psychoology and biologyWatch
Yes, herbivores (like us) lack cellulase; however, since their diet is mainly plant-based, they have developed a symbiotic relationship with cellulose-digesting bacteria that reside in their reticulorumen. These bacteria digest the cellulose for them into smaller absorbable sugars (like Glucose).
Then, just like what happens in humans - Glycogenesis occurs and glucose is converted to glycogen via a series of enzyme-dependent reactions which is then stored in reservoirs in the liver and muscle tissue.
Cellulose > Glucose > Glycogen (A)