A pet with Chivalry or most any magic will lose mana very fast. So you Max the Mana Regen and put intel to 370 when possible. Pets rely on Mana Regen.
Intelligence increases mana regen but it is not worth putting it above 370 because you can not max the Dex or Str if you do. Mana Regen is more effective than Intel, but put intel to 370 as part of your base build.
If you are doing a short encounter you could use a pet with a lot of Mana. Some players have 1500 mana on their roof pets. They fight each boss then let the pet regen back up.
If you are fighting for any length of time 3+ minutes it does not matter how much mana the pet began with, it is below 100 by now. So the pet is relying on Mana regen for spells and specials.
The pet type determines what amount of mana you can afford.
I do not put HP above 600 on pets anymore unless the pet type has a lot of spare points. So if needed I can add more mana.
But in general I put 400 to 600 Mana on a pet that has points for it.
For pets that do not have enough build points to add Mana I use as little as possible.
My Dreadmare and Wildfire Ostard:
Points are more valuable in something other than Mana when you are short on points.