I known ComperA is fairly well known and I've looked into some of them, but I heard of one that seems to be fairly hard to find simply called "Pregnant With Ponies", though I wonder if that's confused with the Pregnant With Puppies Trilogy (that's all I'm aware exists and that author's stories are somewhat tricky to find in my experience)

There was also A Boyfriend Named Comet that was interesting (not exactly my fare) and I have my own idea that's more fantastical in nature that is more inspired from Pregnant With Puppies with a twist. Actually I have 2 stories in that vein I want to work on, but haven't had much inspiration or time to devote to them

There are several erotica stories available via Smashwords about women bearing animals. It runs the gambit of dogs, cats, bunnies, bears, dolphins as well as equines. I don't think Pregnant with Ponies is that hard to find, tho if it is the same one I'm thinking about it is very old and the main character, Carla (IIRC) only births one.

Paying for this type of content is probably the easiest, but there are some stories out there if you look hard enough. Definitely a niche kink though. Try searching beastiality pregnant sex stories or similar and you'll find a few in the Zoo communities. Would love to find out about more stories if you find any, as these are tough to find. Here are a few sites with this type of content that I have heard of. No links will be posted to sites that I know contains underage content.

First: pregnant with ponies-http://mamabliss.com/stories/story_pregnant.html

Sexstories has a few, but you'll need to search for them with your find function on a web browser. https://www.sexstories.com/themes/76/Pregnant

Check Archive of Our Own (mostly fandom based), Deviantart, and Nifty Archives (mpreg and beast content).

Furaffinity might have some content, but it is mostly fur-related.

If you can track down Susanmichelle formerly of Beastforum, she had a few stories, if you can find them on wayback engine or directly from her.

Kristen's archives has a few stories, including two of Stevie D.'s pregnant with puppies trilogy, but there are at least two more that I can think of on that site: the inspiration for pregnant with puppies, also
entitled pregnant with puppies, and Becoming a Bitch.

Adultfanfiction has some, including pokemon and Harry Potter (snakes and hippogriffs).

Hentai foundry has few a few stories if you search for pregnant content. Just remember to adjust the filters, or the stories will be hidden. Here is a link to Project Pasiphae, which has a lot of alien
pregnancy http://www.hentai-foundry.com/search/sto...haeStories

Finally, Pgfalcon's Play ball! features a TG dog pregnancy, if that falls into the category that you are looking for.

Also, I think one of the google drives in the drives section of this site has a few stories about this sort of thing. Something about being able to breed with endangered species.

A few of the ones I remember from Kristen's Archives

hXXps://www.asstr.org/~Kristen/28/maryjoe.txt
hXXps://www.asstr.org/~Kristen/63/abluewhale.txt
hXXps://www.asstr.org/~Kristen/29/genetic.txt
hXXps://www.asstr.org/~Kristen/31/start.txt

I think there was a story called "A Deal with the Devil" but I am not able to find it, I know the author also did some called "UTC Spider" and "UTC Naga" but I can't find anything, I think it was on furaffinity

Helios, Deal with the Devil is one of PGfalcon's stories, and it is on Furaffinity and the author's website. It is a TG and transformation story (as most of PGfalcon's works are), with most of the sex as an animal with other animals. I did not post a link earlier because the MC is likely underage (a high school trip to the zoo is in the story). I will also mention PGfalcon's Chicken, Chicken, where the MC's are forced to lay eggs and then later transformed into horses and have a foal together. PGfalcon has a story about a guy that dreams about giving birth to a foal while he slowly turns into a woman, too.

While I am at it, Doc's lab is a TF story site, and may have some stories that you may enjoy, though most of them involve TG and TF themes. I am a big fan of "Rebecca" (horse transformation, pregnancy, and birth), and have outlined a number of spin-off stories to work on in my spare time in my AU of the verse (as the Doc meant for the original to be a one off).

Also on Furaffinity, TheNomeKing has several excellent TF stories featuring pregnancy and birth.

Would love to keep this thread going if anyone is willing to share more stories!

You can also find the two "Deal with the Devil" on TGStorytime.

https://www.deviantart.com/muchbirth/art...-758707170

About as good as it gets, enjoy

One I haven't seen is KomperaKlause's Pet Shop series on deviant art. He also has numerous others that are make and female characters that are pregnant with all manner of things.