Originally posted by sauron
plus their horses died in fotr when arwen used the power of the elves to set the river on the nazgul, those horses are the only ones who would not be terified of the nazgul, plus even if they could ride other horses, where arw they going to come from, gondors really going to give mordor horses (sarcasm) and if mordor had other horses of its own, dont you think they would have orc cavalry, giving a clear advantage
in the book they had horses, THEY HAD HORSES I TELL YOU!!!! and (replying to someone else's comment) it'd be easier to put them on horses, because they are living, and actual creatures, instead of using computer special effects
(back to sauron's comment) in the two towers book, eomer told aragon, legolas, and gimli, that the ringwraiths stole thier horses from rohan, and only the black ones (duh) so they could just steall somemore