The five groups of nutrients that all animals require are proteins, fats, carbohydrates, vitamins, and minerals. Fatty acids are the structural units of fats, and amino acids are the structural units of proteins. Ferrets require a fatty acid (arachidonic acid) and two amino acids (arginine and taurine) that are not found in sufficient quantities in any plant material. A ferret is therefore an obligate carnivore. You cannot feed her a vegetarian diet without endangering her life.
Anatomy of a ferret's digestive tract
Ferrets have a very short, simple intestinal tract. The large intestine and cecum of most animals contain bacteria that digest complex carbohydrates found in vegetables and grains. Ferrets have an especially short large intestine and no cecum. They can digest simple carbohydrates such as sugars and starches, but not the more complex carbohydrates such as those found in beans, bran, and broccoli.
It takes only 3 hours for a morsel of food to be swallowed by a ferret, pass through the digestive tract, and come out in the litter box. This rapid passage time means that digestion of food is inefficient compared to other animals. Some food is passed unchanged from one end of the intestine to another because it is not exposed to the digestive enzymes and the lining of the gut for long enough to be completely absorbed – this applies to complex carbohydrates, like vegetables.
If you want to see how little a ferret's intestine changes the food he eats, feed him dark colored pellets in the morning, then take them away and feed light colored pellets. If you check the litter box in the evening, there will be two different colors of stool, and sometimes the same piece of stool will be divided into light and dark areas.