Police had to be called to the Bury New Road McDonald's in Greater Machester town of Whitefield after the woman's horse left his own form of protest on the restaurant's floor.
"The sight and smell of this caused obvious distress and upset to customers trying to eat, as well as staff members," Whitefield police said in a statement.
Officers who arrived at the scene fined the horse's owner for "causing alarm and distress."
McDonald's has released its own statement confirming the incident, and reiterating its drive-thru policy.
"The health and safety of our customers and staff is our top priority," a company spokesman said, "and for this reason we are unable to serve pedestrians, bicycle riders or customers on horseback through the drive-thru."