Goldens4Ever, it might be the beef. It's "common knowledge" that dogs are prone to beef allergies, but it's not as big a culprit as chicken is now, IMO. It all depends on what foods they got before. Less foods are beef based (other than the super cheap ones and a few holistic ones) and it seems more companies have moved to poultry.
Worrier, it wouldn't hurt to try the chicken Canidae... Maybe get a sample if you can.