree of hearing impairment. Deafness prevents dogs from perceiving auditory cues and stimuli, which can lead to disorientation, altered social interactions, and anxiety. Managing hearing loss through medications, environmental modifications, and training can help mitigate these effects.

Diseases that damage the brain, like encephalitis, brain tumors, and strokes, can also accelerate dogs' cognitive decline. Even when these conditions are treated, they often leave permanent damage that impairs memory, learning, and executive function. Kidney disease and resulting toxicity also link to cognitive dysfunction, likely because they impact blood flow to the brain. Controlling other health problems can potentially slow dementia progression.

Caring for a dog with CCD increases burdens on pet parents in various ways. They limit walks and activities to accommodate their dog’s reduced abilities. House soiling and other behaviours may require more diligent supervision. Pet parents can feel guilty leaving their disoriented dog home alone. While challenging, the loving bond remains and most pet parents deeply cherish the time left together.

Older pet owners tend to have more active dogs than younger ones. While counterintuitive, potential reasons for this include retirement giving older adults more time to exercise and interact with their dogs. Pet parent's age appears unrelated to the intensity of dog activity, suggesting these measures capture somewhat distinct aspects of physical activity.

It's important not to attribute all behavioural changes in senior dogs to pathology. With age, dogs may simply prefer more rest. Breed traits like retrieving may diminish. But their characteristic spark and lovable nature last a lifetime. Subtle changes are inevitable; dramatic shifts merit discussion with a vet. There’s no need to just “write things off” as old age.

This is a complex topic and any attempt to compress it into a digestible post may look like an oversimplification. If you want to go deeper, below you can find some papers that helped me write this post.