Horse

Horses survived the Fall.
Most people think it was thanks to the protection granted by human populations. Others, in fact think that they would have been eaten by humans, and their survival is explained by tough feral populations living in remote places.
Whatever the case, horses are still the most common means of transportation in the Afterfall, for those capable of afford such thing. This may not be the case in every settlement, but in at least 2/3 of them horses are the norm.
Most horse populations have developed mutations, just as humans have, in order to endure the harsh conditions of the Afterfall.
The most common mutations among horses are Water Efficiency - 1, Efficient Digestion - 1, and Tireless - 2.
Horse breeders usually select and develop breeds that come with certain desirable mutations, suitable for their surroundings or the most common purpose of the animals.