Furious Inhalation( Races of the Dragon, p. 102)
While raging, you can use your breath weapon to deal energy damage with your bite attacks.
CON 13, ability to rage or frenzy, bite attack, breath weapon, Dragonblood subtype,
When you enter a rage or frenzy, you can channel one use of your breath weapon inward to add energy damage to your bite attacks. Activating this ability is a free action; the effect lasts until your rage ends or until you use your breath weapon again. While this feat is in effect, your bite attacks deal an extra 2d6 points of energy damage, matching the energy type of your breath weapon. If your breath weapon doesn't deal energy damage, this damage is fire damage.