Two of my 7 silkie 8-week-old pullets are loosing their ability to stand, walk and sit up. It started with being uncoordinated in walking and quickly progressed to spraddled feet, then eventually they couldn't even hold themselves up. They are on the medicated starter feed, vitamins/minerals that I add to the water and ACV. They have free access to crushed oyster shells for calcium and chick crushed grit. I'm at a loss. I have brought them in the house so I can make sure they get food and water throughout the day. Any ideas? Vitamin B? Riboflavin? The other 5 pullets are happily running around the coop with the adults. I certainly don't want the rest to go this way. I'd appreciate any ideas on this.