Cellulase is not an enzyme found in animals. It's primarily found in plants and microorganisms like bacteria and fungi.

Here's why:

* Cellulose is a plant-based polymer: Cellulase breaks down cellulose, a complex carbohydrate that forms the cell walls of plants. Animals don't have cell walls, so they don't need to break down cellulose.

* Ruminants: While some animals like cows and sheep have symbiotic bacteria in their digestive system that produce cellulase, this is not an enzyme produced by the animals themselves.

* Plant defense: Plants produce cellulase to break down cell walls for growth and development.

* Fungal decomposition: Fungi use cellulase to decompose dead plant matter.

So, while animals can benefit from the presence of cellulase, it's not an enzyme that they produce themselves.