It can take up to 6 or 8 weeks for all the histamine to clear out of his system from the last reaction, but you can usually tell within days that he is starting to get better. It depends on how strongly he reacts to a food how long it will take to see a reaction. It looks like he reacts strongly to rice and showed a reaction pretty quickly, other things could take days.
NVI LID is a good starting point to try to work this out. Has he ever had a lamb food before? You usually want to start with a protein and starch source that he has never had before and feed it for 6 to 8 weeks to clear all the histamines out of the body. Then start adding back one single ingredient for a few days to see if he reacts to it. If he has a reaction, then go back to what you know worked until the histamine clears again and then start again. Keep records of what you tried. Keep ingredient lists of foods that worked for him and foods that don’t, so you can try to figure out what ingredients in those foods were the trigger.
I’ve been going through this with my dog for a year and a half now and finally have 3 different kibbles he does well on. Now that I have a handle on his triggers, he lives a pretty normal life.
