Quote:
A donkey will bond with a cow or a horse, or some such - but I have never heard of a donkey bonding with a chicken. 
However, donkeys will protect their own - and having more than one donkey doesn't mean they will tolerate a dog or a coyote or any predator in their pasture just because it happens to be by the chicken coop and not by them. My donkeys despise having any creature in their pasture that doesn't belong. 
so yeah, in theory for a guard donkey you want one - but in practice, I just wouldn't do it.  But that's just me. 
eta - if you get to know a donkey, your outlook might be different on the "lone donkey" thing. Not criticizing, or trying to make ya look dumb, just trying to say that after having donkeys, I've come to realize how sensitive they can be.  One of my donkeys was depressed for three weeks because we moved her from her old home and her old buddy she used to hang to with - this in spite of having three other donkeys from the same farm/pasture she came from, and spoiling her every chance we got.  She had it nice here, and had some old friends, but didn't have her best friend, who was a Jack and couldn't come along (we have two jacks already).  I would just feel like an old meany if I had just one donkey and no other donkey friend for it. 
meri