why does herbivores animals have bigger intestine than carnivores animals?
Carnivores have a shorter intestinal tract because they process the protein quickly and eliminate it. Herbivores have the longest intestinal track (some have multiple stomachs) do to the complexity involved in digesting cellulose, fiber, grains and plants. It takes longer for these to break down and for nutrients to absorb. Humans digestive tract is much shorter then an herbivore- we are made to digest protein (hence why we don't produce all the essential amino acids), fats, simple plants (vegetables and fruits)
Herbivores that longer intestines than carnivores to digest grass. These intestines would host many small bacteria that processes and breaks down cellulose intoglucose, a source of energy that the host herbivore can use. Without these long intestines, animals such as cows could still eat grass, but would not be able to use the glucose stored in the grass structure.