FoalsitterHorsemost people worldbuilding: so here's my ideas for a magic system
me worldbuilding: AIGHT who is ready for my 5 hour video essay on how on an edwardian era equine society the existence of neonatal isoerythrolysis leads to the discovery of blood types
Blood! Disease! Worldbuilding!
Finally, after almost a year... it's time for the 5 hour video essay about how ponies discovered blood types, except it's actually a short #WorldbuildingWednesdays thread.
In human blood types, it is possible for a fetus to have a blood type incompatible with the mother's, in which case antibodies can cross the placenta and attack the antigens of the fetus' red blood cells, causing a disease called hemolytic disease of the newborn.
Something similar can happen in horses. When a newborn foal drinks the mare's colostrum, which contains the mare's antibodies meant to help the foal while its immune system is underdeveloped, if their blood types are incompatible it's possible for the colostrum to contain antibodies that target the foal's red blood cells. The destruction of the foal's red blood cells causes the foal to become anemic and jaundiced. This condition is called neonatal isoerythrolysis. (1/3)
This is prone to happen when the father has a blood type that is incompatible with the mother's, and the foal inherits the father's. This is specially likely when the parents belong to different breeds which are more likely to have incompatible blood types, which may cause interbreeding to become a taboo in spite of the Equestrian government's efforts to promote harmony among races.
In-universe, I've given this disease the coloquial name "milk jaundice", as it is a type of jaundice that happens after drinking the first milk.
This disease isn't observed in all species. In real life, it was only first observed in cattle after the usage of blood-based vaccines against babesiosis that would cause a cow to start producing antibodies against blood types it normally wouldn't.
So, my idea is that much like in real life, ponies accidentally replicated neonatal isoerythrolysis in calves when they were developing vaccines against tick fever. (2/3)
This would give them a valuable hint that the cause of neonatal isoerythrolysis had something to do with blood.
From there on, it was a matter of time until, much like in human history, they discovered that mixing blood would sometimes cause it to curdle/agglutinate, and that there was a correlation between the blood of two parents curdling and the newborn foal suffering from neonatal isoerythrolysis. Similar to the early history of blood types in humans, these blood types discovered by ponies would be named after roman numbers: I, II, III...
As a consequence, the Equestrian government would recommend that pony couples seeking to have a foal should contract a lab to perform a quick blood mixing test to assess the risk of milk jaundice happening. (3/3)
Related worldbuilding wiki article: https://wingsik.miraheze.org/wiki/Milk_jaundice
Princess Cadance 
@sweetdreams You're a serious theorycrafter? I would love to hear more about your theory of how ponies discovered blood types if this post is for real. Or anything else you've thought up!
I love discussing and debating well-thought-out theories, and see you have a certain appreciation for the canon, judging by your posts. We might get along. /)
#lore #mlp #theorycrafting #headcanon @[email protected] @pony
@Cadance @[email protected] @pony oh, yes! I have a fandom wiki where I develop my ideas, I've wanted to move it to my own site, but for now I have a place where I throw my worldbuilding
Sometimes I do retcon canon stuff, sadly, but people are free to take my ideas that they like and disregard ones that break canon, of course, I'm not the one who gets to decide what should and shouldn't be canon
@sweetdreams @[email protected] @pony Neato! Are you willing to share a link to that wiki? I'd love to check it out!
I try to stick as close as I can to canon with my own theories but but I admit that breaking loose from it can lead to all kinds of cool ideas. Sometimes it's necessary for certain roleplay or art ideas to work.
I totally encourage moving things to your own site when you can! Wikia/Fandom.com (I have trouble ceding the generic word "fandom" to them - I don't think they deserve it, and feel the same way about Facebook/Meta) is bad for reasons I'm sure you already know well.
Maybe check out @miraheze as an alternative? They offer a much friendlier free MediaWiki-hosting service than Wikia ever will, with real options to leave down the line AFAIK.
@Cadance @[email protected] @pony @miraheze oh, sure! My current wiki is here in spite of the undeveloped main page: https://wingsik.fandom.com/wiki/Library_of_Wingsik_Wiki
Feel free to disregard anything that contradicts thr canon, sone retcons are fairly major
The stuff about the discovery of blood types is in this article: https://wingsik.fandom.com/wiki/Milk_jaundice
And thanks for the suggestion, I'll check out that alternative!