Fecal transplants must use human poop—specifically, poop from carefully screened, healthy human donors. Here’s why:

Microbiome compatibility: The human gut microbiome is species-specific. Animal microbiomes are often very different and might not colonize the human gut effectively—or safely.

Pathogen risk: Using non-human feces could introduce dangerous pathogens, parasites, or other harmful organisms that are foreign to the human body.

Regulation and safety: Fecal microbiota transplantation (FMT) is regulated (e.g., by the FDA in the U.S.) and must meet specific safety standards, which only apply to human donor material.