My guess is that it is because your aunt fed Toby some of the old food. We switched Eva to Orijen weeks ago and her light loose poopies are now nice dark brown firm little links. She was previously eating Nutrience, and wow what a difference once she was completely off of it.
I wonder if teething can cause the same issues though. With kids it can. I wouldn't rule it out. But if you have switched foods it probably is best to keep on one and not mix especially a zero grain food. I bet their bodies get used to not having the grains pretty fast, then if you introduce it again it will upset everything.
He sure is a sweety.
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Mary
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