We feed our dog THK and it was just the opposite, he had gastrotitis was throwing up on the turkey formula but was fine with the chicken one. The vet did a battery of tests and said it was probable food allergy. He's been fine since.
I'm looking up the ingredients for the THK. Preference seems to be the only formula without faxseeds and you have to add your own protein of choice.
I hope Ava gets better soon.
