I've been raising my Cornish X chickens for just over 5 weeks now, and last week I did such a dumb thing that I'm only just now willing to talk about it.
I had been so impressed with my birds! After the first couple days with losses, they were doing so well! I had 21 left (from an original 25), and they were all so healthy, and the amount of food they were eating each day kept increasing. I'd check on them every couple of hours, and when the feeder was empty I'd refill it.
Then one day their eating just plateaued. They weren't emptying the feeder. They'd eat about half of it and stop. And no matter how long I left it they'd ignore it and not finish it. They had gone from eating their feeder empty twice a day to not emptying it at all.
I let it go on like that for about 5 days, giving them a full feeder in the morning and nothing else because they weren't eating it all anyway. They stopped growing. They weren't drinking as much. I was about to come here for advice when I decided to try fermented foods first, since I had wanted to anyway. I fermented some feed and filled the feeder and watched them go at it. As they ate it down to about the level at which they stopped eating the regular food, since I was still watching, I was able to SEE - they did not stop because they were no longer hungry, they stopped because their heads could no longer fit any further into the chick-sized holes in the feeder!!!
I felt SO horrible. I couldn't believe that had not dawned on me before. I immediately snatched the feeder out of the pen and flipped off the part that keeps chicks from walking in the food, and put it back. They immediately devoured the whole container of food, and two more. It's been six days since that realization, and they are currently eating three full feeders per day, rather than just half of one. Their growth is definately impacted. They are gaining weight and size again, but they're not as large as they should be at this age. I don't know if it will recover.
I'm relieved that they still seem to be healthy. They never appeared sick or slow because of not getting enough food. None of them died. But I still feel bad about it.
Anyhow, I hope someone else can learn from this mistake, and keep an eye on their chicks' abilities to reach the food they need to eat, and to think of causes like that if they experience a lack of growth. Some things are just dumb human mistakes.