I was inspired by   JhonnyRebel 's piece "Ponygirls", and ended up writing a short story (now a novel!) on the topic. I've broken it up into short chapters (about 4400-6000 words), and will post more here as they are finished.
I still have a pool of ideas and scenes that I want to work through. That said, if you haven't seen my Journal on the Subject yet, go check that out. I'm looking for some more ideas, to see what sort of things you want to see in this story, what you like so far, any characters you want to see more of, background details you're curious about, all that sort of thing.

This story features a pair of bondage-loving anthro racehorses getting picked up on the side of the road by a generous stranger, and goes from there.
In this chapter, Sierra takes his horses out for a look at the stars, and reveals a bit about why he chose the names Lorianne and Azimuth for them.

Credit to   JhonnyRebel for the original image, which I used for the preview with a bit of cropping to make it square. Definitely go see the original Ponygirls piece! https://www.furaffinity.net/view/26041079/

Pasting the story below, with formatting, in case the doc is giving people problems or they just don't want to download it.

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There were a few things that Sierra had to get out of the way before he took his horses stargazing; the first order of business was to get the lights and bug repellent, both of which were essential with night falling. He had a pair of solar-charged lamps attached to his pack, and a headlamp tucked inside where it was easy to get to. The bug repellent was a small spray bottle, and Sierra misted it over himself, spraying a little extra on the backs of his hands so that he could rub it from there onto his face. He gave Azimuth and Lorianne a similar application, gently misting their rubber-clad bodies and then rubbing a little extra to their faces and into their manes and tails.
“There, that should keep the bugs and bloodsuckers away from you,” he said, adding “Bless you,” as Azimuth sneezed, followed not long after by Lorianne. “Hope this stuff doesn’t smell too bad for you,” he added, and both horses shook their head. “Good. Alright, stand up then,” he said, unhitching both anthros from the tree where he had tied their reins. They both stood up easily enough, for having blinders on and their arms tied wrist-to-elbow behind their backs. “We’re going over some uneven ground, like the trail we walked on the way up here. Do you need your arms for balance?” Sierra asked, and the mares both answered with a double stomp of their left hoof for no. “Alright then. Walk on,” Sierra said, and led the way to where the forest gave way to open fields of grass and wildflowers. From up here, Sierra could almost see to the city where he lived; the lights would be just a faint glow peeking above the horizon when the sun finished setting. That distant urban center was hardly worth looking for, not when the horizon was ablaze with the magenta, orange, and pink of sunset; beneath that shining splendor stretched mile after mile of rolling green forests, interspersed with the occasional road or river.
Sierra’s attention was pulled back from the scenery by a few muffled sounds from the horses. Both of them were turning their heads back and forth to try and get the best possible look at everything, when the presented scenery was far too big to fit in the narrow window their blinders afforded them.
“I completely forgot you had those on!” Sierra said, mentally slapping himself for the oversight. “Kneel—good girls,” he said as Azimuth and Lorianne both dropped to their left knees so that he could reach their heads and remove the blinders they had asked him to attach to their bridles. He noticed that the blinders weren’t just flaps of material—they had small electrical connectors in the snap fasteners that connected them to the bridle. The inner surfaces of the blinder flaps had a layer of clear material over the black synthetic leather. Some sort of head-mounted display? Maybe. Something to examine in a little more detail later. Sierra tucked the pieces into his pocket and cued the waiting horse girls to stand up. “So, now that you can see more of it—what do you think of the view?”
“Mmhmm!” Both horses said with an enthusiastic nod and stomp of their right hooves on the ground. Azimuth added a muffled “Mmhhk ‘oo” that Sierra interpreted as a ‘thank you’.
“Of course. I couldn’t just let the two of you miss the sunset,” he said, rubbing their backs and backsides, to a chorus of happy moans and muffled gasps. Sierra finished up with a pat, and then led the horses over to a good flat spot in the middle of the field. “Stay,” he said, letting go of their reins, and then unfurling the picnic blanket. “Here, both of you put one hoof on a corner, hold it in place,” he instructed, and they obliged, taking up places along one edge of the blanket, so that Sierra could more easily pull it out to its full dimensions with a minimum of wrinkles. With that done, Sierra took out his dinner dishes, which still had wash water sealed in the container. He opened that up and swung the bowl in a wide arc, splashing a fine mist of water and biodegradable soap across the field, then shook the bowl, lid, and spork dry as best he could. “That disperses the smell of food, so animals won’t come to investigate, and won’t find anything if they do,” he explained, taking a seat in the center of the blanket, and indicating for the horses to join him. They both knelt down, Azimuth on his right, Lorianne on his left, and nuzzled against him. “Good girls,” Sierra said, rubbing their manes and ears. “Go ahead and sit down all the way—we’re going to be here for a while watching the stars,” he said.
At this point, the last light of the sun had started to fade, and the sounds of birds with it. Crickets rose to fill the silence, along with the occasional sound of a night animal—the flutter and squeak of a bat overhead, or call of an owl, and the scurry of small animals returning to their dens for the night. The horses worked themselves from kneeling to fully sitting, which wasn’t an easy task with their arms bound, but they both managed it with a minimum of wobbling and near-falls. The two of them looked around in the gathering darkness, taking note of the tiny points of shimmering light starting to peek out above. As the last of the light slipped away, and everyone’s eyes adapted to the darkness, the scattered points of light turned into a blanket of twinkling dots, hundreds upon thousands of them all looking down on the earth below. Both horses gasped, trying to lean back or twist around to see more of the sky without falling over for the lack of support from their arms.
“Alright, I know you like the bondage, but it’s getting in the way of relaxing,” Sierra said. “So, hoof tap if you want your arms unbound.” There was a moment of hesitation as the two horses looked at each other to try and figure out what they should agree on. “Hey, it’s okay for you to pick something different than your twin, you know,” Sierra chuckled. Azimuth and Lorianne didn’t usually disagree like that, or at least they didn’t spend that long debating.
Azimuth blushed a little at the admonishment, and then tapped her right hoof on the ground, still clearly hesitant about it. Sierra gave her a warm and encouraging smile and disconnected the two binder sleeves from each other so she could lower her arms. With the stiff, thumbless mitts in place, Azimuth had no use of her fingers; it seemed like a good compromise to Sierra. He rubbed her arms gently to make sure the blood was flowing as it should be, and Azimuth sighed in pleasure, mumbling another “thank you, Master” into her gag. She wrapped him in her arms for just a moment, then pulled back. Her shyness read loud and clear, but her sweet and loving smile outshone that as it radiated around the rubber ball wedged in her mouth.
Sierra returned Azimuth’s smile, then turned his attention over to Lorianne. “So, do I free your arms as well? If you’re comfortable as is, that’s fine, I just need to know.”
“Mmmnh…” Lorianne said, still unsure. After a few more moments, she tapped her hoof on the ground for yes. Sierra nodded, and did for her as he had for Azimuth, complete with the gentle massage. Lorianne murmured her thanks, but didn’t hug Sierra, just fidgeted her mitted hands in her lap. After a few moments, whatever misgivings she had faded away, and she looked up at the stars, leaning back on her arms now that they were available to her again.
“Do either of you need or want your gags out?” Sierra asked. The response was quicker this time—both twins thumped their left hooves twice on the picnic blanket. “Okay then. Just making sure you’re both comfortable,” Sierra said, laying back and unrolling his datapad. The screen came on in night mode, meaning that it was tinted heavily towards the red end of the spectrum, with the brightness just barely on. “Hey Azimuth—you might like this,” he said, opening a star map on the pad. “People have been charting the stars in the sky for thousands of years, and they came up with a measurement system to measure the angle above the horizon. The horizon is zero degrees, and then you go up, ten, twenty, thirty degrees, all the way to the very top, ninety degrees. And that point, at the top of the sky is called…” He trailed off as the datapad’s screen showed him something he hadn’t expected. The stars all lined up just fine, but the label next to the pinnacle of the sky wasn’t the one he had expected.
“Mmmhmmr?” Azimuth asked, looking up at the sky and then back at Sierra, inquisitive and a little worried at the dismay on his face.
“Oh, oh wow I feel dumb,” he said, laughing a little and dropping one hand from the datapad down to rest on his face. “I’m okay, you don’t have to look so worried. It’s just that—I got mixed up. The 90-degree point is called the zenith, but I thought it was called the azimuth.”
Azimuth’s eyes widened at that, as she realized the connection Sierra had attempted to draw when he named her, taking Azimuth’s boring old serial number, #90, and renaming her after the highest point among the stars. On Sierra’s other side, Lorianne had perked up as well, interested at the origins of Azimuth’s name, and also curious if her own new name had a similarly lofty meaning. Azimuth tried to say something past her gag, but then fell silent again and nuzzled Sierra in thanks, her gaze meeting his only in short flashes before she looked away again, blushing.
He reached up a hand, gently catching the chinstrap of her halter. Azimuth nickered at the contact, a little shiver of pleasure running through her whole body from the point of Sierra’s gentle control outwards. “If you want the gag out, I can easily do that for you, Azimuth,” he said, stroking her ears and mane with his free hand.
“Mmm…mmhm,” she agreed, tapping her right hoof once. Sierra obliged her, unfastening the contraption from the halter. Azimuth opened her mouth wide to let the rubber ball slip out, then champed and licked at the empty spot in her mouth to get used to the absence. “Master—thank you,” she said. “I didn’t realize how much my name meant…Even though you misremembered, that’s okay—thank you.”
“We can always change your name to Zenith, if you prefer,” he suggested. “I can’t believe I fumbled that, astronomy was one of my favorite subjects when I was a kid…”
“Um, what does—what does ‘azimuth’ actually mean?”
“It’s the angle between a celestial object and North or South,” Sierra explained, after a quick check on the datapad to refresh his memory “So, an azimuth of 90 degrees would correspond to due East, not straight up.”
“I guess—Zenith would make more sense then, for me,” Azimuth said, and drew in a big breath that she let out with a sigh so heavy it made her whole body sag under the load. “If you want to name me after the high point in the sky, I mean, and not—East.”
“Hey—we’ll stick with whatever name you prefer. If you like Zenith, we’ll switch to it; if you don’t like that, we’ll stick with Azimuth, or even some other name you like better,” Sierra said, lifting the emotional weight from Azimuth with his soothing words and gentle touch.
“I—I like the name Azimuth, Master,” she said, with the usual fidget that came with the unfamiliar experience of sharing her opinion and having someone else listen.
“Well, then that’s your name,” Sierra nodded. “My good horses deserve names they like. Lorianne, did you want your gag out?” He asked, turning to face her. She had waited in trained silence while Sierra talked with Azimuth, and now gently tapped her right hoof on the ground and leaned forwards so Sierra could free her mouth as well. “Sorry to keep you waiting,” he said, unbuckling the gag and then giving Lorianne an extra scratch behind the ears to make up for the delay in letting her speak whatever was on her mind.
“Tha, that’s alright, Master,” she said, after running her tongue once around her mouth as Azimuth had. “You…you didn’t have to listen to us at all…Thank you.” She blinked a small tear out of her eyes, then shook her head to clear the tiny droplet off her facial fur as it tickled its way down.
Sierra touched a fingertip to Lorianne’s face, tracing over the little wet mark. “I know the facility taught you both to just act like dumb horses, and never express your opinions,” he said, and both horses cringed and shuddered. Sierra took a gentle breath to steady himself, and then went on: “I’m not like that—I value what you two have to say. If you’re gagged at any point, and want it removed so you can speak, let me know. I promise I’ll never hurt you for asking that.”
“Thank you, Master,” both horses said, in near unison. Lorianne shuddered a little more, and a few more tears started the journey along her downturned face. She twitched, but couldn’t seem to lift her arms to try and deal with the tears as they trickled and tickled through the soft and sensitive facial fur.
Sierra wiped those tears away, hands exploring over the gentle terrain of Lorianne’s equine features. “Was there anything you wanted to talk to me about? Your name, or what it means, or anything at all? It’s okay, Lori, you don’t have to cry,” he said as she leaned against him, whole body shaking.
“I’m n-not cr-crying bec-c-cause I’m s-sad,” Lorianne gasped out in between jerky breaths. “Y-you’re s-s-so g-good to us, ma-Master…it alm-most h-hurts,” she said, and then whatever training had kept her arms clumsy and out of the way broke down, and she flung herself onto Sierra in a near-crushing embrace. “I thought the facility was a good life for us!” She wailed. “Even though they made us race and race and race until we dropped from exhaustion! Even though they beat us and never let us speak! Even though they only ever touched us with a whip or shock rod! I thought that was the best we could ever hope for, the best we deserved!”
Sierra pushed against Lorianne’s constricting arms and pulled his face out of the smooth rubber of her bodysuit enough that he could breathe. “Gently! Need air!” He gasped out.
Lorianne squeaked and dropped him like a brazier of hot coals. “Sorry Master! Sorry, sorry, sorry!” She cried.
“Lori, it’s okay, calm down!” Sierra said, spots popping in front of his eyes as he spoke up before he had gotten enough oxygen back in his lungs. He took a few more gasps, until his breathing settled out and his ribs didn’t feel concave. “I’m fine, and I’m not going to hurt you—just needed to breathe,” he said, managing a smile at her so she would know that he wasn’t mad. That gesture only half worked; Lorianne still looked terrified, but at least her ears weren’t laid flat back against her head. “As for the ways you and Azimuth were abused—there is absolutely no excuse for that,” Sierra said. “None. If I ever see any of the dzinkas that hurt you, I’ll probably punch them in the face at least twice.” He slapped one fist into his opposite palm, then took a few breaths to calm himself. “Okay, how about we resume that hug, gently this time,” he offered, holding his arms out to Lorianne.
She hesitated for a moment, and then folded him into a much gentler embrace, draping her head and neck over his shoulder. “I’m sorry I hurt you, Master…”
“It’s okay,” he said, reaching around to rub Lorianne’s back. “You’re a big, strong horse, this sort of thing happens. You needed the hug, you were too emotional to control your strength, it’s fine—no permanent damage done. Shhh, you’re okay. You’re a good horse.” Without looking up, Sierra felt and heard Azimuth shifting behind him, pawing at the picnic blanket. “Azzy, there’s room in this hug for one more.”
That was all the cue she needed, and Sierra found himself once again sandwiched between the two equines, which jumped the temperature up from cool evening all the way up to almost sweating.
The hug lasted a good few minutes as the night deepened and more stars peeked out overhead. Lorianne broke off first, extricating herself from her twin and Sierra and sitting back on the picnic blanket. Her smile shone almost brighter than the half-moon. Azimuth gave Sierra a loving nuzzle and kiss before she sat back, the mirror image of her twin.
“Master—is there any special meaning to my name?” Lorianne asked. “I mean, like how Azimuth is connected to the sky and the stars?”
Sierra chuckled. “There is actually a special meaning, it’s even connected to your old number—however, it would be a lot harder to explain than Azimuth’s,” he said. “See, I’m really into classic vids and entertainment. In one of my favorites, there was a really cool car called a DeLorean, and it could travel through time when moving 88 miles per hour. So, 88 made me think of that, and then DeLorean became—Lorianne. I’m terrible at coming up with names, if you want to change yours I totally understand.”
“No, I—I like Lorianne,” she said, smiling and blushing at him. “It’s a name based on something special to you—I couldn’t think of anything better than that.”
“Alright. I’ll make sure you have the chance to watch the vid with your namesake,” Sierra said, scratching behind Lorianne’s ears and under her chin. “That’ll have to wait until we get home in a few days, though—I could pull Back to the Future up on my pad, but the classics really need a full wallscreen to enjoy properly.” He lay back on the blanket, staring up at the sky overhead, and yawned. “Uahhhh. Are you two getting tired? It’s been a long day, and I think it’s getting close to bedtime—but we can stay out here and watch the stars a bit longer, if you want.”
“Sleep sounds like a good plan,” Azimuth said, nuzzling against Sierra’s shoulder. “It’s been a long few days for us too, Master.” She shivered a little. “And it’s getting chilly out here.”
Sierra nodded, rolling to his feet and taking the horses’ leads. “Tomorrow night, I’ll brew up enough hot cider for all of us. For now,
let’s head back to camp and bundle up.” Both horses nodded, coming up to one knee in case Sierra wanted to gag them or tie their arms back. He took out one of his solar lamps, turned it on to a steady red glow, and held it up for them to see. “I’ve got one light for each of you, plus my own headlamp,” he said. “Do you want your light hanging from your halter under your chin, or in your hand?”
“Chin,” both horses said. “I don’t think we can hold those lamps, Master,” Azimuth said, holding up her hands in their thumb-and-fingerless bondage mitts.
“Your gloves can be easily removed,” Sierra pointed out. “But, if you prefer the lights under your chins, that works too.” He hooked the clips of the lead ropes to the two lamps, leaving both horses with a light dangling under their chin and pointed towards the ground. “There you go. Have to make sure you can see at night—and I’m not going to bind your arms any more either, because I don’t want you falling.”
He cued them to stand up, and once the horses were off the picnic blanket, Sierra folded it up and slung it over his back, then turned on his headlamp and led the way back to the campsite. There were a few other patches of artificial light visible here and there across the mountain—a softly glowing tent here, moving flashlights there, the more distant lights of a remote-control drone doing some nighttime stunt flying. Sierra had the beam of his headlamp, and also the two softly swaying lights above and behind him to light the way forward.
“Okay, let me think about this,” Sierra said as he and the horses returned to their campsite. He led the way under the tarp stretched out over the heap of branches and leafy material; Azimuth and Lorianne had to drop down to all fours to follow him under the low-hanging tarp. “How about you two lay down there and let me know if you think that will be comfy enough to sleep on—if it’s not, we’ll toss the picnic blanket on top so the branches won’t poke you quite as much.”
They both nodded, and settled down on the simple bed, to a chorus of creaking branches. The wood was wet and supple, so none of it broke. “This will be just fine, Master,” Lorianne said once she had settled in.
“You’re sure that it’ll keep us warmer than just being on the ground?” Azimuth asked, shivering a little again.
“Well, the branches will help some—but this should help a lot,” Sierra said, unrolling the picnic blanket over both horses. “There you go. That should keep you snug and warm all night long.” He reached under both their chins, unhooking the leads and also the lamps. “Here, see if you can turn these off and back on with your mitts on,” he said, holding up the lamps with the power buttons toward Lorianne and Azimuth.
Azimuth was the first to get one arm out from under the warm blanket to try and turn the lamp off. Lorianne tried as well, and like her twin, proved unable to push the small buttons with the end of her mitt. “Sorry, Master—can’t do it,” Azimuth said after several attempts, and even getting her second hand involved to try and turn the lamp off.
“Well, I think you need to be able to turn the lights on, if you want them in the night,” Sierra said. “Whether that’s for a late night trip to the toilet, or because you heard something scary out there in the dark and want to be able to see a little better. So, the gloves have to come off for the night, unless you have any better ideas.”
“Oh, alright,” Azimuth said, holding her arms out to him so that he could remove the long and restrictive gloves.
“Good girl,” Sierra said, removing Azimuth’s arm bindings and then starting on Lorianne’s. “You okay, Lori?”
“I—yes, Master,” Lorianne said, but sighed as her hands were freed. “I just thought that you’d leave us tied up and secure for the night—you didn’t even hitch us in place,” she said, nodding to the lead ropes that Sierra had coiled up and set off to the side.
“Again, that’s so that you can take care of yourselves tonight,” Sierra said. “I don’t want you to be tied up and helpless, because then you either have to wake me up, or you’re stuck if there’s some freak emergency. I don’t expect there to be such an emergency, but I would much rather be safe than sorry. Does that make sense?”
“Yes Master,” Lorianne and Azimuth said together.
“Good girls. And tomorrow, while I’m awake, there will be plenty of time for me to dominate you and try out different ways of binding you up,” Sierra assured, which earned him a more enthusiastic “yes Master!” from both horses. He smiled and chuckled softly, reaching out to pet both horses’ heads. “Anything else tonight? I still need to get my tent and sleeping bag set up and everything…”
Azimuth cleared her throat with a soft whicker. “Well, Master—there’s room for you between us,” she suggested, and then immediately amended herself: “I mean, you don’t have to! You can do whatever you want! And I’m sure that your tent is more comfortable and better and…it was a silly suggestion, masters don’t sleep in horse stalls.” She fell silent and turned away from him, her ears tilted back a little in embarrassment.
“Hmm,” Sierra said, thinking it over. “Well, I thought that I’d give you two your own space tonight—a bit of privacy, room to move around, that blanket not having to cover so many people—but if you both want me to join you, I certainly can,” he said, which perked both horses up and got them looking at him.
“You—really, Master?” Azimuth asked. “You don’t mind? You even—want to?”
“I’m still a little worried that you’ll roll over and squish me,” he said, but smiled and winked as he said it. “But that doesn’t seem like a major problem.”
“We’ll be careful, Master!” Azimuth agreed, nodding.
“Lori? Any objections from you?” Sierra asked.
“No, Master! You’d be welcome with us tonight!” Lorianne said, every bit as eager as her twin.
“Or any night!” Azimuth added. “Sleep with us all you want!”
“Aheh, well,” Sierra said, blinking. He wasn’t sure if Azimuth had meant that in the sense of actual sleep or something far more vigorous. If the latter, Azimuth was going to be disappointed. Sierra had no intention of taking advantage of the horses in that way until they understood the relevant laws and gave their informed and meaningful consent. “I’ll get my sleeping mat and bag, then. And so we’re clear, it’s just going to be sleeping tonight, not sex or anything like that.”
“Yes Master,” the two horses nodded. If either was disappointed with that news, they didn’t show it.
Sierra ducked out from under the tarp and made his way over to his pack, which he had left leaned up against a tree. His sleeping bag and foam mat were quick and easy to retrieve, but it did give him a bit of time to sort out his thoughts about sharing a bed for the night with two amorous anthros in skintight outfits. He probably wouldn’t need the sleeping bag that much, with two equine furnaces pressed next to him, and the picnic blanket over top.
When he got back under the tarp, he found that the horses had cleared a space between them for him. Lorianne pulled the blanket to the side so that Sierra would have an easier time getting settled. “Thanks,” he said, unrolling his camp mat over the branches and then laying down on top of it, with Lorianne on one side and Azimuth on the other. He had guessed correctly—the sleeping bag was not going to be needed at all tonight. “Actually—hang on a sec. I just had an idea,” he said, rolling back to his feet and over to his pack, bringing it under the tarp. “There’s a bundle of spare clothes in here that will work as a pillow for one of you. The other gets my sleeping bag, the bundle will be perfect to rest your head on,” Sierra explained, digging out the bag of clothes and handing that to Lorianne, passing the rolled up sleeping bag to Azimuth. “There we go, perfect.”
“But what about you, Master? What are you going to put under your head?” Azimuth asked, after testing the sleeping bag as a head support and finding it just right.
“Easy enough,” he said, setting his pack in that spot, and then taking off his jacket to roll up and place on top to add a bit of padding to the pack with its hard frame and other gear inside. “Voilà, just like that.”
“Well—as long as you’re comfortable that way,” Azimuth said, scootching closer to Sierra now that he was all set for the night. Lorianne did the same on his other side, and unfurled the picnic blanket over the group. Both horses nuzzled against Sierra, breathing
his scent. They both relaxed tangibly next to him. “Goodnight, Master.”
“Goodnight, Azimuth. Goodnight, Lorianne. Sleep well,” Sierra said, trading his headlamp for a warm hat from the pack. He left the headlight where he could reach it quickly, should the need arise in the middle of the night. He pulled the hat down over his eyes, and drifted to sleep with the two horses cuddled up next to him.

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Got suggestions? Go check out my Journal on the Subject and note me or leave a comment!

This is a very early draft, and I would appreciate any and all feedback you have after reading. If you want to see more of my writing and works, check out my DeviantArt gallery, which tends to have general audiences content instead of mature pieces like this.

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Part 2
Part 3
Part 4
Part 5
Part 6
Part 7
Master List of Chapters
Cast Page, Chapters 1-26