Originally Posted by daryl zero
He didn't say that horses live to be 50. He said animals are self-replicating.
Even with junk vehicles, you need fuel and the question is whether there is any fuel available. Since the planets had no life before it, it may have no source of gas, coal or oil. Getting fuel from other planets may have been prohibitive.
It's the far future. They harness gravity, terraform entire planets, travel between star systems and have laser and sonic pulse weapons. Fossil fuels are not a requirement. Especially since they are not a requirement to provide propulsion in this century. If they haven't come up with a way to provide energy to power a bicycle or light vehicle then they must have missed a massive technological evolutionary step.
And again, horses are far more fallible and expensive to maintain than any machine. They require medical treatment, animal doctors, constant care and attention, suffer from disease, injure and die easily, require food crops to sustain them which could be used for humans, etc. etc. etc.
Machines just require parts and fuel which can be made or obtained from any number of sources (as Kaylee often proved to keep the ship in the air) and last a long time. Mechanics are easy to train by comparison to veterinarians. Especially when it comes to simple vehicles and daily maintenance.
A vehicle can last for fifty years very easily. Getting horses to breed without issue for that long, especially when supplies and expertise are apparently very limited, is far more problematic.
But as Oink said above, arguing logic is apparently pointless because most Firefly fans are too zealous to acknowledge that the premise was inherently flawed, so this ends the discussion from me. I think my points have been made pretty clear.