My husband and I work cows on the weekends, I only have one gelding that gets excited like you described. I've had him for years, and when I was a teenager, the first time he was around cows I made the mistake of entering him in a fun little team penning competition. He did well, but he got the idea in his head of "check it out, these things are scared of me!" and then he goes on his little power trip.
When I started working cows with my husband, my horse had no fear of the cows, but was also ready to stroll right into the herd and chase something! I knew nothing of cow work the first time I took him out there and that has made it a little harder to actually use him for cow work since then.
I have brought several horses that I have started out to work cows and even if they are curious at first, they settle right into the slow work and have no problem walking in with a herd. My gelding, who is beyond trained 95% of the time, still loses it just a tad when he sees a cow. He has learned to contain himself, actually, the last time we worked cows he was in a plain nylon halter with reins because hubby grabbed the wrong bridle. He's just spent a lot of time walking pastures, staying focused on me,and being tied to the side of the cow pens. I learned the hard way to start my cow work slowly.