Sorry for your loss... If you live in the US many States offer a free or low cost necropsy service.
Many labs listed here:
http://www.aphis.usda.gov/animal_health/nahln/downloads/all_nahln_lab_list.pdf
If your your state isn't listed just let me know and I'll find it for you.
Shipping to necropsy:
https://www.backyardchickens.com/t/799747/how-to-send-a-bird-for-a-necropsy-pictures
-Kathy
Many labs listed here:
http://www.aphis.usda.gov/animal_health/nahln/downloads/all_nahln_lab_list.pdf
If your your state isn't listed just let me know and I'll find it for you.
Shipping to necropsy:
https://www.backyardchickens.com/t/799747/how-to-send-a-bird-for-a-necropsy-pictures
-Kathy