Comparative locomotor costs of domestic dogs reveal energetic economy of wolf-like breeds.

The broad diversity in morphology and geographic distribution of the 35 free-ranging members of the family Canidae is only rivaled by that of the domesticated dog, Canis lupus familiaris. Considered to be among nature's most elite endurance athletes, both domestic and wild canids provide a unique opportunity to examine the variability in mammalian aerobic exercise performance and energy expenditure. To determine the potential effects of domestication and selective breeding on locomotor gait and economy in canids, we measured the kinematics and mass-specific metabolism of three large (>20 kg) dog breed groups (northern breeds, retrievers and hounds) of varying morphological and genomic relatedness to their shared progenitor, the gray wolf. By measuring all individuals moving in preferred steady-state gaits along a level transect and on a treadmill, we found distinct biomechanical, kinematic and energetic patterns for each breed group. While all groups exhibited reduced total cost of transport (COT) at faster speeds, the total COT and net COT during trotting and galloping were significantly lower for northern breed dogs (3.0 and 2.1 J kg-1 m-1, respectively) relative to hound (4.2 and 3.4 J kg-1 m-1, respectively) and retriever dogs (3.8 and 3.0 J kg-1 m-1, respectively) of comparable mass. Similarly, northern breeds expended less energy per stride (3.5 J kg-1 stride-1) than hounds or retrievers (5.0 and 4.0 J kg-1 stride-1, respectively). These results suggest that, in addition to their close genetic and morphological ties to gray wolves, northern breed dogs have retained highly cursorial kinematic and physiological traits that promote economical movement across the landscape.