Carnivores produce the enzyme cellulase. This enzyme helps in the digestion of cellulose found in the cell walls of plant cells. This efficient digestion of plant material means that carnivores can have shorter intestines.
The cell walls in plants are difficult to digest. For herbivores, the longer intestine provides more opportunity to extract nutrients from plant material.
Carnivores absorb much of thier nutrients from the stomach.
Carnivores do not have to mechanically digest their food.