Sudden Death With No Prior Signs Of Distress

[SuburbanFlock]

First I would like to start out by saying I am new to the forum "just joined" and I hope I have found the right location to post my question. Up until the other day I had three happy healthy RIRs. They where all just about eleven months old and I had raised them from chicks.
My daily routine currently is to open the coop and insure my water is not frozen, everything was fine all three hens out and about. later that day when it came time to lock the coop up I noticed one Hen laying on the floor of the coupe, unfortunately this hen had passed sometime during the day as it was completely stiff. I picked up the Hen and completely looked her over, no signs of attack no blood, I looked all throughout the feathers no mites or any visual signs of a cause of death.
I guess my question is could a young Hen who had been laying frequently, just suddenly die, or is there something I am missing, and should I have concern for the two other Hens who appear to be fine. My coupe and fenced / covered run where constructed just for these chickens, and I have been doing regular cleaning of the floor bedding and poop shelf weekly. Floor is pine shavings that I scoop out and top off with more shavings and some DE. I completely clean this bedding out when it gets two dirty. My poop shelf is really a big liter box full of granular PDZ that is emptied weekly. And my run was grass but now is dirt or mud depending on weather conditions.
Sad to see my first chicken just suddenly die and wondering if there is something I am missing or overlooking.

 

[sourland]

sorry for the circumstances. Sometimes they just die. As long as she and the others were eating and drinking and acting normal, I would chalk the death up to a congenital problem or perhaps a heart attack. Good luck with the remaining birds.

 

[SuburbanFlock]

I appreciate the response, they definitely where eating going through a fifty pound bag of pellets in a little over a month, and water is a five gallon bucket with nipples and a heater cleaned weekly as well. On extra cold days I would put water in a bowl about three or four times a day as the nipples froze solid. Now I got a good size coupe with only two Hens. Not sure if I am ready for more just yet, was planning on growing the flock when weather turns more consistent and warm. Would love to find some local birds around the same age to join the flock, chicks where a blast but allot of work as well. Thanks Again.