Aug 12, 2023

Longevity for dogs: how age-related diseases manifest across their lifespan?

An overview of veterinary studies looking at mortality, morbidities and patters of disease across dogs' lifespan

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.

Density plots of pathophysiological process (A) and organ system (B) causes of death with age

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.

This post is part of my deep dive into the topic of longevity for dogs to understand how can we help our best friends live longer and healthier lives. 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.

Puppyhood

Adolescence

Adulthood

Senior

Geriatric

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