Why do dogs' nutritional needs vary according to their size?
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A small dog has energy requirements per kilogram of body weight that are much higher than a large dog, because its skin surface is proportionally greater relative to its mass: it therefore loses more heat and must compensate with a faster metabolism.
The surface-to-mass ratio in practice
As an animal becomes smaller, its body surface decreases more slowly than its volume (and therefore its mass). A 1.5 kg Chihuahua thus has, relative to its weight, a much larger heat-exchange surface than a 60 kg German Shepherd. This constant heat loss forces the small dog's body to maintain a higher basal metabolism per kilogram, resulting in energy requirements that can be two to three times higher, per kilogram of body weight, than those of a very large breed.
In puppies of large and giant breeds, the problem reverses: their growth is prolonged (up to 18–24 months) and their skeleton develops very quickly in size. An excess of energy or calcium during this period speeds up growth that is already rapid, without the bone structure having time to solidify, promoting musculoskeletal disorders such as hip dysplasia or osteochondrosis. Strict control of calorie and mineral intake, tailored to the intended adult size, is therefore essential during this phase; a veterinarian's advice allows this follow-up to be adjusted.
Size, metabolism and lifespan: a paradox
This link between size and metabolism is accompanied by an inverse phenomenon for lifespan: small breeds, with their faster metabolism, generally live longer (12 to 16 years on average) than large breeds (8 to 10 years), whose rapid growth and large mass accelerate cellular aging. This extreme variability in body size, unique among domestic species, explains why dogs' nutritional recommendations are always based on adult size and growth stage, rather than following a single rule applicable to all dogs.
