prey model raw is dependent on the inclusion of secreting organs (liver, et al) for a balanced diet.
Prey Model Guidelines: Feed 2 to 3 percent of your dog's ideal body weight each day, with 80 percent of the diet being muscle meat, 10 percent bone and 10 percent organs. Of the 10 percent organs, 5 percent, half, can be liver.
what are [some] secreting organs?
Liver (in rabbits, pancreas is also [sometimes] included in their liver), Brain, Testicles, Kidney, Spleen, Thymus
Commonly confused as organs, but still in the 'offal' catagory - heart, skin, eyes, stomach (lining), tongue and lungs are considered muscle meat.