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Flat-faced dogs such as bulldogs, French bulldogs and pugs most at risk of heat stroke, study shows

Breeds with flat faces (brachycephalic) – such as bulldogs, French bulldogs and pugs – are particularly at risk of developing heat stroke, the largest study of its kind suggests.

Bulldogs are one of the breeds most at risk of heatstroke, the study found

Researchers in dog welfare at Nottingham Trent University and the Royal Veterinary College analysed the anonymised clinical records of more than 900,000 dogs across the UK.

They found that more than 1,200 dogs had received veterinary care for heat stroke during the study, with almost 400 affected in a single year. This is just the tip of the iceberg as many dogs affected with heat stroke may not even be taken to a veterinary surgery.

Many of the breeds that were at increased risk were flat-faced meaning that they had a ‘brachycephalic’ skull with a shortened head, flat face and short nose.

The Labrador retriever – traditionally the most popular UK breed – was used as the ‘base’ comparison breed to identify breeds at most risk.

The Bulldog, an extreme flat-faced breed, was 14 times more likely to develop heatstroke than Labrador retrievers, whilst flat-faced dogs in general were twice as likely.

The study identified that the following breeds were most at risk: Chow Chow (x17); Bulldog (x14); French Bulldog (x6); Dogue de Bordeaux (x5); Greyhound (x4); Cavalier King Charles Spaniel (x3); Pug (x3); Golden Retriever (x3), Springer Spaniel (x3).

“It’s likely that brachycephalic dogs overheat due to their intrinsically ineffective cooling mechanisms”, said Emily Hall, lead researcher and a veterinary surgeon at Nottingham Trent University’s School of Animal, Rural and Environmental Sciences.

She said: “Dogs pant to cool down – without a nose, panting is simply less effective. In fact, brachycephalic dogs may even generate more heat simply gasping to breathe than they lose by panting.”

The researchers say that the increasing popularity of these flat-faced breeds is concerning, particularly as climate change increases the severity and frequency of heat waves.

These twin trends of increasing numbers of flat-faced dogs and rising UK temperatures will result in even more dogs suffering from this potentially fatal heat stroke condition over time, they say, and vets should weigh up potential risk of heat stroke when advising owners on breed selection.

The Chow Chow and the Golden Retriever, which were also at high risk, have thick “double coats” which limit effective cooling in hot weather, because the coat traps warm air against the body to prevent effective cooling from the skin.

As well as breed, the study identified some other important predictors for heat stroke in dogs, including being above average weight and being over two years old. Dogs that were big for their breed – including both obese dogs and large or muscular dogs –  had almost one and a half times the risk compared to those that were smaller than the breed average.

Dogs weighing 50kg or above had almost three and a half times the odds of heat stroke compared to dogs weighing under 10kg.

Emily added: “We hope that our findings will help both veterinary professionals and dog owners to identify those dogs at increased risk, so that they can make potentially life-saving decisions such as avoiding exercising their dogs during hot weather.”
The study, published in the journal Scientific Reports, showed that heat stroke can have very severe effects in dogs, with one in seven dogs with heat stroke dying as a result of their illness.

Dr Anne Carter, Senior Lecturer in Animal Science at Nottingham Trent University, said: “Our research is particularly pertinent as the UK’s annual “Dogs die in hot cars” campaign has just been launched, a sad reminder that people still put their pets’ lives at risk every year by leaving them to suffer in hot cars. Our study also suggests that preventing obesity will reduce your dog’s risk of heatstroke.”

Dr Dan O’Neill, co-author and senior lecturer in companion animal epidemiology at The Royal Veterinary College, said: “As the UK moves progressively towards higher average temperatures due to global warming effects, we all need to wake up to the changing health hazards that our dogs will increasingly face.

“Greater understanding of which breeds, ages and types of dogs are at extra risk of heat-related illness can assist owners to select breeds that are more resistant to heat effects and to plan how best to protect predisposed dog types from their increased risk by, for example, altering times and levels of outdoor activity. Knowledge is power when it comes to protecting our beloved dogs. A core message from this study would be to “stop and think before buying a flat-faced dog.”

This study is part of the ongoing VetCompass research programme at the Royal Veterinary College that aims to improve companion animal welfare and was supported by a Dogs Trust Canine Welfare Grant. Paula Boyden, Veterinary Director at Dogs Trust, said:“We are pleased to have been able to support this work. Dogs are unable to regulate their body temperature as well as humans do, so as the weather warms up, we need to be alert to the signs of heat stroke. These findings show that owners of flat-faced breeds and dogs who are overweight, need to keep an especially close eye on their beloved pet during the warm weather as they could be at greater risk.

“The good news is there are lots of things we can do to make sure our dogs stay happy and healthy in hot weather, whether outside or playing indoors as many of us are at the moment.

“Make sure they have plenty of shade and water, and if you need to head out in the car with your dog, please be very careful. As little as twenty minutes can prove fatal if a dog is left alone in a car on a warm day.”

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  • Notes for editors

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    This full paper is freely available open access at:

    Purebred dogs in general had almost twice the risk of heat stroke compared to the typically more vigorous crossbreeds. However the Labrador Retriever, traditionally the UK’s most popular breed, was at no greater risk when compared to crossbreeds, so all other breeds were compared to the Labrador.

Flat-faced dogs such as bulldogs, French bulldogs and pugs most at risk of heat stroke, study shows

Published on 18 June 2020
  • Subject area: Animal, equine and wildlife
  • Category: Press office; Research; School of Animal, Rural and Environmental Sciences

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