Common Dog Diseases: Early Signs Owners Miss

Five conditions account for most serious illness in adult and senior dogs: cancer, chronic kidney disease, heart disease, diabetes, and arthritis. Cats share several of them, with kidney disease and hyperthyroidism especially prominent.

Age is the strongest single risk factor. As dogs and cats age, organ function declines, immune defenses weaken, and the risk of chronic disease rises. Dogs typically enter their senior years between 7 and 10 years of age — earlier for large and giant breeds, later for small breeds. Cats generally begin showing age-related changes around 10 to 12. Senior pets face a cluster of related challenges: declining organ reserve, slower healing, and greater susceptibility to infection. Lifestyle, diet, genetics, and body condition from younger years all influence which conditions appear and how quickly they progress.

Regular health checkups — ideally every six months for senior pets — matter because many of these diseases produce no obvious symptoms in their early stages. Routine bloodwork, urinalysis, and imaging can detect problems well before anything is visible at home. A broader overview of routine monitoring is covered in the guide to senior pet care.

Not every change in an older pet is cause for alarm, but some shifts deserve a closer look. The useful distinctions are usually speed and severity: normal aging is gradual and mild, while disease tends to arrive faster or go further.

Keeping a simple written log turns vague impressions into information your veterinarian can use. Record:

• Lumps or swelling — note size, location, and whether it is growing.
• Wounds that do not heal within a normal timeframe.
• Unexplained weight loss — weigh your pet monthly and record the number.
• Changes in breathing — coughing, panting at rest, or open-mouth breathing (especially in cats).
• Appetite and energy shifts — eating less, refusing food, or marked lethargy.
• Unusual bleeding or discharge from any body opening.

Bring dates and descriptions to the appointment. A timeline helps a veterinarian distinguish a slow trend from a sudden event, and that distinction often changes the diagnostic plan. When in doubt, note the change and its timing and raise it at your next visit — or schedule one sooner if the change came on suddenly.

These three are among the leading causes of serious illness and death in senior pets.

Cancer. Roughly half of dogs over ten years old will develop some form of cancer. Common canine cancers include mast cell tumors (the most frequent skin tumor), lymphoma, osteosarcoma (especially in large breeds), and hemangiosarcoma (often affecting the spleen or heart). In cats, oral squamous cell carcinoma, lymphoma, and mammary tumors are most common. Unspayed females of both species face a significantly higher risk of mammary tumors. Early detection depends heavily on owner observation — new lumps, non-healing sores, unexplained weight loss — because many tumors are silent until they are large or have spread.

Chronic kidney disease (CKD). CKD affects an estimated 30–40 percent of cats over ten and a meaningful number of senior dogs. The kidneys filter waste, regulate fluid balance, and manage electrolytes — functions that erode gradually. Early CKD is often invisible at home; by the time symptoms appear (increased thirst, weight loss, vomiting, uremic breath), significant kidney function has already been lost. CKD cannot be cured, but dietary management, hydration support, phosphate binders, and blood-pressure control can slow progression and maintain quality of life for months to years. The staging system veterinarians use is explained in kidney disease stages.

Heart disease. Small-breed dogs are prone to degenerative mitral valve disease; large breeds more often develop dilated cardiomyopathy. In cats, hypertrophic cardiomyopathy is the most common form and can deteriorate suddenly without prior warning. Early cardiac symptoms are subtle — a soft cough at night, slightly reduced stamina — but untreated heart disease progresses to fluid buildup, breathing difficulty, and, in cats, the risk of aortic thromboembolism (sudden hind-leg paralysis). Labored breathing, open-mouth breathing in a cat, or collapse is an emergency; go to a veterinarian immediately rather than waiting for an appointment.

Diabetes is one of the more common dog diseases in the metabolic category, and it presents differently across species. In cats, diabetes resembles human type 2 diabetes (insulin resistance); in dogs, it is closer to type 1 (insufficient insulin production). Obesity is a significant risk factor for both.

The classic signs — increased thirst, increased urination, increased appetite, and weight loss — are sometimes called the "three polys plus weight loss." Other clues include a dull coat, hind-leg weakness (diabetic neuropathy, more common in cats), and recurrent urinary tract infections. Left untreated, diabetes can progress to diabetic ketoacidosis, a life-threatening emergency.

Management typically involves insulin injections, which owners learn to give at home, along with dietary changes — high-protein, low-carbohydrate food is usually recommended. Some cats achieve diabetic remission with early, aggressive treatment and strict diet control. Dogs generally require lifelong insulin.

Senior pets may also develop other endocrine conditions: hyperthyroidism (very common in older cats) and hypothyroidism (more common in dogs). Both are diagnosed with blood tests and managed with medication or, in the case of feline hyperthyroidism, radioactive iodine treatment or surgery.

Changes in drinking, urination, and weight are the shared thread running through all of these:

• Drinking noticeably more water than usual — especially if you are refilling the bowl more often or finding it empty.
• Urinating more frequently or in larger volumes — or having accidents indoors despite being housetrained.
• Losing weight despite eating the same amount or more — a hallmark of diabetes, hyperthyroidism, and some cancers.
• Gaining weight without dietary change — may point to hypothyroidism or fluid retention from heart or kidney disease.

Any persistent change in thirst, urination, or weight warrants a vet visit and baseline bloodwork.

Osteoarthritis is one of the most widespread sources of chronic pain in senior pets, and one of the most consistently underdiagnosed. In cats, roughly 40 percent show clinical signs of osteoarthritis, and about 90 percent of cats over twelve have radiographic evidence of joint degeneration. Diagnosed rates in dogs look far lower — UK primary-care records put the annual period prevalence of diagnosed appendicular osteoarthritis at about 2.5 percent of dogs — but that gap reflects how seldom the disease is recognized and recorded in practice, not how seldom it occurs. Because pets instinctively hide pain, many cases go unrecognized until the disease is advanced.

Signs in dogs: difficulty rising, stiffness after rest, limping, reluctance to climb stairs or jump into the car, and sensitivity when certain joints are touched.

Signs in cats: reduced jumping height, no longer grooming hard-to-reach areas, increased sleeping, and general withdrawal from activity. Owners frequently attribute these changes to "just getting old" rather than recognizing chronic pain. The guide to recognizing pain in senior pets covers the subtler behavioral signals in more depth.

Arthritis management combines several approaches:

• Weight control — even modest weight loss reduces joint stress significantly.
• Medication — NSAIDs, joint supplements (glucosamine, chondroitin), and neuropathic pain drugs as prescribed by a veterinarian.
• Physical therapy — hydrotherapy, passive range-of-motion exercises, and acupuncture.
• Home modifications — soft orthopedic bedding, ramps instead of stairs, non-slip mats on hard floors, and raised food bowls.

A gradual slowdown over months may be normal aging. Schedule a veterinary evaluation if you notice a sudden change (your dog stops climbing stairs overnight or can no longer jump onto the couch), limping that lasts more than a day or two, reluctance to be touched in specific areas, whimpering or changes in posture such as a hunched back, or reduced activity combined with appetite loss, weight change, or altered breathing. Early intervention — adjusting medication, starting physical therapy, or modifying the home environment — can restore comfort and slow further decline.

Disclaimer: This article is for informational purposes only and does not replace professional veterinary advice. If your pet is experiencing health issues, consult a licensed veterinarian.

1. Senior Dog Care — VCA Animal Hospitals
2. AAHA Life Stage Canine Guidelines
3. Senior Pet Care FAQ — AVMA
4. Prevalence, duration and risk factors for appendicular osteoarthritis in a UK dog population under primary veterinary care — NIH/PMC
5. Diagnosis and Management of Feline Osteoarthritis — Today's Veterinary Practice