My dog bit a cord. How to boost his immune system for healing?

Hello, and thank you for using Petco Pet Education Center, formerly Petcoach. Oh dear, poor Gus! You did exactly right in bringing him directly to the vet, and I'm relieved that his lungs looked normal as sometimes electrical shock can cause fluid to be retained in the lungs.

In my opinion, there is no specific supplement or medication that will make any significant impact on boosting Gus's immune system - the most important thing is just to make sure he's getting good high quality nutrition, and make sure he stays well hydrated. Since he has burns in his mouth that could influence his willingness to eat, it might help to either offer him canned food (I'd stick with the same brand & type you're currently feeding, to avoid GI upset), or you can soak his kibble in a little warm water for 15 minutes prior to feeding. The extra water in either canned or soaked kibble will also help him stay hydrated. If you need to help entice him to eat, you could add some small fine bits of cooked chicken. I wouldn't advise trying to apply anything topically to those burns, since 1) they're painful and he'd probably resist you touching them, and 2) anything you try to put in his mouth is just going to get immediately licked away. From your description, it sounds like you're doing everything right - I would actually say that the supplement/additive that might best help him heal would be omega 3 / fish oil supplements. Keep up the good work and I hope Gus feels better soon!