IMHO, you could use NMC.... but, I have concerns aboout whether you can install it exposed in a horse barn.
I started a thread on a similar topic about barns at a fairgrounds: http://electrical-contractor.net/ubb/Forum5/HTML/000775.html
Horse barns at fairgrounds that have been recently wired are typically all wired in RMC or Schedule 80 PVC.
While 547.5 allows the use of NMC... 547 is silent on whether or not it can be installed exposed, which leads me to believe that it must be concealed.
Horse barns are notorious for dust and cobwebs, which is why they are prone to fires. I think that if you installed NMC exposed you would have trouble complying with paragraph (C) of this section:
(C) Equipment Enclosures, Boxes, Conduit Bodies, and Fittings.
(1) Excessive Dust. Equipment enclosures, boxes, conduit bodies, and fittings installed in areas of buildings where excessive dust may be present shall be designed to minimize the entrance of dust and shall have no openings (such as holes for attachment screws) through which dust could enter the enclosure.
However, others may differ with my opinion. Let's see what other responses you get.
Edited to add 547.5(C)
[This message has been edited by safetygem (edited 12-28-2004).]