Puzzles

A rooster has 6, a cat and a dog have 3, so how many does a donkey have?

I think a donkey has four. A rooster has 5 letters (not 6), a cat (kot) has 3 letters, and a dog (pes) also has 3 letters. I can't think of anything else. Nothing about the appearance of these animals seems to fit the description. Most often, in such riddles, either the number of common letters in the words or the total number of letters in the words is compared.
p.s. Celt, answer this riddle already.