Hey Beaucollie!
I agree with mackenzie11, I've never heard of that before. My puppy is 7 months and is still on his puppy food as it is full of all that "goodness" for his growth etc. At 12 weeks I would think you should definitely stick with puppy specific foods as it is also a lot gentler on their stomachs. I'm planning on sticking with large breed puppy food until Bosco is around 12months
Maybe if there's any other collie owners out there who could suggest what they're feeding??
BB