And don't forget the BVD test also. Super important not to spread diseases.
Be sure your cattle are up to date on all vaccinations prior to introducing the new bull. You might want to check and see what vaccination and worming the bull has had recently as well. He can easily bring in parasites that can wreak havoc on your herd.
I've loaned out bulls to friends and neighbours for the simple charge of looking after him well. They transport him, feed him and bring him back in one piece and ready to go and I'm fine.. Not real high end dollar bulls, but definitely in the several thousands and decently papered.
I've been lucky though, and if anything were to ever happen to the bull I'm just not sure how it would fair out on settling up. So that's one thing that needs to be agreed upon up front. Who's covering injury and death. If he breaks a leg, his pecker, or keels over dead.. Are you paying full price for a replacement, and if so what price is that.
Don't word of mouth and hand shake this.
Write up a contract and have both parties sign it. These days are different than the olden days when a hand shake was all you needed.
If you can't afford to replace the market value of the bull don't borrow him. As said above if he gets hurt or dies while with you that's on you. It's unfortunate we live in a day and age like this but it is what it is.
And never assume "He's a good guy. If something happens we'd work it out."