I actually have a ewe with a growth/horn looking thing right now. It's black, semi hard, 1/4 to 1/2 diameter, about an inch tall and curls over on top.
I have only had one other with something similar and it just happens to be one of her lambs 2 years ago. That was a show wether and it's growth was very similar but looked a little more like a giant black seed wart. I had to clip it off on 2 different occasions. I put nu-skin (liquid bandage) on it. It didn't affect anything. I haven't messed with what's on the ewe now. Both had the "horn" around the base of the ear.