If you would have checked a few lines down you would have noticed these threads:
http://forums.taleworlds.com/viewtopic.php?t=5332
"I cant give my people gear...." On page 1
OR
http://forums.taleworlds.com/viewtopic.php?t=5131
"How do i equip my troops please help!" On page 2
I guess that thread (or the other) would have answered to your question also.
So, check the latest upgrade tree to see which units have horses
*edit* Here:
http://forums.taleworlds.com/viewtopic.php?t=5151
My point is that it's better to check the topics of the first two pages before going 'search', as it is always tricky... using search i mean...
So we don't end up discussing about the same topics every page... Though trough repetition comes mastery... or something...