According to the state veterinarian's office of Mississippi, there are no specific regulations stating how a stallion is to be confined, but there are regulations regarding loose animals. You can find the specific livestock and fencing laws for Mississippi at the following Web site: http://asci.uvm.edu/equine/law/fence/ms_fnc.htm.
Note that Mississippi law does give permission for someone who catches and confines a stallion that is running at large (beyond an incidental "escape") to geld that animal.
