Help my chickens are dying

[karenpalmer]

we have had three successfully laying flocks of chickens over the past four years. We know about deworming chickens, including grit in their diet as well as a source of calcium for strong shells. We have only two remaining hens from a flock we started last March 2016. Today I found the third hen dead inside of the hen house. All three have appeared to be healthy immediately prior to finding them. They were laying, eating, and drinking. No lethargy or sudden weight loss. In fact the one I just found was walking around and tried to peck my son who was changing their water out just yesterday. I have not changed ANY factors with our feed, watering or bedding. They have died months apart
from each other too. So if it was a virus/bacteria I assume it would kill them closer together, right? I did not inspect the bodies but there doesn't look like any trauma occurred, or foul smell from them.
Help!!! I only have two left. And I am certain they are both healthy layers.

 

[coach723]

If you still have the body you can refrigerate it and send it for necropsy. Necropsy is really the only way to know for sure what happened. It is not uncommon to have a string of losses that are completely unrelated, but the only way to know for sure is to necropsy them. There are many, many possibilities.
Here are some lab resources by state: https://www.aphis.usda.gov/animal_health/nahln/downloads/all_nahln_lab_list.pdf
http://www.metzerfarms.com/PoultryLabs.cfm
You can also do a basic necropsy yourself, but you will not have lab results in the event it's viral or bacterial or find no obvious abnormalities. If you choose to do one yourself you can post pictures here and ask for opinions of those who are familiar with them, just title your thread with the info/warning that it's a necropsy with graphic photos.
Here is one link with info on how to do your own if you want to do that, it does contain graphic photos: http://naturalchickenkeeping.blogspot.com/2013/11/how-to-perform-necropsy-autopsy-on.html
I'm sorry for your loss.