dogs rolling out

I dont know if you train them to do it or if it is geneticsyrs ...it just happened to my cat gyp. She is 6 yrs old now, but when she was two, she found a hog one day and we caught that hog with just my gyp and the catchdog. Right after we caught the hog, we started walking out. I didnt have my gyp on a lead rope, I just let her run loose. While walking out of the woods, she picked up another hot track and found that hog too. Ever since then, she knows there is more than one hog in the woods. She has rolled out after every hog since then. That doesnt mean she finds one everytime she rolls out, but she will roll out (unless it has been one of those 8-10 mile races, then she is usually done). Sometimes I try to catch her before I catch the bulldog, if I dont catch her, she just keeps going looking for the next hog.