Feeding by life stage: what dogs need as puppies, adults and seniors

Nutritional requirements change substantially across a dog's lifespan. Feeding a puppy food to a senior dog, or keeping an adult on puppy food after maturity, can cause real harm — excessive calcium in a large-breed puppy, excess calories in a sedentary senior, or insufficient protein in a senior dog whose muscle-maintenance requirements are actually higher per kilogram than a middle-aged adult.

The AAFCO life-stage framework defines three feeding categories: growth (puppies and pregnant/lactating females), maintenance (adult dogs), and all life stages. WSAVA and AAHA add nuance for large breeds, geriatric dogs, and therapeutic diets. Here is what that means in practice.

The puppy stage: growth (weaning to maturity)

Puppies have 50–75% higher energy requirements per kilogram of body weight than adult dogs. They need more protein (for muscle and organ development), more calcium and phosphorus (for skeletal growth), and more DHA (an omega-3 fatty acid from fish oil) for brain and eye development. Puppy foods labelled "for growth" or "all life stages" are formulated to meet these elevated requirements.

• Small breeds (under 10 kg adult): reach maturity at 9–12 months; transition to adult food then
• Medium breeds (10–25 kg): mature at 12–15 months
• Large breeds (25–45 kg): mature at 15–18 months; use large-breed puppy food throughout growth
• Giant breeds (over 45 kg): may not fully mature until 18–24 months; use giant-breed puppy food

The adult stage: maintenance (maturity to approximately 7 years)

Once a dog reaches physical maturity, their primary nutritional goal is maintenance — sustaining lean body mass, organ function, skin and coat condition, and energy balance. Adult maintenance foods have lower energy density and calcium levels than growth formulas.

The exact nutrient profile an adult dog needs varies by body size, activity level, and whether they are intact or desexed. Desexed dogs have approximately 20–30% lower caloric needs than intact dogs of the same size and activity level, according to research published in PLOS ONE (Bermingham et al., 2014). Overfeeding a desexed adult is one of the most common causes of canine obesity.

The senior stage: what actually changes after 7 years

The traditional threshold for "senior" is 7 years, though giant breeds age faster (senior at 5–6 years) and small breeds age more slowly (senior at 8–10 years). The nutritional changes at senior status are more nuanced than marketing implies.

• Protein: older dogs actually need MORE high-quality, digestible protein per kilogram to maintain muscle mass, not less — the old idea of protein restriction for kidney disease is now reserved for dogs with diagnosed kidney disease, not as a general preventive measure (WSAVA)
• Calories: many sedentary seniors need fewer calories overall, but some older dogs lose weight easily and need more — monitor BCS monthly
• Phosphorus: restriction is appropriate for dogs with diagnosed chronic kidney disease (CKD); not for healthy seniors
• Joint support: some senior foods include added glucosamine and chondroitin; evidence for supplementation is mixed, but these additions are not harmful
• Fibre and digestibility: older guts are less efficient; highly digestible ingredients are beneficial

Transitioning between foods

Change foods gradually over 7–10 days to avoid gastrointestinal upset: mix 25% new food with 75% old for days 1–3; 50/50 for days 4–6; 75% new for days 7–9; 100% new on day 10. If soft stools or vomiting occur, slow down the transition. Puppies with immature guts are particularly sensitive to abrupt changes.