We fed our kittens whiskas and it went right through them and gave one blood in his poo

We've started to feed them raw now, which I'm trying to suppliment with some wet to make sure they get enough taurine etc. So far our kittens have taken to it very well and have eaten everything we've given them. They seem to really love liver and we also gave them some heart over christmas which went down well. They can't eat bone yet though as they just seemed confused when I gave them a whole chicken wing the other day and decided to try and hunt it instead. I think they're still too small