I started Bonnie straight onto Natural Instinct Puppy food on day one of having her at 8 weeks old. She had been weened onto Beta. She has never had a day's runny tummy and has never looked back. I didn't introduce it gradually either. I wish I had done the same with Dexter as I struggled with getting him to eat at all and he was underweight for a while but I was anxious about changing to a new food too quickly. It also took me several attempts to find him a suitable food. Bonnie also has a chicken wing a day which she absolutely adores.