
The breeder I would hope if you are the one paying for everything. This is why you need every eventuality covered by an agreement. For example suppose you no longer wanted to show, or wanted to have him castrated?
A friend of Friend had a bitch pup on terms. When the bitch grew up the owners really didn't want to breed from her, they didn't think she had a suitable temperament.
The breeder insisted she wanted her bred from, but the timing wasn't good for the owners, and she was charged a fee for putting it off for a year, and then had to breed a litter the next year from a bitch they thought shouldn't be bred from, and they had to bear the costs too.

So they basically had a bitch for free, then paid the equivalent of a pet puppy for delaying breeding and had to give over two pups, bad bargain for them.
Slightly different situation to a partnership, but similar problems could crop up if not ironed out before hand.
I also knew someone who bought a puppy from a breeder who had the bitch and litter in partnership with life partner, the joint breeders/owners parted company and the other owner wouldn't sign the paperwork for the pups and left the country and the lady had a pup she couldn't register in her name or show. don't know if it ever got sorted.