A new study involving more than 19 million cats from across Canada and the United States suggests most of the animals continue to put on weight after they reach adulthood, and their heaviest weight is higher now than it was two decades ago.

Researchers at the Ontario Veterinary College at the University of Guelph analyzed 54 million weight measurements taken at vet offices between 1981 and mid-2016 to get a sense of the typical weight gain and loss pattern over the course of a cat's life.

They say the study, published in the Journal of the American Veterinary Medical Association this week, is the first of its kind to use such a large pool of data.

Overall, the data showed cats' mean weight reached its peak between six and 10 years of age for the most common purebred breeds — Siamese, Persian, Himalayan and Maine coon — and at eight for domestic cats of mixed ancestry.

Male cats generally hit higher weight peaks than female cats, and cats that were spayed or neutered tended to be heavier than those that weren't.

The findings showed a difference of about one kilogram between age one and the peak. As well, the mean weight of neutered, eight-year-old domestic cats rose about 1/4 of a kilogram between 1995 and 2005 and then remained steady for the next decade.

"It might not seem like much, but half a pound is still a significant amount for a cat," said lead author Adam Campigotto.

The study is meant as a starting point for further research and did not look at what caused the changes in weight, nor did it establish what a healthy weight is, said Campigotto.

He said some possible, untested explanations for the shift include:

More people may have begun to keep their cats indoors during that time period.

Improvements were made to the palatability of cat food.

Changes in pet owners' feeding behaviours.

"Treats can have a big impact on weight for their animals and often people associate giving treats as a kind of love," he said.

The researchers said slightly more than half the cats involved in the study had only one weight measurement in their veterinary file, which they said suggests the animals' owners may not have scheduled regular vet visits or may have switched clinics.

Changes in the palatability of cat food could be contributing to an obesity trend in North American cats, veterinary researchers say. (Rachel Denny Clow/Corpus Christi Caller/Associated Press)

However, the sheer number of records collected meant researchers were able to fill those gaps by combining all values for each year of age, the team said.

Another of the study's authors, Theresa Bernardo, who is also a professor at the Ontario Veterinary College, said pet owners may want to begin weighing their cats at home if it isn't being done at the vet. Weight changes may be linked to other health issues such as diabetes, some cancers and arthritis, though those correlations were not drawn in this study, she said.

"Obesity is a growing concern in the human population as well as in many non-human animal species in contact with people, including domestic cats," the study's authors wrote.

One of the next steps will be to look at how to manage cats' weight, Bernardo said.

As more cats spend time indoors, they also tend to become more sedentary, says Dr. Scott Bainbridge. (CBC)

"We have another project where we're looking at using technology like automated feeders," she said.

"In many cases, there are multi-cat households and sometimes one cat is eating a good share of the other cat's dinner, so there are feeders now that will actually feed each cat separately, which helps you get a hold of that kind of situation."

'Food is love'

At the Dundas West Animal Hospital in Toronto, Dr. Scott Bainbridge turned to an automated feeder after their in-house cat, Bonnie, was lovingly overfed by multiple staff members.

Bainbridge, a veterinarian who wasn't involved in the study, said he's observed similar changes as the authors in his feline clients.

"Food is love sometimes," Bainbridge said. "A way to show affection to your cat is to continue to feed them and I think people have gotten away from actually measuring how much food they're supposed to have."

As more cats spend time indoors, they also tend to become more sedentary and put on weight, he said.

The study's findings can help vets discuss health issues related to weight with cat owners, the researchers said. More work is needed to explore the links between cats' body weight and various conditions, they said.