In 1926, the Société Centrale Canine (SCC) decided that all dogs registered in the Livre des Origines (LOF) and born in the same year would be given a name beginning with the same letter, excluding the letter Z (not too many name choices in French).
Then in 1976, this practice was standardized for all animals and excludes the letters K, Q,W, X and Y, for the same reason as Z. You can add a nickname between the time an animal is identified with the S.C.C. and when he/she is given a birth certificate.
Pretty wild, yeah?
