Hi There,
Back in 2007 we got a little rescue kitten, about 21 days old, very late on a Friday night. As it was so late we gave him the only milk we had, which was human whole milk. Then on Saturday morning we took him for a check-up at the vet and got given some kitten (small animal) milk formula as it is better constituted for animals (e.g. some kittens can’t handle lactose in the human milk).
I made a note on his progress. We got Finlay, as we called him, on the Friday 25th May, and at 4am on Monday, the 28th, he did his first poo! As I didn’t write down anything about colour I think it was good and normal. He did another one at 2pm that day. So he poo’d about 3 days after we got him.
On the Wed 30th he had a little solid food (he sounds a bit older than yours).
On the Friday 1st he’d had a lot of diarrhea problems overnight, so the vet put him back onto milk, gave him antibiotics, and 24 hours of electolites. He was still a bouncy little guy. Sunday 3rd he poo’d a small normal poo, then over the next couple of days his poo was a bit yellow and mixed. The vet had me move his worming schedule up in case he’d got a protozoic parasite from his Mom. We re-introduced solid food slowly.
After all that… Finn grew up to be a healthy strong lovely boycat, who thought I was his Mom and loved to suckle my finger or try to suckle my neck!
Unfortunately he’s no longer with us, having not been able to recover from an accident he had. But he was a lovely little strong guy!
I hope that this helps. I would recommend checking with a vet, especially regarding the milk formula.
I wish you all the luck with your guy.