American Airlines’ updated policy on emotional support and service animals will take effect April 1.

The changes, which specify what kinds of pets and how many can travel on board its aircraft, are the airline’s latest attempt to reign in the surging number of support animals being brought on planes.

Passengers who require service animals will now be able to bring a dog, cat or — in some circumstances — a miniature horse.

Yes, miniature horses.

The Americans with Disabilities Act classifies miniature horses as service animals that should be accommodated where reasonable, forcing airlines to carefully address how to do that within the tight confines of a plane.

American Airlines pushed back against the idea that the horses were suitable for air travel. Miniature horses are classified as livestock, unable to manage their “elimination functions” the way trained dogs can, and pose safety issues like the ability to puncture evacuation slides with their hooves, the airline argued to the Department of Transportation last summer.

Though they’re not as commonly used as service animals as dogs, some people prefer miniature horses because they can live up to 35 years.

Passengers traveling with emotional support animals will now be limited to one dog or cat, and passengers will be required to fill out a veterinary health form before flying that specifies the animal has been vaccinated.

Both service and support animals must be at least 4 months old. Both also fly free in the aircraft’s cabin under federal regulations.

Previous guidelines for emotional support animals were more broad.