The law requires that you remain stopped until such animal(s) pass (when traveling in opposite directions) and that you must use reasonable caution to pass such an animal (when traveling in the same direction).  These provisions are contained in the same statute that governs the passing of school busses (MGL Ch. 90 Sec. 14).  A violation of this law is subject to a $250.00 fine and more importantly poses a serious safety risk to motorists, the animals, and their owners.
–– Chief Mark M. DeLuca