Have you diagnosed any allergies by skin or blood tests?
Purina HA starts off with corn starch as the main ingredient.
http://www.allivet.com/Purina-Canine-HA-Hy...ula-p/26996.htmDr. Alan Ebringer in the UK has determined that Crohn's disease is caused by overgrowth by Klebsiella pneumoniae (Kp), and that feeding starch to people with Crohn's (and ankylosing spondylitis) is contraindicated. Not that your pup has Crohn's, but if IBD/PLE is the same in the hound, this means:
1) Feeding high-carb food is what probably caused this disorder
2) Feeding starch is the LAST thing you want to do
But- I offer no guarantees that your pup has Kp infection. It's a simple perianal swab followed by culture on MacConkey agar to find out. To the best of my knowledge, this has not been explored in the canine. Of course, it may not be Kp, and could be one of a number of organisms that do well on carbohydrates.
My advice would be to feed raw food. If that is not feasible, then a bagged kibble that is as low in carbohydrates and entirely lacking starch is strongly recommended. There is absolutely no nutritional requirement for carbohydrate in the canine; of the three macronutrients (fats, proteins, carbohydrates), only fats and proteins are required. The feeding of polymeric carbohydrates (mainly starches as found in grains) to the canine could be the cause of bacterial overgrowth in the gut, as these are not well-digested, and serve to feed bacteria in the intestines. This leads to damage, and then PLE, diarrhea, and other malabsorption.