Gelding becoming very aggressive in field

I have an 8 year old breed stalk paint gelding, iv owned him for about a year and a half. He's well mannered with people, and dogs, but when he's with horses on his own he has a tendency to be a jerk. Up until recently, this hasn't been a big deal. He'd chase them, and some would come in with some bites or kicks, but it never got out of hand, and if it did, another horse Norman (the only horse above mine in the herd) would step in, give him a good knock, and that would be the end of it. Recently my horse has been more aggressive in the field, he'll pick certain spots that are "his" and chases horses away from it and keep chasing them, then run up and down that spot so nobody would come back. And for some reason he seems to have it out for a 25 year old Thoroughbred gelding in the herd. Again, was never out of hand. Until last night where he chased this gelding down and beat him to a pulp for no reason. My Barn Manager (and friend) texted me at work saying "took your horse out the big field, lunging him", and has placed him on solitary confinement (in a field alone) until further notice. Apparently he beat the older gelding up pretty badly, he doesn't need a vet call but he will be off for about 2 weeks at least because of my horse.
I'v also noticed little things, like going on a road ride with my friend and her mare that he adores and gets alone great with, and he started pinning his ears (legit pinned back, which I rarely ever see him do), and lowering his head and neck. Almost in a snaking motion.




So my questions is. Why so aggressive, so suddenly? And why just this horse?

I have a theory. My theory is that he is just, bored, and a jerk. And takes his boredom out on others. I come out to see him on my days off, but don't always ride, and when I do, ill admit lately iv been lazy so he hasn't been worked to exertion. Also we just got over a heat wave, so during the heat wave (about a week) he wasn't ridden or worked at all.

We also have a new horse on the property, a younger mare, she's not in his field, but in a field adjoined to his (well his old, none solitary one)were he could see her. And the gelding he beat the snot of, was infatuated by her. Could that effect the situation? Even tho she's not in the same field?


Also not sure if its important. But he's on half a small scoop of textured sweet feed at dinner, just so he can get his supplements (glucosamine, farriers formula, and biotin) and other then that he's on turn out in a grass field, with access to hay as well.

Any opinions would be appreciate it! Sorry for the novel

It could be the Mare. When I moved my Mare out to my barn, we had a gelding who INSTANTLY became obsessed with her. They weren't in the same pasture, and even had an alley way between them, he would still chase all other horses off away from her.

I had a horse aggressive gelding. He beat up many a bigger horse than he was over the years. He was in solitary confinement most of his life because of it.

It's not 'all of a sudden', his aggressiveness been escalating and neither you nor the BO have noticed. That's not unusual, especially since he's boarded and the BO has other horses to tend to, and you're not there 24/7. He obviously has a dislike of the TB and just decided he'd had enough. It happens, especially if there's a new mare in the vicinity.

My gelding loved people. He was a gentleman in hand and under saddle, but in a herd situation he WOULD hurt other horses he didn't like or who challenged his authority.

There's nothing you can do to make him 'behave' in a herd situation. Either find one or two horses he's compatible with, or keep him by himself.

I used to ride a gelding that was a complete arse in the pasture. He was seriously injured with a hock injury do to his aggressiveness and picking on the wrong horse. The biggest thing that led to him calming down was having his feed cut, and working him like it was nobody's business. Only then was he allowed back out into the pasture, and only at night so he couldn't challenge the TWH's that were dominant over him.