From MO1 Forums:
2 skill points in Creature Control give 1 pet point and 4 skill points in Advanced Creature Control give one pet point, so with maximized skills you can reach 100 pet points: 25 base + 50 + 25.

Zoology is needed to reduce the pet points for a pet by 25% with full lore. If a donkey takes 24 pet points without Zoology (and the skill for donkeys), then with full lore the donkey costs 18 pet points.

If you have two pets at the same time, then the pet points are reduced by 20: E.g. 100 pet points with one pet and 80 pet points with two pets. Herding decreases the penalty from 20 to 10, so with full Herding lore and two pets you have 90 pet points.