Horse

Horses are a domesticated quadrupedal mammal mentioned in the Fallout series.

Fallout
Dane, a member of the Children of the Cathedral whom had his brain fried after using mind altering drugs, mentions horses in one of his random ravings he gives to the Vault Dweller. "I want a horse! I need a horse! Bring me a horse, dammit! A horse!"

Donkeys, a related species, survived for at least several generations, with Irwin mentioning he had one as a pet until raiders attacked his farm in 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.

Fallout 2
During a conversation with Ethyl Wright, the head of New Reno's Temperance Union, the player makes mention of drinking "fermented mare's milk".

Given the context of the conversation, it is likely that the player is tweaking Ethyl's prejudices about tribals by mocking a stereotype. The idea of fermenting mare's milk, or that it could even be fermented to begin with, could have come from a pre-War book on ancient nomadic cultures. Alternately, the player could be referencing the practices of neighboring tribes – for its own part, Arroyo shows no indication of having ever possessed horses.

Male Casino patrons also make a sexist remarks about how they want the Chosen One—if female and a Porn Star—to be their "main filly" of their heard. This is explicit evidence about the average persons knowledge of horses.

Fallout 3
All horses mentioned in Fallout 3 are of pre-War.

Honest Hearts
The Dead Horses' war clubs have a horse head.

All Roads
A graphic novel written by Chris Avellone, All Roads shows pictures of horses, but only in Chance's memories, and then later as part of his drug-addled flashbacks of the Bitter Springs Massacre. In these flashbacks, NCR soldiers are riding horses. Chance may have previously seen pictures of people riding horses in books, on posters, or in other similar pre-War media, but Avellone has previously stated that horses did not survive the Great War in the area of California. Avellone later admitted that he did not intend for horses to appear in All Roads and that the graphic was released before anyone noticed that horses appeared in it.

It is unknown if horses survived anywhere else in North America.