How exercise changes a pet's calorie and protein needs

Two dogs of the same weight can need very different amounts of food. A neutered pet dog that walks twice a day sits near the standard maintenance estimate, a detection dog on a working schedule needs somewhat more, and a sled dog in a long race burns far more. Any formula is only a starting point. The dog's body condition over the following weeks shows whether the estimate was right.

Estimating daily calories

Veterinary energy estimates start with the resting energy requirement (RER), the energy used at rest in a comfortable environment. The standard formula is RER in kcal per day = 70 × (body weight in kg)^0.75. A 20 kg dog has an RER of about 660 kcal.

Daily needs are then estimated by multiplying RER by a factor for life stage and neuter status. The Merck Veterinary Manual uses these factors for healthy adults and notes that any calculation may need to change depending on how the animal responds:

Those factors describe ordinary pets. Working dogs can sit a little higher. Twenty odor, explosive and human detection dogs that held a steady weight for six months ate about twice their calculated RER, which the authors judged similar to an older standard maintenance figure for dogs, and the number of searches a dog performed was only weakly linked with its energy needs. Endurance sled dogs during multi-day races are the far end of the range, with energy use many times that of a pet.

Feeding guides on bags usually offer one line for "active" dogs and one for the rest. Treat the bag figure and the formula the same way: feed the estimate, then weigh the dog and check its ribs and waist every few weeks and adjust.

Protein for hard-working dogs

The Merck Veterinary Manual gives the minimum protein for adult dog food as 18% of dry matter, and 26% for adult cat food. Those minimums are set for maintenance, not for dogs in heavy training.

Much of the research on protein and exercise in dogs comes from sled dogs. In a study of 32 Alaskan sled dogs given diets with 18%, 23%, 29% or 35% of their energy from protein through 12 weeks of hard training, the dogs on 18% lost aerobic capacity and had more soft tissue injuries than dogs on the higher-protein diets. The authors concluded that 18% of energy from protein was not enough for sled dogs in training. Note that these figures are percentages of calories, which is not the same as the protein percentage printed on a bag.

Those results do not translate directly to a pet dog that walks, runs with its owner at weekends or does an agility class. A complete adult food with an adequate protein level, fed in enough quantity to hold body condition, covers most of these dogs. Cats already need a high-protein diet, and an active cat generally needs more of its usual food rather than a different formula.

Fat, carbohydrate and fuel

Fat supplies more than twice the calories per gram of protein or carbohydrate, which is why sport and working dog foods are richer in fat: they pack enough energy into a meal the dog can comfortably eat.

What the dog burns while running is less settled than the old "fat for endurance, carbohydrate for sprinting" rule suggests. A 2021 review of research on racing sled dogs argues that conditioned sled dogs rely on glucose as their main fuel during sustained exercise, even when most of their dietary energy comes from fat, and says how they keep glucose supplied is still being studied. Sprinting does not clearly favor carbohydrate either. When seven racing Greyhounds were switched between two diets, they ran faster on the higher fat and protein, lower carbohydrate diet. The difference was small, about a quarter of a second over 500 m, and the opposite of what the carbohydrate-for-sprinting rule predicts.

Water in warm weather

Merck puts the water requirement of most mammals at roughly 44 to 66 mL per kg of body weight a day in a comfortable environment, so a 20 kg dog at rest needs roughly 0.9 to 1.3 liters from food and drink combined. Exercise and heat push that up, because dogs shed heat mainly by panting, which costs water.

• Carry water on long walks and runs and offer it at regular breaks, before the dog is visibly flagging.
• Move exercise to cooler parts of the day in hot weather.
• Stop and cool a dog that pants heavily, stumbles, drools thickly or lies down and will not continue. These are warning signs of heat stress, and a dog that does not recover quickly needs a vet.

Electrolyte supplements are sometimes used for dogs working long hours in heat. For ordinary pet exercise the evidence is limited, and a complete diet already supplies sodium and potassium.

Timing meals around exercise

Many owners of large, deep-chested dogs are told not to exercise them soon after a meal because of gastric dilatation-volvulus (bloat). The evidence behind that specific rule is thin. A Dutch case-control study in Great Danes looked at the interval between feeding and exercise, the length of exercise and overall activity, and did not identify any of them as a risk factor; age and small food particle size were. That was one breed and a modest number of cases, so caution still makes sense:

• Before hard exercise: feed the main meal well beforehand, or after the session, rather than immediately before. Many dogs are uncomfortable running on a full stomach.
• During long outings: dogs out for several hours can have small snacks and water at breaks.
• After exercise: let the dog settle and stop panting before its meal, and offer water without letting it gulp a huge volume at once.

Signs of bloat include a swollen or tight belly, retching without bringing anything up, restlessness and drooling. It is an emergency at any time of day, whatever the dog last ate.

Adjusting through the year

Activity rarely stays constant. Heat waves, icy pavements, holidays, an injury or a new job can cut a dog's exercise for weeks, and the portion that suited a busy month will then add weight. Feed for the exercise the dog is actually getting. A Husky that lives on a sofa does not need sled-dog rations, and a Labrador walked around town does not need a working retriever's portion. When exercise drops, trim portions a little and check body condition again, rather than waiting for the scale to show a large change.

Sources

1. Nutritional Requirements of Small Animals. Merck Veterinary Manual.
2. Maintenance energy requirements of odor detection, explosive detection and human detection working dogs. PeerJ, 2015.
3. Effect of protein intake during training on biochemical and performance variables in sled dogs. American Journal of Veterinary Research, 1999.
4. Glucocentric Metabolism in Ultra-Endurance Sled Dogs. Integrative and Comparative Biology, 2021.
5. Maintenance energy requirements and the effect of diet on performance of racing Greyhounds. American Journal of Veterinary Research, 2000.
6. Small size of food particles and age as risk factors for gastric dilatation volvulus in great danes. The Veterinary Record, 1998.