What is the main ingredient in professor dog biscuits?

It is impossible to tell you the main ingredient in Professor Dog Biscuits without more information. There are many different brands and types of dog biscuits, and "Professor" could refer to a specific brand or just be a generic term.

To help you find the answer, could you please provide more context? For example:

* What brand are you referring to?

* Where did you see or hear about these biscuits?

* Is there any other information you can share about them?

Once you provide more details, I can help you find the answer.