Kasper appears 62 times at rank 1648 on male pets. It's the Scandinavian and German spelling of Casper, giving it a slightly sharper, more international feel than the standard English version. One of the three Magi in Christian tradition, and the friendly ghost of cartoon fame, Casper covers a lot of cultural ground in a single name.
The Ghost and the Magi
Casper the Friendly Ghost has been a children's media presence since the 1940s, making the name an intuitive fit for white or pale-colored animals. The Kasper spelling drops the soft "C" for a harder "K" that reads as more deliberately chosen and more European in origin. The human-name comparison is at /names/kasper.
Sound and Breed Fit
KAS-pur is two syllables, clear and slightly crisp. The harder opening consonant gives it more presence than the soft-C version. It suits white or silver-coated animals most naturally: Samoyeds, White Shepherds, and white cats of any breed. The Scandinavian spelling is also a natural fit for Nordic-origin breeds.
The Counter-Reading
The spelling choice between Kasper and Casper is mainly aesthetic: both will be pronounced identically, and vets will occasionally default to the more common spelling when typing. Owners who choose the K spelling do so because it looks different on paper, which is a valid reason. The name works either way.