Purina Pro Plan Veterinary Diets HA Hydrolyzed Salmon Flavor Dry Dog Food is crafted with 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. This canine kibble is highly digestible and made with high-quality ingredients. And you can have peace of mind knowing that the science behind is all thanks to the collaboration between Purina researchers, nutritionists and veterinarians.