Southwest Airlines will limit customers to only one dog or cat as an emotional-support animal, changing its policy after a biting incident on a flight.

The carrier follows larger rivals that had altered policies for animals on board as numbers soared for passengers claiming they rely on them. Problems with animals, including a child nipped on a Southwest plane, also have climbed, as have the types of creatures brought on aircraft.

Effective Sept. 17, Southwest will limit emotional-support animals to dogs or cats, and one per person. The animals must remain in a carrier or on a leash, and owners must present a current letter from a medical doctor or licensed mental-health professional on the day of the flight, the Dallas-based airline said in a statement Tuesday.

Beyond emotional-support animals, only dogs, cats and, on occasion, miniature horses will be allowed as psychiatric-support animals, Southwest said. They must be individually trained to perform a task or work for a person with a mental-health disability.

The airline won't allow unusual or exotic animals on board.