Mean biting horse,

MY GF's horse is just straight up mean. He is about 5yo with about 1 year of riding. He was a unhandled caged in a stall stud for about 3 years. But he is just mean as a snake to other horses. He constantly bites them. I thought it was a food issue but having him at my house with 4 acres of knee high grass and he still was biting my horse. Now I just isolate him when he is at my house which isnt often.
Surprisingly he is pretty laid back under saddle and Shari keeps him in check around people. ANy ideas about the biting though other than isolation? I was thinking a grazing muzzle but that would cut down on his food so not sure.

There may be a medical problem going on. Have you heard of cranio-sacral work?

Horses can have headaches or something "out" in their bodies that causes pain and makes them very moody and aggressive. It's worth having a chiro out to check.

There could be a dominance issue from how he was brought up. It could be a lot of things but I'd check out all pain indicators first.

The geldings that I have seen and have owned that were just plain viscous to other horses, I just got rid of. I never found a way to keep them from hurting other horses that were not bothering them at all. I've had horses crippled and chased over fences and if there was a way to change horses like that, I never found it.

If they ride good enough, they are worth keeping penned by themselves. If not, they just go to the sale at my house. The last one I had was a super roping horse -- both in the pasture doctoring cattle and in the arena as a big, 1300# heading horse that could really handle cattle. He was very well bred and exceptionally well trained. I sold him to a man that said he had no problem keeping him by himself. He was very well mannered under saddle. I just did not want him anymore after he ran a really good gelding over a BIG fence.

This horse was also gelded pretty late. We had him tested and he did not have a testosterone level above normal for a gelding. I raised him and watched the Vet geld him. He did not act 'staggy' but was very, very mean. I have gelded many stallions much later and they were not mean at all.

Well, you could get grazing muzzle and cut the hole bigger so he gets more grass. It would still create a barrier between his teeth and the other horse, so that might work ... but I worry that if he can't bite will he chase and kick? Sometimes if they can't get their aggression out one way they find other ways to be mean. If you are dead set on them being together, you can try the muzzle with a bigger hole, but I have to say, I favor isolation just in case your mare gets a nasty kick that renders her lame.

It sounds like he does not have equine social skills. If he was kept in a stall as a stud for three years and had one year of undersaddle work and is now 5 years that means he was probably weaned and put in a stall. So, he may not have had time out with other mares and foals or other yearlings. They sort of knock each other around but learn how to play with and interact with other horses. If he did not learn how to interact with horses, you can't teach him (to my knowledge). The best thing to do would be to separate him. Set up an area where he can live nicely. It can be a pain, I have a 20 year old gelding that was retired after 14 years on the track and he hates other horses. At the age 22, he is now tolerant of other mares but wants to fence fight other geldings. In my opinion, its not worth anyone getting hurt and needing vet bills. If your GF loves him and he's great under saddle set up a small separate paddock and be done.

I agree with Rookie.

A horse like this can learn social skills if you have the right horse to train it.

My old mare was the best at this, she was always alpha but in a nice way. Rarely did I ever see her bite or kick, just had 'that' look which made anything behave.

I had a recently gelded colt off the track, he would not settle on his own, beat up any gelding, so I out her out with him. He tried to be aggressive with her but all she did was walk away and lie down eating. He really did not know what to do, he tried running at her, hitting her with a front foot but she never moved.
When I went to bring them in he was a different horse, he was following her like a lost sheep.
When it came time to turn him out with others if he got arsey then she would just look at him and he would behave.

Horses like her are invaluable and rare to find

Thats pretty much what I have been doing. I don't let him around my horses not even across a fence. Last time I went to her house I had my horse in a temp corral and this guy reached across fence and bit Bo in the face grabbing mostly halter and was jerking on him. Like I said though unless you are feeding, he is perfectly fine when people are around to other horses and Shari doesnt put up with anything from him. After a few corrections here and there he is pretty docile around her. Looks like the "no social skills from birth " sounds to be right on. Guess our best bet is isolation.

I had a horse aggressive gelding. He was a total love around people, and was always well behaved under saddle and in hand. I kept him isolated most of his life, but he eventually mellowed to the point where he could be put out with one or two other geldings.

Some horses are just not very sociable with their own kind.

I completely agree.

When I bought Woodstock back it was a real similar deal to the gelding you're talking about Joe. He was bought as a weanling, stalled until he was a little over 3, unhandled, aggressive rank mess. I fixed it on the human side of things and after he'd had the time out after gelding, my old sorrel mare took care of it on the horse side.

He went into the pasture with her, posturing like a stud and it took her about 30 seconds to put him in his place. She wouldn't take his crap, kept him out of the lean-to (which was pretty amusing, he hated the rain at first, it would be pouring she'd be right in the doorway giving him the grouchy mare stink eye while he pouted standing out in it) same with food, if he was respectful, he got to eat, if not she ran his butt off. He is now pastured with the herd and does well, he's low man on the totem pole.

On the other hand, like Cherie said, there are some that aren't fixable. I've met a few of those over the years too. They quickly find a new home.

Your best bet is to keep them separated or borrow a very set in her ways alpha mare (I also know folks that loan out their old molly mule for the same thing)

While I agree with the isolating, and the possible "horse socially retarded" idea?

I also worry that this horse, deprived of horses to bite, may decide to bite humans, OR conversely, go after other horses when rider is up on him and other horse too, as a result of biting frustration, if you will.

What breed is this horse, and the bloodlines if you know?