I think sometimes cats can be picky about the food texture. NV medallions were sometimes hit and miss with my two cats. They preferred chunkier meats than the finely ground up that NV offered, so I stuck to my local brand later on. I haven't tried Primal's version, but most times I offered commercial raw, I've had no issues with loose stools. No issues with changing different proteins with different brands, as long as it's a good and balanced mix. It seems it's just G's picky nature about texture is the biggest hurdle with my cat.
To get the kitties to try a new brand, I'd use a small serving of their favorite freeze dried treat as toppers or used a bit of their favorite canned food as a "gravy" after diluting it a bit of water. You could also add probiotics in the gravy at this time, to make food transitions easier on their tummies. Unless the new commercial raw has a lot more organ meats, it shouldn't cause to much problems. If they do get a bit of loose stools, you could alternate rabbit meat (with higher bone content) later in the day as a meal to help balance things, too.
The only times I've had issues with loose stools is when they get a chunk of kidney or liver (since doing PMR), but that is easily remedied with a bit of bone added back in.
Last edited by TabbCatt; 10-15-2015 at 02:59 PM.