Purina Pro Plan Veterinary Diets HA Hydrolyzed Canine Formulas contains hydrolyzed protein, which is protein that has been broken down into small components to be less likely to cause an adverse food reaction in certain dogs. HA Hydrolyzed is highly digestible and made with high-quality ingredients. The science behind our therapeutic diets represents a collaboration between Purina nutritionists, researchers and veterinarians.