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My Sophie never was a picky eater but I still wanted the most nutrition in her diet. I feed her Wellness, an all natural small breed dry kibble and she likes it. I have read here on YT that some feed their picky eaters or sick dogs cooked chicken but if he hasn't many teeth I don't know if he could digest it. You can get more diet information on the health & diet forum here at YT. Your vet should be able to tell you Jax approximate age by his teeth. Good Luck and I hope he's feeling better soon.