The one ive adapted, i think originates from the BHS website, they do have one you can download i think, but not sure if you have to pay or something.
Basically list that the loanee is responsibly for all vets feeds insurance etc...what ponies suitable for, whats not to be done, how much notice should be given to end the loan, all it came with and that it is to be returned with those or the equivalents...