gelding being mean

Question
I have a 6 year old gelding ,very sweet horse,I've never had any problems with him. I've rode with other horses mares and geldings , hes been fine. We just bought a 2 year old arabian filly, we put them together , my gelding started acting studly which he has never done before , he  got hard and actually tried to mount her.
The next day he got really mean , he bit her several times knocked her down and finally ran her off , she had to go clear to the other side of the pasture to be safe. When I try to get him close to her he freaks out ,he starts shaking and acts like he wants to kill her, Not my horse at all. What is going on?

Answer
Hi Brenda,
First the obvious question. Are you sure your horse is a gelding. I know it sounds like a silly question but I have had folks bring me "geldings" that were not. It is possible that your horse is "proud cut". He would still show the properties of a stud but not be able to procreate.
Another possibility is that he was gelded after he has bred. He would know what to do, just not be able to do it anymore.
I would start out with him on a lead line and rope halter a little ways from the filly. As soon as he begins acting up, put him to work. Lunge him in very tight circles at a trot with tons of changes of directions until he begins to listen to you. Don't go any closer to the filly until he is listening to you. Once he is, close the distance a little and start the process over again. Do this until you can stand him next to the filly without him acting up. If he does act up, do it again. What you will be doing is, make the wrong thing hard and the right thing easy. he will find that it is just too much work to act up and will want to stand still.
Good luck and please stay safe.
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blpdoc82652@yahoo.com
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www.yazooequinetraining.com