Equidae

Horses and donkeys are animals mentioned before and after the Great War.

Background
Equidae are mentioned many times, though no living examples are ever seen in-game. Donkeys survived the aftermath of the War for at least a few generations. The status of horses is debatable. Horses have occasionally been mentioned in ways implying they have survived, and have also been seen alive in non-game sources, and developer comments contradict each other on whether these are mistakes.

Mentions

 * Dane, one of the Children of the Cathedral, will mention horses in his ramblings.
 * A donkey named Pugsley was killed by raiders shortly before Fallout. This was multiple donkey generations after the War.
 * The Chosen One, when talking to Ethyl Wright, can mention the abundance of mare's milk being around among tribesmen.
 * There is a book entitled Pretty Pretty Horsies: A History of the Mongol Empire available in Fallout: New Vegas. It is a quest item for convincing the Great Khans to break their alliance with Caesar's Legion, by revealing the history of their namesake ancestors.
 * A "Horse Marker" can be found in the G.E.C.K. This is a leftover from The Elder Scrolls IV: Oblivion, similar to the unused "Rumors" function in quests.
 * In the Fallout: New Vegas add-on Honest Hearts, the war clubs used by the Dead Horses have been carved into the shape of a horse head.
 * There is a drawing of a horse, chicken and cow used in a framed picture near Bunker Hill in Fallout 4. The same drawing appears at an unmarked trapper outpost northwest of the MS Azalea, in the add-on Far Harbor.
 * Horses are referenced in the description of the Ol' Painless weapon in Fallout Shelter.
 * A toy called the Giddyup Buttercup was popular before the war.
 * On the cover of Tales of Chivalrie, a knight is seen, riding a horse while fighting a dragon.
 * A horse is part of the Paul Revere Monument in Boston.
 * Scout Leader Jaggy laments about missing the sight of horses in Appalachia.


 * Non-game
 * The donkey from Fallout is commented upon in the Fallout Bible.
 * In the graphic novel All Roads, an NCR soldier seen in Chance's flashback of the Bitter Springs Massacre is riding a horse.

Behind the scenes

 * On January 24, 2013, Fandom user "StylesV13" added a quote from a personal email purporting to be from developer Chris Avellone. The contents of the email pertain to the appearance of horses in the All Roads comic as "an error (no one noticed it until too late)", Raul Tejada originally mentioning horses in one of his stories, and stating that horses are completely extinct in the Fallout series.
 * The contents of the email cannot be independently verified. While a quoted portion has existed in this article since 2013, the screenshot of the email did not surface until 2014 where it was uploaded by a different, unrelated user on a separate website. Comments on the file suggest it was taken from the now-defunct Bethesda forums, but a link to the original post or thread has not survived.
 * When asked about the StylesV13 email about horses in September 2020, developer Joshua Sawyer commented that he was not immediately familiar with the horses appearing as an error in All Roads, the concept of horses being completely extinct in Fallout, or Chris Avellone expressing it. He had "no idea" about this information, and that if he ever knew, it was "lost like dust in the wind."