Rhode Island Reds; Weak Legs?

[chicksRcute]

We have 15 RIR. They are now 16 weeks old. We have had three cases of partial disjointment at the knee (two sever (one as a chick, one about 8 weeks), one limping now (unknown case, started yesterday)). Has anyone else found this breed to be prone to leg troubles?

Housing: 8'-0" x 8'-0" x 3'-3" (high) floorless pen, moved every two to four days. Top of 2x4 roosts 22" from ground (edges rounded with rasp, sanded). Hanging feeder (1) and waterier (2).

Comments, tips appreciated.

 

[Eggcessive]

Where did they come from? Are they raised on wire? There could be some genetic bone problems passed on if they are from the same parents. As a whole my pure RIR are very healthy. Most hatchery RIR are more mixed, and should be healthy. Here is a link to read about common leg bone disorders such as slipped tendon, and varus valgus leg deformity:
http://www.thepoultrysite.com/articles/1051/leg-health-in-large-broilers/
http://www.thepoultrysite.com/publications/6/diseases-of-poultry/220/slipped-tendon-perosis/
http://www.thepoultrysite.com/publications/6/diseases-of-poultry/220/slipped-tendon-perosis/

 

[chicksRcute]

We got them from community feed store which was giving the chicks free with a bag of feed. They are not on raised wire. Thanks for the links!

 

[chicksRcute]

We are now trying to free range them during the day. Do you think this will help?