This is also a new requirement in Ontario.
Now, a ground will run with the circuit conductors and a ground rod at the building would only be connected to the panel enclosure. Every panel will be installed as a sub panel and the bonding screw must be removed from the neutral bar and the neutral conductor isolated from ground.
My understanding is...
First, this is only for new installations.
Second, the secondary service would not have a ground rod installed. The panel enclosure would get attached to the bonding conductor and ground back at the CMS.
Third, this is only for buildings that house livestock. The farm house, driveshed, etc. can still have it's own ground.
Because these buildings are usually fed underground, the conductors can be damaged. It's possible to lose a hot or a neutral. With the new requirement, it will be possible to lose a ground connection, too. A broken ground wire would allow the system to operate normally but the ground at the building would float.
Actually my experience has been that overhead wiring is more prone to damage. But regardless I guess that our job is to try to minimize that possibility.
If this helps, here's the rational from the Ontario Bulletin that addresses this...
"It has been demonstrated that the use of the bonding conductor run with the feeder conductors provides superior safety performance for livestock. The fact that the earth serves as a parallel path for neutral currents back to source is to be considered as a cause for stray current problems for livestock. It has been well recognized and proven that re-establishing neutral grounding in buildings housing livestock, does not eliminate problems with voltage transients and tingle voltage which has an adverse effect on livestock. Additionally, Rule 10-200 requires that grounding be arranged so that there is no objectionable passage of current over the grounding conductors. It continues by indicating where, through the use of multiple grounds, an objectionable flow of current occurs over the grounding conductor;
• one or more of the grounds shall be abandoned;
• the location of the grounds shall be changed;
• the continuity of the conductor between the grounding connections shall be suitably interrupted; or
• other effective action shall be taken to limit the current.
A current flow that causes damage to property (livestock) would be considered objectionable and therefore should be mitigated by one of the methods shown. However, this method of grounding will not mitigate the utility source stray currents."
(Hopefully I haven't broken any copyright laws by posting this.