I got 2 F&W Runners and one especially seems to have "weak" legs.What I mean is, at first I thought it was cold all the time but now I'm thinking it's legs look a little thinner than the others. What should I be doing for this? I have the duckling on vit/electrolyte in the drinking water...gets enough exercise and has from the beginning.The runners are 5 weeks old.When i first noticed it I started the vitamin water and I think it's helping. Any ideas?