Supplement use is common in Dog Aging Project participants, especially among dogs with orthopedic conditions, and varies by life stage.

Objective: To analyze the use of supplements reported by owners of dogs enrolled in the Dog Aging Project (DAP) to examine (1) the types of supplements being given to dogs within the DAP cohort and (2) the extent to which dogs diagnosed with specific conditions are being given supplements that are thought to improve those conditions. Methods: Supplement use, demographic variables, and owner-reported health conditions of interest were extracted from DAP survey responses collected from January 1, 2020, through December 31, 2022, from dog owners. Prevalence estimates were calculated in this cross-sectional design using survey responses from owner survey at enrollment. Free-text analysis of "other" responses was completed using Atlas.TI software to categorize additional responses. Results: Half of the dogs in this study (20,993 of 40,367 [52%]) received supplements. Of those receiving supplements, the most common supplements administered were omega-3 fatty acids (11,934 [57%]) and joint supplements (11,810 [56%]). Dog demographic characteristics were more strongly associated with differences in supplement use than owner demographic characteristics. Conclusions: Supplement use is common among dogs in the DAP cohort, with approximately half of owners reporting supplement administration. Given the frequency of their administration, veterinary professionals should discuss supplement use with dog owners. Clinical Relevance: Veterinary team professionals should consider spending more time discussing supplement use and efficacy with dog owners, especially for owners of senior pets.