It's a great idea to have a breeding loan contract but without it being notarized and both parties signing, it's rather pointless unless for your comfort.

I know this because my friend loaned his sister a fair bit of money and had her sign a contract to pay him back and how much a month it was going to be. It was notarized and all but she never paid him back and there wasn't even much he could do. So while I wouldn't write up a contract personally but I would only do a breeding loan with a select few people that I trust.