Had the same thing and asked the pedi at one of our earlier app'ts. Comes from DC getting more fore-milk - it creates the green pesto colored poop. Normal. It's gone away as DS has gotten older and has consistently longer feedings.
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Assuming it is not also frothy, I was told that it happens when the baby gets a lot of foremilk, but not the hindmilk. ?Is he finishing each breast at the feeding? ?
DD WAS sick (well, she had 4 weeks of diarrhea) & hers was green. The pedi said the green was bile. We looked it up & we found that all poop starts out green & the longer it's in the intestines it starts to turn brown, so for us it was green because it was going through her too fast. I've also heard it can be a hindmilk/foremilk imbalance, though - too much foremilk, which has lactose, and it's too much for their intestines to digest at once so it "flies" through the intestines before it's broken down all the way.
i researched this the other day on the internet. I think I remember seeing green stools could mean virus. Search for green infant poop or something like that. I found a list of all the different descriptions of baby poop and what is normal and what the different colors mean. Sorry I dont remember where but I did search something similar.
Re: BF question - green stools.