Limpy Gimpy Pekins

I have 3 pekins about 4 years old.  My first trip to the vet cost me $700 to repair a suspected racoon bite to my Pekin's foot--visits, xrays, bandages, and medication. 

I have a second  Pekin that gets around ok, but she just started limping about 4 months ago, having no visible signs of an injury or infection (no trip to the vet). 

My 3rd duck is so lame, she only travels when she has to.  I really watch out for her by putting her in the pool , taking her out, and setting her close by food and water during the day (she is in a pen at night).  All of the ducks  appear healthy with no visible infections or signs of pain (but then how would i know if they are in pain). 

Do pekins tend to have foot issues?  Arthritus issues? If so, is it because they are a heavier duck? 

Their food is a mix of Nutrena gamebird pellets and Layena egg laying pellets (as one hen is still laying).  They also get extra calcium and B supplements.  The majority of the day, they forage our clover yard for bugs and greens.

They forage  on 3/4 acres of  clover; back 1/2 area dries out in summer &  front 1/2  keept green.

Weight...They are free foragers and are supplemented with  2 feedings a day.  Not sure what they weigh (or how much they should). 

I will investigate this and, if they are overweight, put them in their pens a few hours to decrease their in-take.  This may reduce the weight, ease the leg pressure, and limping. 

Thanks for the feed back.  I bet it is there weight!