The Western relationship with horses, especially in the UK and Europe, is long-standing and very complex.
Horses are technically 'domesticated' but no one would ever imagine cooing over a horse in the same way they might a dog or cat. Instead, there's a certain amount of dignity that comes with the human/horse dynamic: A sense of inherent respect for the ever-untameable spirit of the stallion and the eternal elegance of a show horse in dressage.
Horses are, even when owned, a commanding creature.
The aesthetics of the horse seems to have an extreme appeal too. Horses are paired with rulers and nobility in art (their heads deliberately shrunk to exaggerate the strength of their owners) and studied extensively by the great masters. For many (myself included) the most striking painting in London's National Gallery is George Stubb's Whistlejacket.
The prominence of ponies and horses in Western culture was inevitably going to bleed in to kink culture and pet play. And, much as you'd imagine, its erotic existence is just as uniquely interesting as our relationship with the animal that inspired it.
Pony play is a sub-genre of the pet play fetish, which involves at least one handler/owner/trainer/sir/mistress and at least one individual who takes on an equine role.
Even the briefest glance at the pony play kink will reveal its heavy BDSM connotations. Most noticeably pony play highlights bondage and domination, with its many forms of restraint (inspired by horse riding tack and described as such).
Given this, it's no surprise that there are two main types of pony play scenario: Those involving people who fully embrace equine roleplay (they are naturally horses) and those who are being 'forced' in to their tack (they are humans being treated as horses). In the latter case, humiliation fantasies may also be at play: with the position as a master/mistresses' new play thing being the main point of arousal.
Either instances usually involves three different types of pony. There's the Show Pony, who gets dressed in pretty tack and must meticulously model their gear; Riding Ponies, who will be ridden by a dominant; and Cart Ponies, who must cart their dominant around (sometimes in public) and may be whipped for motivation. In all instances, tack, riding crops, and whips will likely be employed and various degrees of humiliation or praise are possible.
These extensive subdivisions are fairly intricate and stand out for their complexity, even among the pet play community. There may be different dynamics for pups, a fluctuating relationship with pussies, and an almost mainstream vibe to bunny girls and boys, but pony play takes the red ribbon for categorisation and presentation.
As is expected, the somewhat stand-offish and almost professional relationship dynamic present in humans and horses also allows pony play to be more transferable to a conventional BDSM relationship. Affection doesn't necessarily exist as a fundamental requisite of any play scene. Things can remain purely rider and beast and that shows in the framework of pony play itself.
But another standout element of pony play is that it's well known outside of the kink circuit and people seem to like it...a lot.
My first experience with pony play was as a teen and it wasn't what you'd expect.
I didn't stumble upon it accidentally while browsing the net.
I didn't slip myself in to a sex museum to get some 'alternative' (and probably more efficient, at that time) sex education.
Instead, I saw my first pony on the middle shelf of a high street magazine retailer on the front of the now retired Bizarre magazine.
This was at least ten years ago and, although not exactly pervasive in society, pony play was at least accessible.
Now pony play is never that far from public exposure. Traditional 'bits' are sold alongside other ball gags in most adult stores and high-class cat walks are becoming a bit more equine; with hoof shoes gaining so much attention that they routinely trend on tumblr.
Fashion seems to be the conduit for most people's exposure to (and acceptance of) pony play and I count this as kind of inevitable. Pony play gear is well-made, inherently elegant, and has immediate fashionable appeal. This seems to have readily drawn people to pony play, or at least its gear, and through fashion people have learnt to embrace fetish.
This is very reminiscent of people's relationship with corsets and leather gear and is both a good and a bad thing. On the one hand, it helps to normalize fetishes and niche desires, which is awesome! It also means that undiscovered ponies will have more chance of finding their herd, minimalizing isolation. But, alas, this does also trivialize the intricacies of pony play too and contextualize it in ways far removed from the fetish itself.
The popularity and acceptance pony play has been afforded doesn't seem to have transferred to other pets, either. Pups, particularly, are still approached with ridicule or scepticism, and this is a shame.
It is people outside of the pony play community, not the community itself, that have caused this dissonance. As such, there's not much to be done except put one hoof in front of the others and keep representing pony play with pride.
There are, thankfully, many fully-fledged pony play fetish communities willing to teach new ponies the ropes (or reigns), and you're almost guaranteed a warm whinnying welcome.
Just be prepared to save up: tack is not cheap.