Whether you are packing a string of mules or loading your Western Saddle Bags, balancing your load is crucial. A balanced load will help protect stock from soring and muscle strain. They will also be more comfortable, which will help ensure their endurance and performance on the trail. Uncomfortable stock can act up. Indeed, a common cause of a wreck on the trail is the shifting of an unbalanced load.
Balancing a pack load
I have seen experienced packers who could load a sheet of plywood on one side and an anvil on the other and hardly ever look back. However, the average packer should not attempt to pack such a load. I stress to my beginning packing students that equal weight, equal size and equal weight distribution are the keys to making your load ride well all day. When using horse panniers, pack each pannier so that the weight is distributed equally across the pannier. Pack them so that they weigh within a pound of each other. Whenever possible or appropriate, I write the weight on each individual piece to help me put my loads together; it helps immensely when reloading at camp.
Hang the horse panniers on the pack saddle so that they ride as high as possible, such that the tops of the pack panniers are at least level if not tipping inward toward the pack animal's spine. This gets the weight up toward the top of the ribcage on the animal where it rides the best. Low hanging weight will cause discomfort and wear the animal out. However, weight loaded too high will cause your pack saddle to be top heavy and prone to shifting sideways, even to the point of sliding around the animal. Remember that top packs are for lightweight, bulky items such as duffels, sleeping bags, roll up camp furniture and some tents.
Lastly, conformation can be a factor in how well your load rides. For instance, a low withered animal will need to be packed more carefully and more evenly as even a minor difference from one side to the other can cause that saddle to shift. At best this is an inconvenience requiring regular adjustments as you head down the trail. At worst, the saddle could shift and slide completely around, causing a wreck with all but the best pack animals.
Most of the time, packing a load successfully requires more common sense than anything else. Think carefully about what you are doing and watch your loads. If you are having problems, get off and adjust right away, repacking if necessary. It only takes a second for a wreck to happen.