Equidae

Horses and donkeys have never been shown in a Fallout game, but have been mentioned on occasion.

Background
Some equidae appear to have survived the Great War and only lived for a short time, before becoming extinct in just under or over a century onwards. One such case is Pugsley, a donkey owned by a man named Irwin who was killed when his ranch was attacked by raiders around 2161. As this was 84 years after the Great War and donkeys do not live longer than 50 years under even the best circumstances, it is probable that small populations survived on a domesticated basis. It is not likely that they would or could have survived in the post-War wild, short of undergoing mutations to help them fend off predators. The Chosen One when talking to Ethyl Wright however mentions the abundance of mare's milk being around among tribesmen.

In All Roads, the graphic novel, every NCR soldier seen in Chance's flashback of the Bitter Springs Massacre is riding a horse. However, given as the animals are seen in a chem fueled fever dream, the content is unreliable, and Chris Avellone later disregarded their appearance. 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.

Scout Leader Jaggy also laments about missing the sight of horses in Appalachia.

A "Horse Marker" can be found in the G.E.C.K. Horses are also referenced to in the description of the Ol' Painless weapon in Fallout Shelter.