Inubaka: Crazy for Dogs (いぬばか Inubaka) literally meaning 'Dog Idiot', is a Japanese manga series written and illustrated by Yukiya Sakuragi.
Sheltered and controlled by her parents for most of her life, and owner of a loyal mutt named Lupin, 18 year old Suguri wants to move from the country-side to the big city, Tokyo, to find a career and a new life. After being kidnapped and stranded at a rest area, Lupin mates another dog while her owner Teppei is not looking, shattering his dream of a litter of purebred puppies. To make up for her mongrel's wayward wooing, Suguri accepts Teppei's offer to work at the pet store he manages which leads her to numerous adventures of canine antics.
Original Run: 2004-2010
There's also a movie: