How do I figure out how my Cornish X died?

[Mtnmomma3]

I had a six week old Cornish X die on me last night. They free range during the afternoon and when all of the other chicks went back towards the heat lamp and food at dusk, my largest bird was very lethargic and I had to carry him back. I thought about keeping him quarantined but I didn't have a whole other lamp/food situation so I closed the coop and went to bed.

He was belly up this morning. I checked over the ground where the hoop coop sat last night and don't see signs of unusual chicken droppings.

The other chicks seem perfectly chipper, but of course I'm worried that he had something that they could catch.

Any suggestions on solving the mystery or what steps to take when one bird dies? Maybe there are no steps, but having never lost a bird, I don't know about contamination, etc.

 

[Indypurrs]

Chances are it was a heart attack from fluid build up. If you are able I would do an amateur nuerocropsy. Look for fluid in the body cavity extra fat on internal organs.

 

[AmericanMom]

Thursday I went out to feed my meaties and found one of the hens laying in the yard, she was alive but breathing heavily, I knew it was more than likely her heart as this can be a problem with the birds, I took her in the coop and made her comfortable and hoped she would last until hubby got home from work because although I have no issue with knowing these brids are destined for the dinner table the one thing I cannot do is gut them.. I came in and looked it up trying to make myself go take care of her as to not waste a whole bird but I just couldn't do it.. I went out several times that morning and she seemed better, even got up and ate but when I went back at 3pm she was dead... So frustrating and I am determined with the next round we purchase to make myself process a bird on my own.
I can hang them in the cone, I can kill them I can dunk and pluck them but I just cannot gut them...