I am attracted to the idea of exploring psychological disabilities in animals. In order for your claim to be seriously considered by the scientific community, however, I feel that a significant degree of expansion is needed in regard to the mental impairments you believe dogs suffer from as a result of ADHD. The DSM-5 diagnostic criteria is very clear in its definition that ADHD is defined by both hyperactivity AND inattention. I feel like this article specifically addressed the hyperactive behavioral tendencies of certain dogs, and neglected to address ways in which dogs display significant mental impairment. For future exploration of this concept, you could look in to studies where dogs are being trained to sit in fMRI machines. Such scans could be used to explore the temporal lobe activation of dogs said to have ADHD.