Your cock felt harder than it ever had before as the scent of the mare's heat kept bombarding your mind. You couldn't resist it anymore as you let the horse mind take over long enough to mate with Jessie. Jessie looked back at you pleadingly, but you didn't care anymore as you mounted the mare.
She let out a whinny as you pressed the tip of your cock against her vagina's entrance. You thrusted into her and she cried out as you pulled out a little and thrusted in again, the pure animalistic lust was overwhelming as the two of you mated, the sound of wet fur rubbing against wet fur hit your ears as you pounded into her.
Jessie's protests started to fade as you thrusted faster and harder into her as she whinnied louder. Your human mind tried to say this was wrong to try and stop the mating, but your horse mind was just too strong to give up the mating, and in a weird way it almost felt, fun and pleasurable.
Jessie neighed loudly as her vagina clamped down on your cock. You neighed loudly as you both came at the same time, your cum spurting into the mare's waiting vagina as you neighed in return as you bit down on the mare's shoulder.
You two just stayed there for a moment before pulling out of the mare and falling back onto all fours. She nuzzled you gently as your massive cock retreated back into its sheath and your human mind re-asserted itself finally. You couldn't believe you had just done that... and at the same time the idea of doing it again almost excited you.
"Well done my handsome Stallion," the attendant said as she stroked your mane. "You're both finished now and you'll have plenty more mares to mate with in the future. Jessie here is, a bit of a troublemaker, so she'll be sent off to a breeding farm now that her human mind is gone completely. A shame really, she was so beautiful, she was..."