1) This is the Chihuahua (1959) by Maxwell Riddle, published by TFH Publications and distributed in petshops during the 1950s. The rare dustwrapper is shown on the first edition; TFH reprinted it with color-printed cloth and no dustwrapper.
2) Chihuahuas (2009) by Amy Fernandez, spiral-bound book that comes with a dvd, in the Barron's Educational Series.
3) Chihuahua Manual!: Insider's Guide to a Happy, Healthy & Well Behaved Chihuahua (2008) by Sandra Dean. What's a chihuahua "insider"? It's nothing. Generic self-published pseudo-book (i.e., an audio e-book).
4) The Chihuahua Report (2008) spiral-bound self-published book by Sandra Dean, who has used the web to advertise herself as an expert on the breed.