Training a horse for packing is fundamentally a desensitization process — the horse must become completely comfortable with the appearance, sound, smell, and feel of packing equipment, loaded panniers, the motion of loads against its sides, and the range of unexpected situations it will encounter in the backcountry. A horse that accepts a saddle readily may still be completely unprepared for the additional sensory experience of a loaded pack saddle with panniers swinging and clanking against its sides.
The process begins on the ground with progressive introduction of the equipment. The pack saddle pad, then the pack saddle itself, then an empty cinch, then a lightly loaded pack saddle — each step is introduced only after the horse is fully relaxed with the previous step. The noise of panniers rattling and bumping must be introduced carefully and incrementally, because it is often the noise rather than the weight that initially worries horses.
Once the horse accepts a loaded pack saddle calmly at rest, it is walked — first in a controlled environment, then in progressively more challenging terrain — while the packer monitors the animal's response. Trail exposure before the first serious packing trip is essential: the horse should have experienced stream crossings, downed timber, steep terrain, and encounters with other pack animals before being asked to handle those challenges while also managing a load.