I have seen several people feed pinky mice to their axolotls once they hit 10 inches. I heard that the bones are very soft so the axolotls can pass them fine, and that as long as you feed them no more than 1 every 3-4 months, they will be fine and it may even be beneficial. A lot of people also said that axolotls should never eat pinky mice or guppies that you raise on your own (I have yet to test that out), about a month ago I fed my axolotls (both 10 inches) a pinky mouse and they ate it happily. I didn't notice anything wrong, so I didn't think much of it. Then today while doing a water change, I went to siphon out some poop and there was a hard thing in it, I took it out and examined it and realized it was the skull of the pinky mouse, it took them over a month to digest them. Don't feed your fish (or axolotl in my case) something that takes that long for them to digest