When are shelties considered full-sized? 10 months to a year-ish? When she has come close to that is about right.
Because puppy foods do have extra calories, generally, calcium, and various nutrients, they should give pups what they need to grow.
Once upon a time, we didn't leave puppies on puppy food for as long, they were often off of it inside of 6 months, regardless of breed, but research seems to have proven out their worth in building strong bones, etc. At least with the modern puppy foods. They may have improved them over the decades that they've existed.
Also, in your case, Arwen is a smaller than average girl, and the extra boost of the puppy food could help her to get a little closer to what is considered the 'norm' for a sheltie.
Not, mind you, that there's anything wrong with her being smaller than average, she's adorable. But, if it's in her to grow a little more with good nutrition and calories, it might be best for her to do so. (We won't talk about the fact the Dh always jokes that I'd be taller, if I'd had more meat in my lunch sandwiches! lol!)
So, you could change her over as early as 6 months, but I'd recommend going to 10 months to a year, if possible. Unless there's something about shelties that I'm unaware of, of course.
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