I mean I could but I have a nearly limitless supply of rabbits in my yard. Their fur makes great gifts. My plants love the compost I get from everything else. As a bonus the blood compost deters rabbits from eating my cabbage.
Funny thing, I can’t seem to find any type of vegan certification that is concerned with the use of animal byproducts or waste in fertilizer. A few specifically say they do not check fertilizer.
My grandfather worked in a lab at a brewery. His job was to sample grain coming in. Rejected grain cars were sent to the cereal factories.