I agree with Taylor...if they are eating the Halo just fine with no signs of allergies or tummy problems..I would just leave it be.
Talking about picking out things. I just noticed this past week, that Mandie (who has always been on Blue Buffalo, but is now on the dog food instead of puppy) is picking out the "life source" bits. Or rather eating everything and leaving those in her bowl. She just started this and I will monitor, but I thought it was funny.