I have a couple thoughts on aggression and herd dynamics having had experience with different herds as a barn manager and owner/trainer. I work with a mare now who I USED to call the "Battle axe" for obvious reasons. I've known her for years and I learned from her and my other mare who used to be more submissive, that the chemistry is based on who they are with. So as I moved them to different barns and herds, they changed in dynamic. The "Battle axe" when mixed with a herd she approved of was actually more or a "Lead" type horse. When mixed with a herd she didn't approve of, back to "Battle axe". My other mare had lived in several locations throughout her life. Generally being the bottom to middle rank in the herd. She was moved to a barn not so long ago that had a large mixed sex herd (of about 14). For the 1st few weeks she took a BEATING. I was concerned, then all of the sudden she switched to taking top rank and became a "Battle axe" for the first time ever in her life. She was the one to be reckoned with. So I had the chance to watch the horses interact in different herds and see how they faired in different situations. I do step into my herds and shape overly aggressive behavior when I am around. And have seen that it helps most when you are the primary care giver of the horses ie. they live at your place or in my case I manage the facility and therefore set the "tone" of the energy at the farm. I have seen this in action at many farms. Whoever the primary caregiver is dictates the energy and flow around the barn for good or BAD. If the person is timid and lacking leadership skills, the horses run the show. And that is where problems occur often.
I also have owned and worked with stallions. I take special care to keep them socialized and when matched with the right energy level geldings or other young colts, they actually do very well and get to play and rough house as boys can and should be allowed to do.
Horses in the wild select their herds and mates. I have seen over and over again, my show clear preference for one horse over another. Especially, my mares. They live with one gelding and are basically companions, then they live with another gelding and are madly in love with him. A Clear preference. I think when horses are under socialized or live a life where they don't have any interaction with other horses, their social skills are stunted. I have seen this with horse that previously lived alone and I had to integrate to a well socialized herd. They have a bit of a time at first learning the "rules" of that particular herd. I have also relied on Benevolent herd "Leaders" who are balanced and even handed to help me straighten out my little "Hoodlums" or young colts and teach them manners and rules.
I feel like if we have a good understanding of herds and the horses you are putting together AND a good amount of space for them to work it out in, It should be a relatively smooth transition with proper preparation, introductions,and leadership.
Saddle balance is as important as saddle fit to your riding position and communication with the horse. Do not assume because you saddle tree fits it is also balanced.
I recently went through a tough time fitting my horse, Mercury because he is what's called "uphill" in his conformation. Meaning his withers and back slope uphill from his hind end. He is very nicely built for natural collection, balance and dressage. This is one of the reasons I bought him. It has proved to be a fitting challenge though as my saddles fit in the tree size but all sit "down hill" on him. Meaning the back or cantle of my saddles sit low compared to the front making me feel as though I am sliding backwards. Now I am fighting for my balance against my equipment. To any rider this feels horrible! So imagine how much uneccessary muscle strain you are using consciously or unconsciously because of this. Now if you are straining, you are communicating tension to the horse as well as concentrating on balancing instead of riding and communicating with your horse. You are also possibly unbalancing your horse as well unintentionally. This can feel like the horses gaits are choppy and fast when he is out of balance. Also, our imbalance can cause a horse to be tight in the back and hold his head up in tension to compensate.
I find that western saddles often sit "down hill" on horses. Meaning the front of the saddle is low compared to the back. One reason is a lot of Quarter Horses are built and bred that way. The other is poor fitting saddles. Now you may say " my saddle looks fine it's higher in the front, but your not looking in the right place. You need to look at the spot where you sit. See if it looks level from the ground and more importantly "feels" level when you ride. Sometimes you have to sit in a few different saddles on a few different horses to note the differences in balance good or bad.
So now your thinking how can I fix it if it's off? Well IF your saddle is sitting high in front or back you have to check on a couple things first. If it is low in front it can be too wide of a tree for you horse which can be remedied by using a pad that is designed thicker toward the front then the back. These are easily purchased in western and english styles.
If you saddle is sitting high in front, you probably have too narrow of a tree which is not good. This can pinch and restrict movement, bending, willingness to go forward, cause soreness and muscle atrophy in the area. DO NOT ADD PADS the small trees! You are taking more space away and can create even more pressure points. You need to get a tree that fits.
If your tree fits and is sitting low in back (like mine), you can get a pad that is built up in the back and not in the front. My saddle I had specially made with the back built thicker in the panel so I didn't have to use a pad. I don't like using extra pads. Unfortunately, western saddles don't have any padding you can add into the saddle so you are at the mercy of just plain good fit, custom fit, or specially designed pads. If you are unsure of your eye and feel ask a qualified fitter in your area for help.
I love finding out something I have been doing already for years, is now recognized by the medical community as fact.
Alfalfa has been villified by many a horse expert throughout my experience in the industry. It supposedly makes horses crazy, causes mineral imbalances and is far too nutritious for most horses.
I have been feeding alfalfa for years in the proper amounts to everything from minis to warmbloods. The reasons I feed it are this, It possesses nearly every vitamin and mineral we and our horses need, It provides cloryphyll (if your horse isn't on grass he needs this) it is a good supplement for our ever depleting hay nutrition (due to poor seasons and soil quality), Even if your horse is on grass, most grass pastures (unless strictly cultivated) are depleted of any real nutrition.
Now let's talk about the medicinal qualities of Alfalfa. It can reduce arthritic inflammation, It has been shown to be a healer and preventative for digestive issues and Ulcers. This is one of the main reasons I feed it. It can help balance hormones (any moody mares out there?), It is a detoxifier, It improves milk production. It is good for low carb low sugar diet needs. The list goes on...
I feed it with Oats and sometimes Kelp to keep minerals balanced but it really depends on accurate testing to find out if the Calcium/Phosporus ratios are way out of balance. With the right mix you should need little or no supplementation for any horse, Mare, Foal, Stallion, or Performance horse. And as we know in our own diets, whole foods are better then processes foods. Remember to make feed changes gradually and consult with your vet to see if it is appropriate for your horse. Avoid the cubed form if at all possible, they can cause choke.