I just completed a piece of a Bighorn Sheep Ram. I took my reference photos this past fall during their rut. It was a COLD day with light snow falling and heavy overcast and although I was hoping to capture some impressive head butting behavior they were more interested in sleeping in. Over several hours of watching I only once saw two young rams hit heads once...sort of... barely... LOL That is just how it is sometimes when you are trying to take photos. Finally one larger ram (the one in my art) did come over the hill and follow two females toward me.
It was a fun and unique challenge figuring out how to create the texture of the horns. Most of it was completed with the fiberglass brush. I use this tool quite a lot for textures that are not fur (and even for fur sometimes). Another challenge was that not only do they have the rings growing horizontal on the horn, but they also have striation that runs vertically on the horn.
If you want to see the up close details you can check out the zoomify version on my web site. It does require flash, but click and it will zoom you in so that you can see every scratch! At least 80% of the work on my web site has this function because I think it is so cool!