In dog, horse, and cow populations there are several blood groups, but as far as anyone knows cats have only one blood group system — the AB system, consisting of three types:  A, B, and AB.  A is dominant, but its prevalence varies by breed (a table in the second article breaks it down).  And by geography:  American cats are overwhelmingly type A.  That’s a good thing for cats facing surgery, because unlike dogs and horses, cats have no universal donor.  Despite the preponderance of this one blood type, cats are more diverse than dogs — we just haven’t been doing their matchmaking for that long.