I've never used Purina duck pellets, so I can't say anything about it. I have had 2 very qualified avian vets, with lots of experience with ducks, tell me to use Mazuri. I also get my ducks' blood work done at least once yearly. Since switching to Mazuri their health and blood results have improved. Obviously I have a very small sample size, with no control ducks so it could definitely be a coincidence. I also let them forage, and feed them a very small handful each of mealworms a day. They also get small amounts of produce like tomatoes or lettuce as a treat.