Thirty-eight French bulldogs have been found dead on a plane that was carrying at least 500 puppies to Canada.
The dogs that survived the flight from Ukraine to Toronto on June 13 were suffering from symptoms including dehydration, weakness and vomiting, officials said on Saturday.
Canadian authorities have launched an investigation to determine what happened to the puppies.
The Canadian Food Inspection Agency said in a statement: "Upon inspection, it was found that 38 were dead on arrival.
"Ukrainian International Airlines is a member of the International Air Transport Association, which has voluntary guidelines airlines should follow to ensure animals are transported safely.
"CFIA officials are currently investigating the circumstances surrounding this incident and will determine next steps once the investigation is complete."
Dog handler Abby Lorenzen, who was in the airport cargo to pick up another animal, told CBC News the scene was like a "horror show".
"It was just a nightmare," she said. "Canada and the federal government need to change the laws on the importation of these puppies."
Ukrainian International Airlines said in a statement: "Everyone at UIA offers its condolences for the tragic loss of animal life on our flight.
"UIA is working with local authorities to determine what happened and to make any changes necessary to prevent such a situation from occurring again."
Professor Scott Weese of the University of Guelph, who works with Public Health Agency of Canada, said online ads such as Craigslist show that there is a lucrative market for the sale of puppies that are believed to be bred in Canada.
He said: "We really have no idea [what] the scope of the issue is. We have no idea how many dogs come in, where they go, where they come from.
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"It is a big industry. There's no doubt about it. And it's been looked at more in the US and there's potentially some organised crime component of it, too, in some areas.
"You mentioned 500 French bull dogs. If those are going for sale at $3,000 [£2,400] to $4,000 [£3,200] a dog, that's a massive amount of money."
