There are two separate issues here, which get confused and intertwined.
Every building served by more than one branch circuit requires a grounding electrode system. This can be driven ground rods, metal water pipes, "Ufer grounds" (rebar in footings), etc. For safety, metal parts like pipes and ducts should be BONDED to the grounding electrode system. The building disconnect means (typically the remote sub-panel) is to be bonded to the grounding electrode system.
So, no matter what, you must provide "ground rods" or some equivalent at the remote building.
The independent issue is provision of the equipment grounding conductor. The preferred solution for safety is a 4 wire feeder. Two hots, a neutral, and an equipment grounding conductor run between the two buildings. The sub-panel DOES NOT bond the neutral and equipment grounding conductor. The sub-panel DOES NOT bond the neutral and the building's grounding electrode system. The sub panel DOES BOND the equipment grounding conductor to the building's grounding electrode system. This is the only solution allowed by the 2008 National Electrical Code.
THe 2005 and older NEC allowed for the use of a 3 wire feeder in certain circumstances. (In particular, there must not be other metallic paths between the buildings, such as water pipes or phone lines). Two hots, and a neutral are run. The building's grounding electrode system is bonded to the NEUTRAL at the sub-panel. The ground bar in the subpanel is bonded to the neutral in the sub-panel. This saves the cost of the equipment grounding conductor, but is an inferior solution especially in a livestock environment.
The 2005 NEC is still in effect in many (most?) jurisdictions. It takes a while for local codes to fully reflect code changes. So you may be able to do the three wire solution for a little longer. But it is going away eventually, and good riddance to it.
Driven ground rods are there to provide lightning protection. They do little or nothing to provide a fault current path, as the resistance of the typical driven ground rod is 30 ohms or more.
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