Animals follow the same rules for encumbrance as humans.
Pony
A light load for a pony is up to 100 pounds, a medium load is 101–200 pounds, and a heavy load is 201–300 pounds. A pony can drag 1,500 pounds.
For a light horse, a heavy load is 690 pounds, a medium load is 460 pounds, and a light load is 228 pounds. A light horse can drag 3,450 pounds.
For a heavy horse, a heavy load is 1200 pounds, a medium load is 800 pounds, and a light load is 400 pounds. A light horse can drag 6,000 pounds.
A pack horse would probably be a heavy horse, something like a Clydesdale or other big draft horse. It's not terribly realistic to have that be a pack animal, as the big horses like that were usually used as warhorses, but it's workable for game purposes.
A heavy horse is a Strength 20 large quadruped. Checking the carrying capacity rules, we see that a Strength 20 normally has a load of 133/266/400 (for light, medium, and heavy loads). A quadruped multiplies this value by x3, and a Large creature by x2. Using the normal Pathfinder multiplication rules, this totals out to x4 (you increase the highest multiplier by one less than the next multiplier, so x3 and x2 becomes x4).
A heavy draft horse would have a light load at up to 532 pounds, a medium load at up to 1064 pounds, and would max out its heavy load at 1600 pounds.
A big horse is strong.
A heavy horse is a Strength 20 large quadruped. Checking the carrying capacity rules, we see that a Strength 20 normally has a load of 133/266/400 (for light, medium, and heavy loads). A quadruped multiplies this value by x3, and a Large creature by x2. Using the normal Pathfinder multiplication rules, this totals out to x4 (you increase the highest multiplier by one less than the next multiplier, so x3 and x2 becomes x4).
Incorrect. You don't apply both modifiers. Both bipeds and quadrupeds each have their own multipliers based on size. A large quadruped multiplies the numbers by 3, not by 4.
Bigger and Smaller Creatures: The figures on Table: Carrying Capacity are for Medium bipedal creatures. A larger bipedal creature can carry more weight depending on its size category, as follows: Large ×2, Huge ×4, Gargantuan ×8, Colossal ×16. A smaller creature can carry less weight depending on its size category, as follows: Small ×3/4, Tiny ×1/2, Diminutive ×1/4, Fine ×1/8.
Quadrupeds can carry heavier loads than bipeds can. Multiply the values corresponding to the creature's Strength score from Table: Carrying Capacity by the appropriate modifier, as follows: Fine ×1/4, Diminutive ×1/2, Tiny ×3/4, Small ×1, Medium ×1-1/2, Large ×3, Huge ×6, Gargantuan ×12, Colossal ×24.
Incorrect. You don't apply both modifiers. Both bipeds and quadrupeds each have their own multipliers based on size. A large quadruped multiplies the numbers by 3, not by 4.
Good point; my mistake.
