You stepped through one of the fancy doors that led out of the garden. The interior of the castle was warmer. It also smelled nice, but the garden hadn't smelled bad either. Just two different, nice, scents. Both floral. The one inside seemed subtler.

A pony in gleaming armor marched past, though his eyes did dart towards you, sizing you up as he went by.

You raised a hand in greeting, but he just nodded in kind and kept right on walking. At least he didn't seem upset at you being there. That was good, right?

You moved in the direction Luna had pointed you, feet making the quietest sound on the smooth floor, basically silent. It was quite a stark difference from the clip-clop you could hear from other ponies moving around. Their hooves were not meant for stealth. You practically felt like a ninja in comparison.

At least until you felt your furry junk being handled, which was extra odd since you were the only one around with hands, you thought? You jumped back in surprise to see a glimmering field follow along with you. A unicorn proved to be the source, her horn glowing the same shade. "A new stud? You look fresh off the boat, as they say."

You didn't like the way she was eyeing you, to say nothing of the inappropriate horn magic on your goods. Feeling bold, you stepped towards her instead of away. Her expression relaxed. "Want to play a little? That's a good little stud."

You didn't. With a flick of a finger, you thwipped her across the horn and the glow died away as she jumped in surprise. "Why! I never!" She stormed off, tail swaying behind her, held high. You got the impression it was more to show disgust than to invite further playing.

With her defeated, you had little trouble following the small signs at intersections to locate the lab.

The carpet went away as you went down the last hall, leaving your feet to tread on the cool and smooth marble floor. The walls turned yellow in color as you approached the final door.

Two guards stood in front of it. One of them was female, which was a surprise. Weren't all guards male?

Both nodded towards you. The female gestured back with a toss of her head. "This area is off-limits to studs unless specifically called for, stud." She didn't sound angry, as if just reciting a fact.

That was alright. You were invited to come by Luna.

The male nodded. "If she said so specifically. You may be a stud, but even you are beholden to the laws of the land. We will confirm your story later." He stepped to the side. "Welcome to the fertility clinic." He paused a split second. "I'm not trying to be gruff, Stud." An ear perked. "Do you have a name?"

You did, and you shared it.

The female smiled faintly. "Better than Stud, that's for sure. Please, enter with caution. Look, don't touch, unless directly instructed."

Did they have any clothing, for lab safety?

The male's horn glowed, pulling open a small side closet and retrieving a full set of pony clothes. Gratefully you took the pants from his magic and slipped them on. They weren't a precise fit at all, but you're not dangling in the breeze anymore. Feeling brave, you took the front and tried it on. It seemed that pony forelegs were just as free-moving as human arms, so they didn't fit nearly as poorly as one might think.

You were dressed! You were dressed like a scientist, sure, but dressed! You asked if it would be a problem if you kept them.

The female shook her head. "If you need clothes, we'll send somepony by your quarters to size you. Until you get a new set, keep those, but have them returned after."

Things were looking up!

The one flaw? The pants had a hole for a tail that you didn't have. Oh well.

You proceeded past the two with a friendly goodbye shared.

The area just past the door was a form of airlock. The room glowed red as some kind of disinfectant(?) hissed into the place for a moment before the red faded and you could proceed forward.

A scientist mare, dressed much like you were, with some glasses in addition and goggles over the glasses, looked up at you as you came in. "A new stud?! I wasn't told you were coming. Is there an experiment planned? Why are you dressed like that?" She was full of questions and looked a bit harried.

You explained that Luna had invited you there to look around and maybe lend a fresh perspective.

"Oh! Oh... I suppose that's alright." She turned from you. You saw even her tail was covered protectively. "I'm Careful Study, nice to meet you..." You provided your name. "Ah, charming. This way, I'll give you a little tour."

She began to lead the way, showing off what seemed to be fairly standard sciency rooms, just with 40% more crystals involved. "Since the great sterilization, we have been tasked with finding a way to restore the species' vitality. We hope to either get males up to the level required to fertilize mares, or lower the mare requirement down to what males typically produce." She glanced over her shoulder. "You probably heard that males are sterile. This is not entirely accurate. They do produce male energy and seed, just woefully insufficient amounts compared to the staggering quantities a mare requires."

That sounded bad, but if they weren't completely sterile, why couldn't they work with that?

She arced a brow. "I've been informed that the worlds the princesses usually plunder for studs are typically ignorant in the ways of magic." She turned to face you. "The instant a stallion releases into a mare, what happens?"

You blinked a little. Was this a biology quiz? You explained how sperm works, basically. One lucky dog entered an egg, they combined and a new little could-be person was formed. Ta da! Miracle of life.

She nodded slowly. "That's a start, but you're missing the other half, the magic half. And it's grown more... complex for ponies." Her rump settled on the ground as she heaved a weary sigh. "To start, female eggs have far less of the living script than they should, and require not just one male seed, but many, all in the precise missing fashions to create a whole set of instructions. For the average stallion, they just can't hack it. They give out their sprinkling of seeds, but..." She wobbled a hoof. "Some of them are matches and get in, but not enough. You have an egg without a completed set, and no pony is made."

Species-wide genetic damage? That was pretty severe... But what was that about the magic half?

She nodded at you as her horn began to glow. "I'm certain I'm not the first unicorn you've seen." You assured her she wasn't. "We ponies are inherently a magic species. Though unicorns show it most obviously, we all do. When a male releases seed, he also releases a very specific biological spell. He basically casts a foal making spell. It instructs the female's body to be ready to catch the fertilized egg, care for it, and make a healthy pony or two out of it. It's all very wonderful, and worked fine, until the great sterilization." She let out a weary noise. "Now the spell is too weak to send the signal. We've had some, limited, success having a unicorn throw the spell at just the right moment precisely as a mare is being fertilized, but that's far from ideal." Her expression hardened a moment. "It at least gives us more time to find a real answer. A species that can't just... do that... without outside help is barely a species."

You glanced down at your covered and altered genitals. So how had you been changed?

Her expression brightened a little. "The stud program, which you are now part of, is one way to get healthy foals. It is Celestia's hope that infusions of vital male energy from other sapient and pony-like species can help turn this around through breeding, the same way you could skew ponies towards being taller by breeding tall ponies and limiting shorter ponies from it."

Pony-like?

She gave a wry smile at that. "Don't think you're very pony, do you? That's alright, most don't either. But you are! Look." She raised a hoof to her face. "You can understand all the expressions I make without even trying. That's a pretty big connection to start. Your body's script--"

Genetics?

"Genetics? What is that?"

You explained they are the basic instruction set of the body.

"Ah! Yes. The script. The script of your people and our people are the same script, when you get down to it. It's just in the wrong order. Where yours is describing eye color, ours is going on about tail length. With some careful re-ordering, we can breed, and produce perfectly healthy, wonderful, foals. In fact, if we did the same to a mare to bring her in line with your people's order, she would produce one of you instead, presuming a non re-ordered stud laid with her."

Her horn glowed and she grabbed at the hem of your pants with her magic. "May I look?"

Looking, but no touching! You lowered your pants just a little so she could see you were fuzzy down there.

She nodded. "You've been re-ordered. You've also been focused."

About that...

"Your species has the ability to cast the foal-producing spell. From what I've seen, you don't strictly require it. A female of your species will notice an egg and react on its own without being told to. The last female that was brought, that was an accident by the way, told us that they can inseminate a female with seed not from any stallion, though it can, on occasion, have side-effects. Oh, listen to me, telling you about your own species. I'm sure you know that already." She shook her head. "Back on topic. The Princess, whichever did it, took that natural signal you give and turned it up. You can signal a mare now as you breed her, but it's so loud that it stresses your body and aetheric network."

Aether what now?

"Let's not get too distracted. Just call it a magic network. You have one, even if you don't use it often." She reached out a hoof and tapped you on the belly. "So, as I was saying, it gets stressed and eventually something breaks and then that's it, no more studding for you."

So why can't a stallion be focused the same way?

"They can be." She nodded. "But pony bodies are better at self-regulation. Long before they get to inseminating, their body will turn down that adjustment to avoid hurting itself. Your body, on the other hoof..."

So you were made to cum so hard it hurt? Great...

Her expression softened. "If it helps, every stud I've ever spoken to has reported that it's quite pleasant. Most report being more upset that the pleasure stops being so intense when they are expended. That's actually the first way we know a stud is expended."

About that... You realized, if humans are pulled in once in a while, why haven't you seen other humans?

She looks suddenly dodgy, eyes darting everywhere but you. "Some choose to become ponies..."

Some, but the rest?

"And that ends the tour." Careful Study gently nudged you towards the door. "Do stop by again if you'd like, or if you have any ideas. We'll be calling for you if we have an experiment to run."

You got the idea you were being denied. Was it a state secret? Did they do something terrible to any 'expended' stud that didn't accept retirement as a pony?

Author's Note

The results for last time: https://www.surveymonkey.com/results/SM-NNLJ7NXN/

Running or self-exploration were basically not thought of. Meanwhile, that research area sounds very interesting. You'll probably meet some important non-noble ponies there to talk with, and if anywhere is going to have extra pants just laying around, a lab would for covering up naked pony flanks from dangerous experiments, right? Your stomach's rumbling a little, but you have far more pressing issues ahead. Maaaybe if you just so happen to run into a snack on the way, you'll wolf it down.

Or, at least, that's how I read it, and now that this is written, let's write the story.

So you got some answers out of that, and made friend with some guards and a scientist. And clothes! Finally.

What now?
1) Demand answers from Careful Study!
2) You're still hungry, let's fix that.
3) Explore the castle!
4) Try to sneak out and see Canterlot.
5) Relax until Applejack arrives.
6) Try to find Luna and ask pointed questions.
7) Or Celestia?

Have mercy on me, and be sure to include the number of what you vote for.