I have lost 8 out of 10 RIR pullets that are just 5 months old. Same symptoms...find them unable to stand, they just fall over on one side. No drainage, no nothing. Also, it seems they are very friendly before they die. No respiratory nothing. My rooster, I found him down and out in the coop about 2 hours ago. I try to get him to stand, won't. I gave him 1 cc pro-pen. I figured it was a repiratory hereditary thing in the 8 as they came from the same place, hatched at the same time. The two that are left are smallish and their legs are scrawny and pale, and their combs are not really in? Not sure if I am dealing with mareks disease or not. I brought the rooster in and checked him for mites, ticks, anything crawling...nothing. They are free range with a nice coop to hang in. 2 feeders and fresh water all the time. They were raised on medicated chick starter and are eating nutrena laying pellets. Ask away with any questions that may help me with this mystery...it is truly a heart break.