Protein level depends on the breed, many wild species need it way higher, but I am sure we're talking domestics here right? For them 15-20% is perfect. I have also used medicated feed on many many breeds domestic and wild, and absolutely no problems with it.
Everybody says not to though?? Not sure why, doesnt seem to hurt any of mine... Mine is medicated with amprolium for coccidia.
I have had better luck with the medicated chick starter-grower with my ducks than the non-medicated. I used the medicated with the first 15 I ordered from murray and they all lived and thrived well, I didn't use it with the last 15 I ordered and I lost 6 in the first week so I do beleive that even tho they tell u at the feed store's not to use it on ducks it is the best to use . And at around two weeks add a container of peas in there and let em eat those and also I gave mine spinach they loved it!!!!