Everywhere I look says to supplement your ducks' feed with niacin, but what if I feed them specialized duck feed? Do I need to add anything if I feed them Purina Pelleted Duck Feed (https://www.tractorsupply.com/tsc/product/purina-duck-feed-pellets-40-lb-3004428-205) ? They will also have access to grass and bugs and whatever else is in the yard. Thanks!