Have your vet run a bile acids assay on him---it is NOT part of the normal blood work-up. Lots of maltese have liver shunt or MVD & are fussy eaters if this is his case.
I would recommend a probiotic as a supplement. Also in addition to MVD, Maltese can have sensitive stomachs and digestive issues. The food you are feeding him might not be agreeing with him.
A forum community dedicated to Maltese owners and enthusiasts. Come join the discussion about breeding, health, behavior, housing, adopting, care, classifieds, and more!