Elite Herds is just the precursor building to Warlords Horse Herds and offers no recruitment, recruitment from the Warlord's Herds building is dependent on AOR of steppe units (and, of course, faction). I forget what units the Pahlava get out of them (some kind of noble cavalry I believe, plus regular horsearchers with pastoralism- Pahlava is the only faction that can get regular, non-noble horsearchers with pastoralism). The building line is upgradable all the way to High King's Herds, which is where Parthian Cataphracts are recruited from, I forget what the levels in between are called. When upgrading a settlement to get the reformed government, building the Settled Aristocracy upgrade disables recruitment for the herds line. Recruitment with the Reformed Government depends on regular MICs like most factions get. Those MICs are what get you the ParthoHellenikoi Thureophoroi (your first crack at decent infantry), Kardaka Arteshtar (Persian Hoplites) , and the highly feared Grivpanzers (Grivpanvar- late Cataphracts), plus you can get most of the old (pastoralism) steppe and regular Eastern units depending on AOR.