My 13 week old chicks are dying

[Birdie2019]

No they did not get layer ration at 8 weeks. Only in the last couple weeks (11 weeks) and it is organic layer ration, but they have still been eating the medicated chick feed mostly.
I already took one to the vet and he couldn't figure out why they would not be gaining weight. No eye infections, the poop was normal. They were just as stumped.

Okay. You think it could be Marek’s? I know that’s something that lots of people jump to, but look at these symptoms-> https://thepoultrysite.com/disease-guide/mareks-disease
Not all of it is totally true, but some is at least.

 

[Folly's place]

I'm so sorry!
Any herbicides or pesticides used where they are? Mites or lice? Look at the birds at night, while roosting, with a flashlight. Look at the skin around the vent, under wings, on back and neck.
Have necropsies done! If you are in the USA, your state veterinary lab can do this. Wrap a fresh body in plastic, refrigerate, and get it there, after calling ahead.
Mary

 

[Wyorp Rock]

No diagnosis. He said he felt a mass in it's abdomen, but she was still pooping. No tests were done - she was euthanized at the vet.
How long have they been in the coop/run? For about 3-4 weeks.
Definitely wasting! They don't even seem to have anything in their crop - like they haven't even eaten, but I've seen them eating a lot. That's why I'm confused. They get lethargic and unsteady a day before they pass. It's very upsetting.

No they did not get layer ration at 8 weeks. Only in the last couple weeks (11 weeks) and it is organic layer ration, but they have still been eating the medicated chick feed mostly.

The vet thought it was almost like a gastric/intestinal blockage

If possible, have your vet perform a fecal float to check for Coccidia load.
Are you providing a source of grit?
Photos of poop may be helpful.

Since they have been in the coop about 3-4 weeks, they may have Coccidiosis. Your vet will need to provide you with medication since you are in Canada.

I would not feed 11 week old chicks layer feed - makes no difference if it's organic or not - the calcium content in layer feed is too high for chicks. Use chick starter or an all flock type feed that has 18-20% protein until they all come into lay.