"We used to breed dogs for specific purposes, like they all had a job, they all work to do, so their bodies reflected the work they need to do," said veterinarian Ted Morris in an interview with North By Northwest's Sheryl MacKay.
"But now they're all being bred purely for their looks, so we're really breeding in some very extreme characteristics for them."
Morris says there are significant health impacts for the animals, as well as financial consequences for their owners. Here are some things Morris says pet owners should know before they choose dogs for their giant sizes.
Larger breed dogs don't live long
"It's not unusual for a very giant dog to only live to be maybe six or seven years," he said. "Great Danes are big heartbreakers because a lot of them, they hit the age of six and they just kind of keel over while you're out for a walk."
They suffer all sorts of health issues
"Heart disease is a major problem with these guys, and joint problems," said Morris. "Their bodies just aren't designed to get that big, so they end up with arthritis and a lot of torn ligaments and hip dysplasia."
They're expensive to keep
Morris says food and medication all cost more for a large dog.
"We base our medications on weight," he said. "So even something as simple as a dog who needs some antibiotics — you have a dog who's four times the average, their drugs are going to cost four times the average."
Morris says miniature dogs also suffer particular health issues like bad teeth, and knee and liver problems.
To hear the full interview with Ted Morris, click on the audio labelled: The pitfalls of extreme-sized pets