I'd suggest:
+50 hunger (Considered a fine dish, Warly will not get a penalty for eating it, and will get 33% more health, hunger and sanity from it)
+20 health
+15 sanity
Truffles have to be plucked, so pigs can't just eat them off of the ground (unless you put them there)
If a Truffle is fed to a Pig, they will become better friends with you. They will say certain new quotes when you're nearby, and you can trade certain items with them in exchange for meat (determined by crock pot values). Each day they'd have a different selection of items, and I'd suggest these could be some:
(Values are based on how much you'd get from 1 meat, so if you gave them a morsel, you'd gain half of the items. No idea how balanced these would be)
Rot x 2 (Common)
Log x 20 (Common)
Flint x 8 (Common)
Silk x 4 (Common)
Grass Tuft x 1 (Uncommon)
Sapling x 1 (Uncommon)
Berry Bush x 1 (Uncommon)
Gold Nugget x 4 (Uncommon)
Nitre x 4 (Uncommon)
Blue Gem x 0.5 (Rare, 0.5 means it requires 2 meats in order to purchase)
Red Gem x 0.5 (Rare)
Thulecite Fragment x 1 (Very Rare)
Purple Gem x 0.25 (Very Rare, 0.25 means it requires 4 meats in order to purchase)
Orange Gem x 0.25 (Extremely Rare)
Yellow Gem x 0.25 (Extremely Rare)
Green Gem x 0.25 (Extremely Rare)
Again, forgive me if these are unbalanced. I'm no expert at balancing resources. You'd be able to buy certain otherwise non-renewable resources (thus, making them renewable). Pigs would also have a "Friendship Meter". This will go down over time, but if you do certain actions, you can affect it. Giving them free meat would increase it depending on the meat's hunger value. Trading meats with them would increase it depending on the hunger value (but less than giving it free). Truffles would increase it by a lot, giving them Monster Meat would temporarily increase it, but it will be decreased after the next day. If it gets too low, you won't be able to trade with them anymore, and you will need another truffle. When it's high, you have a bigger chance of getting rarer items, and you may get certain offers on items. Also, if you recruit a pig using meat, the duration of the effect will be increased.