My #1 favorite book with an animal as the main character is J.R. Ackerley's book My Dog Tulip.
Quote Originally Posted by Amazon.com
My Dog Tulip is the ultimate bitch session--in the canine sense of the phrase, of course. In 1947, J.R. Ackerley rescued an 18-month-old German shepherd, and from the start her every look and move were to undo him. "Tulip never let me down. She is nothing if not consistent. She knows where to draw the line, and it is always in the same place, a circle around us both. Indeed, she is a good girl, but--and this is the point--she would not care for it to be generally known." As he anatomizes her from head to toe with the awe-struck precision of a medieval courtier, Ackerley instantly turns us into Tulipomanes. Alas, many of the mere mortals she encounters feel differently, for there are indeed two Tulips. One is highly strung but heroic, flirtatious but true. The other is a four-legged rejoinder to authority: a biter, a barker, and a dab hand at defecating her way around London. Not that any of these are her fault. "You're the trouble," Tulip's one good vet tells Ackerley as she banishes him from the surgery. "She's in love with you, that's obvious. And so life's full of worries for her."
Just a warning, Ackerley is, by today's standards, a very irresponsible dog owner. There is a purposeful mixed breed litter and he refuses to spay her, but for some reason I still love the book.