My number one fantasy even though I know it would be extremely dangerous if it was even possible is to be seduced by a lover who then tricks me into being auctioned as a sex slave, my new owners take me to a horse stud farm and start my training as a belly rider, I'm kept in restraints in a stable while I am readied for my first riding lessons by being constantly stretched with increasingly larger dildos, unsure of my fate until i am strapped into a harness that is slung under a magnificent stallion, the mixture of fear and adrenaline as i'm positioned with my legs tied around his flanks spreading me wide open to accept the massive horse cock, swaying underneath feeling the enormous appendage slowly filling me completely, the adrenaline rush and realisation of what is happening blanking out my mind until i start to feel the pleasure as the stallion flares deep inside and he is led from the stables into the arena to the cheers of the gathered audience.
Advice from years ago was to find a smaller horse (pony) first who would 'adopt' me as I cared for him and experience the pony's interest in fitting his erection into me... an aide might be needed for safety (hubby, BF, stable owner). I met him fully clothed and began to brush and give him treats fully naked.
It takes time.
Let him know you as his naked caregiver who loves to wash his cock and lets him nuzzle your crotch... give it time.
A goal of being a belly rider will require similar trust of a larger horse, capable of having you hanging under him (not impossible I'm told).
After the pony has bred you, visit the larger horse of your choice and care for him --- the scent from your crotch will let him know you are a creature that he can also breed.
In the stable will be, at some point, a mare in season and her scent needs to be on you, just brush your naked hips against her to have the scent on you.
The larger horse now has a scent and a naked human mare in his stall, closed off to anyone trying to watch.
On a bale of hay or sturdy bench, lay on your back, have some apple slices or carrots for awards and open your knees so he can nuzzle and sniff and get a reward.
Guiding him is up to you or a helper, but he will fit and not push in deeper than you can take. It will be close to 10" or so, but you will feel him press hard as he fills you with warm cum, a wonderful feeling. (I had my husband to help guide him into me)
It's likely you will not cum the first few times (at least I did not) but patience pays off and his level of entry will be a little more subtle and you can move his rigid cock to fit your needs when the next times come along. I'm told they just need to know I will not avoid their approach to breed like a equine mare might do)
You now have a pony and a horse that are not afraid to approach you for sex. When naked, the approach will be fairly firm. Walking around in your jeans and shirt will have him lightly nudge you most of the time... give a treat and keep moving. It was stressed that I be naked for sexual play,
Belly Riding will be challenging to be secured under the horse without spooking him.
My first was with me in a harness of straps (like a cargo net) that needed a helper or two to clip into place without spooking the horse.... they led me in a small circle to get him used to me being under him for 5 or 6 times with an hour or so in between. I did not have hands tied around his withers nor my legs around his loin--- it would leave me without a way to get clear of him if he decided to move quickly.
With the pony breeding me first, I was sniffed all over by the horse as I lay in my harness of straps and as soon as he began to get interested, I was clipped into place and the semi hard cock placed at my pussy... He did not like that, and began to stomp, so I was lowered and lay on the hay bale for him to saunter over and then took care of his need. It felt wonderful that he was at ease and I was able to cum.
My husband and I decided it was a lot of risk for a fantasy event we had only heard about. I did not need to be the first Belly Rider to die trying to fulfill a fantasy.
There are photos and some film footage of women riding under a horse, fully clothed for a circus or rodeo event.... most seem like 50 year old pics and movies.
Having two large animals interested in making use of my availability is perfectly fine with us.