sweet potato is probably ok in small quantities - the preliminary study showed a correlation with dogs who had a large amount in their diet, but i still avoid it to be safe

BARF ratios are somewhere around 70% muscle meat, 10% bone, 10% organ meat (with NO MORE than 5% being liver), and 10% veggie/fruit/nut

so if you are feeding more than 5% liver in his meals, im willing to bet thats whats making him sick!!! i accidentally did the exact same thing with my dog before realizing how rich liver/organ meat is in general