Often referred to as a superfood not only for humans, this also applies to our dogs! 
 
Vitamin A – a powerful antioxidant. It supports digestion and reproductive organs. 
Vitamin D ­– a vitally important nutrient for immune function. It helps protect against cancers, autoimmune and infectious diseases. It supports muscle and bone strength too. 
Folic acid, B vitamins ­ ­– support mental and nerve health. They help avoid fatigue and prevent anemia.  
Iron – forms hemoglobin, brain function, regulates body temperature. Iron transports oxygen to the blood cells. This increases your dog’s endurance and strength. Lack of iron depletes antibodies and T-cells in the immune system.    
Other minerals (like copper and zinc) – support bone and joint health, skin, coat, immunity.
 
And of course, liver’s a great source of protein that’s also lower in fat than muscle meat.