Theshigen writes “All you need is a trebuchet and a water buffalo (or pig) and you get disease and death in the enemy settlement. Thats right, Trebuchets are in Stronghold: Warlords but unlike what youve seen in most strategy games, youll have different ammunition for these big contraptions of death.”
Source: N4G PC Cripple Your Enemy with Water Buffalos in Stronghold: Warlords