Large dogs appear to age at a faster rate than small dogs; the aim of the present study was to examine the effect of breed (short-lived vs longer-lived) and size (large vs small) on behavioral aging. Owners of purebred (n = 651) and mixed-breed (n = 153) dogs ≥8 years of age completed surveys evaluating cognition and behavior along several indices: ingestive, locomotory/arousal, memory/learning, and problem behaviors, as well as human–dog interactions. Binary logic regression analysis was conducted across longevity groups (short-lived, <11 years; medium-lived, 11–13 years; long-lived, >13 years), group size (small, <35 cm; medium, 35–55 cm; large, >55 cm), and breed (purebred vs mixed-breed). Significant differences were observed across groups in several behavioral parameters, but all significant differences in cognitive aging failed to show a trend across longevity, size, or breed. While breed longevity and size appeared to influence some aspects of aging (eg, cardiovascular and skeletal systems), the expected age, size, and breed effects with respect to behavioral aging were not shown. It was concluded that considerable variation in the behavioral aging process exists and various breed-related and environmental factors must also come into play.

Commentary
Astute clinicians should schedule longer appointments for patients >10 years of age to answer client questions and discuss the canine aging process. Knowledge of impending sensory deterioration (eg, deafness, blindness), especially in small dogs, can help owners recognize clinical signs so the environment can be modified to accommodate the disability.—Katherine A. Houpt, VMD, PhD DACVB

Source
The effect of breed on age-related changes in behavior and disease prevalence in cognitively normal older community dogs, Canis lupis familiaris. Salvin HE, McGreevy PD, Sachdev PS, Valenzuela MJ. J VET BEHAV 7:61-69, 2012.