There is some truth to this. Psilocybin (AKA "magic mushrooms") grow on cow dung, and is sometimes referred to as "caca de vaca"

On Saturday, April 2, 2016 at 12:00:54 AM UTC-4, Tom Kelley #711 wrote:
Recent research findings from independent groups in University of
Bristol and Sage college in Troy, NY, show cow dung to be an excellent
mood enhancing agent. Cow dung contains a bacteria Mycobacterium
vaccae, which activates a group of neurons in the brain that produce
serotonin - a neurotransmitter that contributes to feelings of well
being and happiness.
So the next time you land out or feel depressed try
finding some fresh cow dung and get a lungful of this fresh fragrance.........

Best. #711.