I have 2 3 week old Pekin ducks. The one was able to keep up with me really well but recently the smaller one was a little bit behind. A couple days ago I noticed she had trouble getting up and would lean to one side before trying to stand. Then yesterday she struggled to get up at all. She would not use her left foot at all and it would just hang there. She limps on her right leg and gets around by hopping. I noticed that her foot looks bruised, a brownish purple color. I'm not sure if she got hurt running around in the yard. But what should I do? She seems like she's in pain and she wants to keep up the pace with the other duck. Any help would be gladly appreciated.