They are usually called a "Saddle Pannier" vs just plain pannier. Meaning that they are designed to be used with a saddle. Saddle Panniers
They come in various materials. Some are lighter and easier to roll up behind the cantle, others are made of Iron Cloth and very tough but are somewhat bulky when rolled up. The lighter ones are easier to roll up and tie on behind a cantle , but when loaded and the brushes against a tree or rock they can tear. The heavier fabric panniers are much more durable to abuse the horses will give it.
When packing, Make sure you even the load on both sides. That is really easy to do with two bags of feed. Since each bag weighs the same. If you put a 80lbs bag on one side, You need to put 80lbs of gear on the opposite side. And yes I've been know to place a couple of rocks in the panniers on the opposite side to even out the weight. It is much more important to be even , than a few extra pounds.
Hay cubes and pellets work fine. 10 lbs of cubes is = to 10 lbs of hay. The big challenge is getting them inside the horses. When camping, you don't have mangers or buckets with you, So you are often pouring the hay cubes on the ground. And you will loose some. Mashed into the dirt or pee'd on. I often feed the smaller pellets ( rabbit pellet size) in nose bags to prevent as much waste on the mountain. Or place the cubes on old feed bags on that I put on the ground.
I also bring hobbles and let my horses graze what they can find. The pellets or cubes make sure the horses are getting the calories they need, But the grazing on yellow grass satisfies their urge to chew and the longer fibers help fill them up. Even if there isn't much nutrition in dry yellow grass.
Offer water and the horses will consume what they need .
Your pack horses should be able to carry 150-180 lbs of supplies very easily. Dead weight is harder to carry than live weight. Meaning that you as a live person who works at keeping your balance is easier to carry than bags of feed or other supplies that make no effort to help balance.
I often use a Top pack. These packs sit ontop of the panniers. Basically spanning both sides of the horse. These are great for lighter items. Sleeping bags, cloths, etc. I just stuff them and throw them on top and tie everything down.
I did see all that info when I went looking about saddle panniers. Thank you :)
I am trying to research early.. the trip isn't until June-ish, so we have time. I do want to also work on hobbling more, but probably won't be doing it, as the majority of the area we will be in is fairly rocky, and that worries me with hobbles. I do plan on letting them graze in hand, or even during breaks while riding. If the ground is better then, great, they can hobble as well. :)
We will have corrals to keep them in. I was thinking I would just hang an empty bucket from the saddles (one on each side, of course!) for the water... not sure on the cube eating, the empty bag is a good idea. My husband was talking about feeding only pellet grain while we are there, as it is easier to pack in, in regards to its space to weight ratio. That worries me, in regards to such a large diet change for them, as they really don't get any grain during the summer, just a bit a few days per week to give vitamins.
My hope is that the horses will really only have to carry their hay/cube and some water. We will have our stuff on our backs in packs, and the dogs will carry their own food and some water in as well (they are larger dogs, so this has always been easy). We plan on dehydrated food for us, and the cabin we are going to has a stove, cots, pots, etc. So that really cuts down on stuff to carry.
In reality it is near full amenity cabin camping with an outhouse, but you can't get a horse trailer closer than 3 miles, so you pack in food, water and clothes.
There is also supposed to be a stream I am going to ask about, so that hopefully means water won't be as much of an issue, because we can filter for us and they can drink it straight.
Thanks for all your info, it really helps!