Chicken found dead on her side in nesting box, what happened?

[Chicalinga]

Was her comb a purplish color, by chance? That could indicate circulatory issues, like a heart attack.

 

[Jmcintosh23]

Finding a hen dead in a nest box almost always is caused by heart failure due to sudden death syndrome. It's caused by usually two eggs back to back putting extreme demands on her to produce enough calcium for two eggs. This can rob the calcium in her blood to meet this demand and there is therefore none left to supply the needs of her heart for calcium to keep it beating. The hen dies of a heart attack.

How do you know this open her up and examine?

 

[Soujrnr]

We had the same experience a little over a week ago. She never has laid two eggs in one day, and she was doing fine all day. The next morning she was in one of the nesting boxes dead. There was one egg underneath her. It wasn't super hot, but it was definitely hot and muggy. The other chickens didn't seem phased by it at all. They get plenty of water, food, grit, oyster shells, treats, and hours of free range time each day. She was about three. It was sad, but we'll get more. I'm sorry for your loss, too. Ours are pets for us, as well as giving us great eggs each day.

 

[Kiki]

Fatty liver disease kills quick..without any warnings
If your bird drops dead you should send it to your state lab for an answer. The answer could possibly save other birds.

If you don't send it to your state lab for a Necropsy opening the body up yourself can be eye opening...some times.

 

[azygous]

How do you know this open her up and examine?

No, of course I wasn't there and didn't open up the hen after death. But the circumstances of the death had the signs that indicated this was a strong possibility.

The original poster did say they suspected this hen had been having shell quality issues. Therefore, when a hen dies while on the nest, absent all other symptoms, we would strongly suspect heart failure from a sudden draw down of blood calcium while trying to lay an egg.