You should really give the passport to the loaner.
At the end of the day, if they were fraudsters and didn't have the passport there is nothing stopping them just changing his name and buying him another passport anyway.
What I did was make sure loanee signed contract stating that she is in no way what so ever owner of horse, and got a pic of her and horse so that I could say it was deffo her that signed it etc. Not that I didn't trust her.
Lol, soz but I just though - u know those weight loss before pics when folk hold up a newspaper? U could get them to hold horse, and news paper and a sign that reads - I do not own this horse.
I gave the original of the passport to the loanee like others along with vaccination certificate. Kept photocopies for myself and also attached them to the copies of the loan agreement. I kept the Farmkey freezebranding certificate that he has for loss of use and the Identichip paperwork as I figured she wouldn't need them unless he disappeared