A racehorse at stud!
Why? Why bloody not
Cos they grab your dick and stick it in a huge rubber johnny just as you are about to jizz up... 
I saw it on the telly once... the mares just get the turkey baster treatment...
Well put BM. Are you available for doing the narration on any of these documentaries? 
"And JOM is coming on strong .... he's neck and neck with the mare ......... and, oh dear, he's been pulled out again by Big Willy, his trainer, who is holding on for grim death ~ what a disappointment for JOM who looked as if he had it in the bag ..................... again"
