How to correct young mare 's aggression?

You say they are "spoiled" but have not mentioned what brought about the bad behavior in the first place?

You also say that after finally accomplishing lunging and taking them for many walks and working with them in the round pen that "we are ready to pony them with our horses." What accomplishment? The accomplishment is retraining them and stopping the aggressive behavior before ponying them to your horses.

Does not sound like they were trained properly and are showing this aggressive behavior because the training has become redundant from doing this for a long time. Horse like a schedule but they can become bored and angry when things have to be repeated on a day in and day out basis. Break up the routine and do other things.

It also sounds like that the behavior resulted during their training. So its time to get a professional trainer to help you before their behavioral problem get's worse. Or if you already have a trainer, its time to find a new one and get their advice on the situation.

The mare needs to go through a slow and proper introduction with other horses an arena and pasture before she can work with horses or be "ponied to them"

EDIT TO YOUR ADDTIONAL DETAILS:

Amazing that in the first part of your question both horses, especially the mare were showing aggressive behavior, nipping, biting and turning their rump to you on more than one occasion and now all of a sudden they are more respectful in your additional details. As if all of the advice helped in twelve hours. Tis a miracle, realistically it takes more time than that.*End Sarcasm* Your original post says that the mare is dangerous during lunging in the round pen, but in the additional details you state that the mare now is fine when you lunge her after a month.

No denying there is still a problem and you ponying both of them before they are ready. Aggression is not something to ignore and move at your pace.

You sound impatient to pony them around and have ignored the both horse's most especially the mare who is trying to tell you she is not ready, but then started showing aggression because its the only to tell you to slow down. She may need to be checked by a vet to make sure she is okay. She may need to have her teeth floated.

You make no mention of the mare's supposed progress of getting along with other horses in the pasture and in the barn.. You said she was not properly socialized with other horses or was never around horses from the time she was born. Which again it would not be a good idea to pony her to your horses around the neighborhood till she is fine with other horses. That would be an important part of training too.

Most everyone here agrees that you should get a trainer or second opinion from another trainer.

These horses are not ready to move on to "the next step" at all. They need to be shown ground manners first of all, once they respect you, you won't have to worry about them trying to kick or bite at you or other horses because they should be focused on you. These horses sound like they have had no training at all. If you were training correctly these issues would be gone after the first 3-5 days of training. These are simple things that should have been taken care of when they first demonstrated this behavior. Being as young as they are, they should learn a lot faster than a 4 or 5 yr. old horse. This is not habit for them yet, they just think they can do whatever they want to you. Absolutely no respect if they are trying to nip you or kick. I suggest watching some clinton anderson videos and sending them to an actual trainer that knows what they are doing. Once you get them back from the trainer they will eventually try and do the same stuff again unless you know how to properly correct them which is why I say watch some clinton anderson videos. You are no where near ready to train a horse if you can't even fix simple behavioral problems like you mentioned.

so basically, you want to know how to keep doing a crappy training job.

A RUSH job.

Sorry, but when you claim the mare and gelding are "Ready" for the next step..ponying...YET you clearly say that both have STILL done stuff like trying to kick and bite...

You are RUSHING them ad NOT doing a good job and are actually making them worse.

Go at THEIR pace. Find out what you are doing/not doing that has not let them get past their unwanted behavior.

Horses aren't stupid. They think that people are stupid and they sometimes "need" to put people in their place....when people are not clear and don't teach them right.

These horses are sour and need to be restarted and trained in a calm and consistent fair manner so that they are 100% WILLING to do everything without ANY fuss.

So...as long as they are both fussing, you should STOP wanting to "move forward" and fix these issues.

The mare sounds sick of being round penned in however you are doing it. She's angry.

You're not round penning correctly.

The gelding also, is still dominant or bored...and still nips/bites.

Find a trainer to help you.

Sounds like your understanding of horse behavior is somewhat lacking. Horses cannot be spoiled. They can be taught bad habits by owners that are not well informed. A horse turning their butt to you is a sign of disrespect but you have to EARN respect from a horse, it is not given as a gift, you have to deserve it and that is obviously not the case here. With some lunging and going on walks, these horses are not really ready to be ponied. They are still greatly lacking in their foundation training if one considers the general procedures of the most accomplished trainers in the business. None of what you describe is agression, these horses are just not well trained, they have very little training actually. Trying to do too much too soon just makes for more problems, sooner or later.

Nipping or biting has to be interrupted. No hitting, yelling, kicking, etc. Before a horse bites, it has to get ready to bite. You have to learn to recognize that intention, have a steady rhythmic behavior in place with the horse so that you can interrupt the biting behavior. If you miss your opportunity and the horse has already tried to nip at you, you are too late, just ignore it and try to be better prepared next time. You just have two seconds to correctly respond to a horse's behavior so that you can have the opportunity to successfully teach the horse the proper response. The failure is always on the part of the human,never the horse. You said yourself that the mare had never been around other horses so you answered your own question as this is why she tries to kick other horses. You need to wait until she is better prepared because it is better for her and it is the proper thing to do. Again, from what you described, the training here is too limited to expect too much other than what you have already gotten from these horses. Always do what is best for the horse.

so basically you are "going to ignore this particular problem until it bites you on the ....."

wow they are really young. so you need to work at their comfort zone.

you need to go back and start all over again

start with the basics. talking to them giving treats getting them used to you being around them, talking to them. do halter training. get them used to being groomed and working with their feet. how do they do around a farrier.

do not rush the training that is a big mistake. bad owner, very, very bad.

aggression is what happens when they are scared and unsure.

introduce them to the other horses. i am not sure how many you have but try the most mellow horse you have fist. put them in pasture or round pen together or some smaller space so they can bond. one by one do this with all your horses. there should be a barrier between them at first so they can not do much damage. (gees this is horses 101 have you read nothing, watched nothing?)

you do more damage to animals when you try to rush them and do what you think they should be doing and not what they feel comfortable doing.

EDIT: now try more back peddling you say first your horses are aggressive and then you say in additional details they are not all that aggressive i am confused

You obviously have training issues, are facing natural herd dynamics, or both. Keep working with both, and consider who you are ponying off of. I once tried ponying the horse at the bottom of the herd off of the lead gelding. Bad idea, never doing that again.

ETA: These horses are not ready to be ponied. I realize I'm basically repeating what you have been told time and time again, but it's so important that you don't rush these things that I'm just going to reiterate it.

Also wanted to add something - while I TD'd Lilian's answer, there is a grain of truth to it - you should not put up with aggression. If these horses turn their butt to you aggressively, you do need to pop them on the butt for it. No need to whip them for it like Lilian suggests, but do show them that you won't be tolerating a threat to kick. However, don't hit them every time they turn their butt to you - only when it's done aggressively. Ears pinned (not simply turned back - know the difference), hindquarter muscles bunched, etc. is showing that a horse will kick. However, if the ears are relaxed and the leg is on the ground or resting, the horse very well could be expressing that she's comfortable enough with you to turn her back and not keep and eye out for you to make you're not a threat. Just be sure you know the difference.

Oh, and stay out of the way when you pop them! They will sometimes try to kick back!

Work the horses in the round pen some more, they are not ready to be "ponied".

Novice horse owners will give me more thumbs down! But, horses that are aggessive have to be shown that you just will not permit those actions. If she ever turns her but to you you should, whip her hinder hard! Those wussy little telling them 'no" and tapping them on the shoulder will not work.

Do not put up with agressiveness or it will just get worse.

If you are ponying her on a short line, with her head tight to your knee, she can not turn and kick. If she shows misbehavior, make a hard left turn (away from her) and continue on BRISKLY. A horse thinking about keeping their feet moving doesn't have time to bite and kick.