ToME WikiRavenRed: Quick Idea. As most Yavanna worshippers know, Piety is a ridiculously precious resource, and that the God-school "Charm Animal" spell is rarely effective as a means of raising piety.
What I'd propose is that the spell become a touch-distance spell with no ball effect, which instead of consuming piety, consumes a single food item from the player's inventory. This piece of food need not be a ration, a strip of venison or biscuit would suffice (making these items slightly more than flavour, as it were). If you want an animal to be friends with you, feed it. 
This limits the spell significantly in some ways, with the range, lack of a ball-spell and single-monster focus. But the advantage is that the player has relatively unlimited and non-piety consuming use of the spell. To make it a bit nicer for higher-level druids, at Spell Level 50, it no longer consumes a food item, rendering it zero cost.
Shoob: heck, why not just make feeding animals increase your piety for Yavanna? Then add a hostility rating to an animal, so they don't always take it, and so feeding them does not necessarily make them friendly but less hostile instead, and make it so that certain animals only take certain foods. I can see some people singing "feed the birds" while tossing food rations to the Chaffinches 
btw, that song is in Mary Poppins, if you didnt know...