get it in writing and have a contigency plan in case they don't get you calves.
get some collateral as people in need don't take your needs into consideration.
i've lost a bundle from just such a person. semen, heifer, cash. they gave nothing except their word and got upset when i questioned it. the courts, brand inspectors won't help you fast enough if they don't come around. get your name on the brand, or a shared brand on the calves as the brand trumps a written contract, brand inspection without your brand on it without suing them. they can basically keep all of it till forced. when push comes to shove, those with the possession rather than the help lose out.