I only have one experience, so can't answer.
Hugo was just 7mos old, but he is big. My cousin has a farm and said there were 7 sheep "out there somewhere" and sure, see if Hugo could find them. So early the next morning, we went to the empty barn and pen, he got a nose-full, I said "Let's find them and bring them back here!"
Was all I could do to keep up with him, he found them sleeping in tall grass, they took one look at him and spooked, he chased them a bit,
came back to see how I was, they slowed, some lay down again, when we got near, they booked to the barn. Wasn't really any work involved, other than "tracking" them, as they wanted nothing to do with him, and scurried to their safety zone. I leashed him up and didn't let him hassle them as soon as they beat feet into the corral.
It was interesting and fun, but not much of a test. They live a good 10 hours from me, so haven't done that but once. Of course, I told him he did a great job.
They are prey animals, dogs are predators. I wouldn't expect that they are going to challenge, but instead show some nervous fear.
That ought to embolden your dog, and it ought to play out as it has for eons. Horses, they too are prey animals, but their size is so much more formidable, I'm sure most dogs would think twice. Cowboys on horses herd horses, not a single shepherd and his canine. I'm sure there are dogs who do, but I doubt many just started out herding horses day one!
Have fun! Kick some booty Mikko!!!
I know what CGC means, but TN-N, NJC, NAC, TG-N, WV-N ?