A horse is a horse, of course.
That's why business owners are getting nervous about a new federal regulation requiring a particular breed of horse to be allowed into shops and restaurants across the country.
The Justice Department regulations were tailored for so-called "service" horses -- miniature horses that, like service dogs, accompany the blind and others with disabilities to help them get around.
But the rules were a lawsuit waiting to happen, according to critics. And sure enough, a suit was filed earlier this month in Los Angeles, by a man who uses a wheelchair and keeps a miniature horse named Princess -- and who claims a local GameStop and Marshalls refused him and his horse service.
The case, as well as the regulation, has drawn concern from at least one lawmaker on Capitol Hill, as well as the National Restaurant Association.
"I like horses. My daughter likes horses. But even in the Wild West, they put them outside," said Angelo Amador, vice president of the restaurant association.
The organization has a few gripes. First, many business owners just don't know about the rule, and are only familiar with dogs being a traditional service animal. Amador said those that do know have concerns the animals aren't housebroken.
"You cannot train a horse ... housebreak them like you would do with a dog," he said.
The owner could claim the horse is housebroken, but if that turns out not to be the case then the business has a sanitation problem on its hands -- rather, its floor.
"After the deed is done, you have a number of other issues in the restaurant," Amador said. "It's kind of like damned if you do, and damned if you don't."
Rep. Jason Chaffetz, R-Utah, cast the rule as a case of Washington overreach -- hardly one to resist a pun, he accused the Justice Department of "making more hay" for trial attorneys.
"Do we really need to saddle businesses with more regulation? I say, 'Naaayyy.' Every scenario in life does not need a rule or regulation," he said in a statement to FoxNews.com.
The regulations on service animals were first put out in September 2010, as part of the Americans With Disabilities Act.
The rules, which went into effect later, actually narrowed down what used to be a broad definition for service animals. For most purposes, the Justice Department decided to recognize only dogs -- but the department added an exception for miniature horses after being "persuaded" regarding their benefits to the disabled.
The guidelines noted that the horses can be "viable alternatives" for people who are allergic to dogs or whose religious beliefs do not allow them to be around dogs.
"Another consideration mentioned in favor of the use of miniature horses is the longer life span," the guidelines said. They can provide "service" to the disabled for more than 25 years, as opposed to roughly seven working years for the typical dog. Plus the horses, despite their petite size, can be stronger.
That was the case for Jose Estrada, the plaintiff in the case filed this month in Los Angeles court.
His attorney, Morse Mehrban, told FoxNews.com that a dog "doesn't have the sufficient strength to pull him in his wheelchair."
So Estrada, a paraplegic, uses a 29-inch-high miniature horse named Princess. According to the complaint, the two retail stores being sued "refused to permit said animal" inside along with Estrada last month. The suit says Princess "is housebroken" and would not "compromise" the safety of those two stores.
"Apparently, they don't understand that a miniature horse can be a service animal," Mehrban said.
Estrada is suing for "no less than" $4,000 in damages.
The federal rules state that businesses should allow in the horses as long as they're trained, considering such factors as the size of the horse, whether it's under control, whether it's "housebroken," and whether its presence would compromise "legitimate safety requirements."
Amador says the horses cannot be housebroken.
The Guide Horse Foundation, though, says on its website that the horses "learn exactly the same behaviors as a guide dog," and that they "never bite or kick except when attacked."
The organization could not be reached for comment.
The use of miniature horses as service animals, though, has created a bit of a rift in the miniature horse community.
The American Miniature Horse Association does not condone the use of miniature horses for that purpose. Association President Harry Elder applauded those who have received "ADA certification" to train animals but questioned the use of miniature horses.
"Although the American Miniature Horse is bred to be intelligent, curious, gentle, sensible, willing to cooperate and easy to train, it remains in all respects physically and instinctively a true horse. The American Miniature Horse can be readily trained to be lead or driven but, in most cases, it would not make a suitable replacement for an animal such as a guide dog," he said in a statement.
According to the group, there are 200,000 miniature horses registered with the organization around the world, though it's unclear how many are used as service animals in the U.S.
Other retail groups are taking the Justice Department rule in stride and say they're trying to follow it. Mallory Duncan, senior vice president with the National Retail Federation, said the group is continuing to hold talks on "how best to comply."
"Retailers are sensitive to the many challenges confronting our customers and work to reasonably accommodate all shoppers when and where appropriate," Duncan said. "Retailers must remain cognizant of the unique challenges service animals present in the retail setting in order to best protect and serve the general public."