Trekking with a pack animal is not something to be undertaken lightly. If it is private property the land owner will define requirements and likely provide the animal, usually with a guide/handler.
If it is public property, there are rules that very drastically by location. But in general.
Unlike human visitors, Equines (horses, mules, donkeys, and burros) must have their feet cleaned and be on a special diet several days prior to venturing on to the trails.
Feed: Clean trailers, hooves, coat, mane, and tails prior to entering the park. Feed stock weed-free forage or processed feed a few days before the trip. To prevent introducing non-native plants in the park, use only certified weed-free forage— hay, straw, and mulch. Proof of certification tags required. Forage may not be taken beyond trailheads. Use pelletized feed, hay cubes, and grain products in the backcountry. Do not leave feed on the ground; use a feedbag or tarp. Pack out unused feed. Grazing not permitted. Source
Additionally Equines are only allowed on specific trails.
Where an animal must carry its own food, it quickly becomes problematic for length of adventure. Depending on the animal and the terrain, a pack animal who is only carrying their own food, will have a max range of 5 to 10 days.
Related What is the feed limit for various pack animals?