I have 13 chicks in a 100 gallon cow trough with pine bedding. All of the chicks are from the same clutch, hatched three weeks ago, in ,my incubator, from my hens. This morning I went to feed and water everyone and three of the chicks were dead. They were laying in the middle of coop with no signs of distress (nothing had gotten into the trough). Two of the chicks showed no signs of physical ailment, but one had a drop of very dark, runny stool on its wing.
I found this puddle of bloody stool near one of the other chicks
Yesterday evening we had them out playing under this apple tree for a few hours. We've been taking them to this location daily since they were a week old. I don't see anything that could have caused them a problem
There are only two budding plants anywhere near the tree, so I've posted pics of the plants and buds in case they may be the culprit
I only feed Layena pellets and have seen no signs of trouble from any other chicks...these were fine when we put them back up last night. Please tell me what I've done wrong.

I found this puddle of bloody stool near one of the other chicks

Yesterday evening we had them out playing under this apple tree for a few hours. We've been taking them to this location daily since they were a week old. I don't see anything that could have caused them a problem

There are only two budding plants anywhere near the tree, so I've posted pics of the plants and buds in case they may be the culprit



I only feed Layena pellets and have seen no signs of trouble from any other chicks...these were fine when we put them back up last night. Please tell me what I've done wrong.