What you need to know to keep your dog safe in the heat this summer

Finally, the sun is starting to make a regular appearance in the UK again. The annual #DogsDieInHotCars campaign has officially launched (more on this shortly), which means summer is coming! And we have a new publication to share with you and some tips for risk assessing your dog’s safety in the warmer weather.

Our latest research paper reviewed all of our previous findings to identify the risk factors for severe and fatal heat-related illness (HRI). We also explored two important additional factors for UK dogs: location, and ambient temperature. If you want to read the full results they are available open access here:

Risk Factors for Severe and Fatal Heat-Related Illness in UK Dogs—A VetCompass Study

So which dogs are at greatest risk of heat-related illness?

Our previous research showed that overall, HRI is more likely to affect certain breeds (the Chow Chow, Bulldog, French Bulldog, Pug, Golden Retriever, Greyhound and Cavalier King Charles Spaniel to name a few), dogs with flat-faces (brachycephalic dogs), overweight dogs, older dogs, large breed dogs and purebred dogs in more affected. We also know that exercise is the most common cause of HRI in UK dogs, triggering almost 75% of cases, and some breeds (those listed above plus the Labrador Retriever, English Springer Spaniel, Staffordshire Bull Terrier and Border Collie) are more likely to develop HRI due following exercise.

But it is important to recognise that HRI is progressive disorder, meaning dogs start with mild disease but can progress to more severe, potentially fatal disease if their temperature continues to climb or remains too hot for too long. Over 90% of dogs presented for veterinary treatment with mild to moderate signs of HRI survived, whilst more than half of those presented with severe disease died. Our latest research paper specifically explored the factors that make severe and fatal HRI more likely once a dog is affected.

Which dogs are most likely to develop severe disease?

Severe HRI is characterised by vomiting and diarrhoea with blood present, repeated or continuous fitting (seizures), neurological damage (such as loss of consciousness and uncoordinated movement), bleeding disorders and kidney and liver damage. Less than half of the dogs with severe HRI will survive, despite veterinary treatment. If your dog develops HRI, the following factors make it more likely that they will develop severe disease:

AGE: Dogs aged 4 years or over (and particularly those aged 12 years or over) at more likely to develop severe HRI than dogs aged under 2 years of age. This is likely due to a number of reasons related to both lifestyle and lifestage. In people, young men are more likely to develop HRI caused by exercise because they are more physically active (either due to sports or physically demanding job roles). Older people are more at risk of environmental HRI (HRI triggered by heat waves or just hot weather) because they cannot cool down as effectively as mechanisms such as a sweating become less effective with age as heart function deteriorates. We suspect the same is true for our canine companions (whilst dogs do not sweat to cool, they still rely on mechanisms that need strong blood flow). Certainly older people and animals struggle to keep cool in the heat, and this is worsened by conditions such as heart disease, obesity, and breathing problems.

BODYWEIGHT: Dogs also have to obey the laws of physics so bigger, heavier dogs will get hotter quicker during exercise (more muscle to generate heat), and lose heat more slowly than small dogs. Dogs weighing under 10kg are less likely to develop severe HRI, and this is because they can cool more quickly, so don’t stay hot for as long as larger dogs. It could also be because small dogs are more likely to be carried, so if they get too hot we can pick them up, which helps to stop them getting hotter on walks.

EXPOSURE TO HEAT: This one is important. Dogs don’t die just in hot cars. Anything that causes a dog’s body temperature to rise and remain high can potentially lead to HRI, including hot weather, hot cars, hot buildings, being trapped in hot blankets, getting stressed at the groomers or at the vets, and most commonly getting hot whilst exercising. Dogs left in hot cars are more likely to develop severe disease compared to dogs that develop HRI following exercise. Why is this important? Because the key factors here IS YOU! If you leave your dog in a hot car, they are alone. Dogs don’t have thumbs, they can’t open the window to escape, you are leaving them to cook. UK cars can reach over 50°C, and can reach that temperature rapidly in direct sunshine. In comparison, dogs that develop HRI following exercise are usually with their owner, so you have an opportunity to spot the early signs of mild to moderate disease and take action before the disease can progress to the potentially deadly severe form.

That’s not to say that exercise induced HRI isn’t deadly, in fact more dogs died due to HRI following exercise than died following vehicular HRI, because the vast majority of dogs affected by HRI in the UK were triggered by exercise. So you can make a real difference here, and if the weather is heating up, stop and think carefully – if in doubt, don’t take them out!

This year (2022), the Dogs Die in Hot Cars campaign has been expanded to include this new message, Dogs Die on Hot Walks, all down to our Hot Dogs research.

Which dogs are most at risk of dying from HRI

Unsurprisingly, dogs that develop severe HRI are most likely to die. In fact they have 65 times the odds of death compared to dogs that only develop mild disease – and remember these are all dogs that presented to a vet for treatment. So knowing the early signs of HRI, and taking action to prevent the condition from worsening by cooling, stopping exercise, getting the dog into a cool area and seeking veterinary treatment can save your dog’s life.

Again, older dogs (this time dogs aged 8 years or older) are more likely to die if they develop HRI. This is likely due to a number of factors, including the fact that older dogs are more likely to have underlying health problems that impact their odds of survival.

Dogs with flat faces (brachycephalic dogs) are more likely to die if they develop HRI. This one is really important. Note that being flat faced DID NOT increase the risk of developing severe HRI, and whilst we can’t prove why, we have a theory we urge all flat-faced dog owners to consider. The first sign that indicates your dog is too hot is panting. In a healthy dog with a healthy respiratory tract, panting is normal and incredibly effective at cooling. If your dog has ANY kind of respiratory disease – specifically brachycephalic obstructive airway disease or BOAS – then panting is not as effective (so they don’t cool as quickly) AND panting requires more work, meaning the muscles driving panting can end up generating more heat than the panting can lose. In severe cases (again BOAS but also laryngeal paralysis), panting can cause further narrowing of the airway, leading to a lack of oxygen, which can lead to cardiac arrest and ultimately death.

A French Bulldog panting before BOAS surgery to open up their airways. Note the very narrow nostrils that restrict airflow.

Not all flat-faced dogs have BOAS though, so this isn’t quite enough to explain this finding. But, remember the signs of moderate HRI include excessive salivation and vomiting, and can include fitting and collapse. Flat-faced dogs are at increased risk of aspiration pneumonia following vomiting (basically inhaling the vomit into the lungs causing massive damage to the lung tissue), which will again lead to a lack of oxygen, cardiac arrest and ultimately death. So if you own a flat-faced dog, you need to take even mild signs of HRI really seriously, and seek veterinary advice immediately as your dog is three times more likely to die than most.

Does it matter where my dog lives?

Perhaps not as much as you might think, and UK region didn’t increase the risk of either severe or fatal HRI for dogs affected by HRI. But we did find that dogs living in London were more likely to develop HRI than dogs living in the North-West. Overall, around 1 in 2500 dogs developed HRI in the UK during 2016, in London this increased to 1 in 1250 dogs.

We also found that dogs living in London were more likely to develop HRI following confinement in a hot building. Nationally, only 3% of canine HRI cases were caused by hot building confinement, but in London that figure rose to 7.6%. We suspect that the urban heat island effect (lots of concrete, tall and terraced buildings, and not enough trees) contributes to this finding. We also found that dogs living in London were much less likely to develop HRI following confinement in a hot car, the reason for this isn’t clear but may be due to different transport preferences with significantly fewer London households owning a car.

So, how hot is too hot?

We get asked this question A LOT, and I’m afraid we have come to the challenging conclusion that it’s just not that simple. We can’t give you a number. This is where risk assessment comes in. Lets take the Hot Dogs team as an example. Anne competes in both canicross and bikejor with her dogs, and is incredibly active and physically fit. If you send her out for a 5km run in 20°C, she’ll be fine (FYI she wouldn’t be taking her dogs at that temperature!). Emily is a self confessed sofa pumpkin (we explained this term previously), she hasn’t competed in any sports for many years now and is no where near as active as Anne and not very physically fit. She also has asthma, so there’s an underlying respiratory disease to consider as well as a greater bodyweight (ahem!). Firstly, Emily couldn’t run 5km even with zombies chasing her. If she tried, there is a very real risk she would develop HRI not matter the ambient temperature. Our dogs are just as variable, they will react differently to ambient temperatures depending on a whole host of factors including bodyweight, breed, skull shape, general health, physical fitness, acclimatisation, hydration status and even diet.

Even more concerning, in our latest paper we reported the highest daily “feels like” temperature (this is “wet bulb globe temperature”, which takes into account air temperature, humidity, wind speed and solar radiation) recorded at the nearest weather station to each HRI event we studied. The average (median) temperature was just 16.9°C. The lowest temperature was 3.3°C (for an exercise induced HRI case), whilst the highest temperature was 23.1°C. These are not high temperatures. In Israel a similar study found that 85% of HRI cases occurred on days with a feels like temperature of 24.1°C, so dogs in the UK develop HRI at much lower temperature than dogs living in hotter climates.

When judging temperature conditions for your dog, you also need to consider how temperature is being measured. We used local weather station data, meaning the temperatures were recorded in the shade. Your back garden, in full sun, with fences or hedges reducing wind and airflow, could be significantly hotter than the “feels like” temperature being reported on your weather app or weather forecast. If you have a lot of tarmac or artificial grass in your outdoor space, this will cause further heating and can even cause contact burns if your pet walks or lies on a hot surface.

So how do you keep your dog safe this summer?

Firstly, if in doubt, don’t take them out. No dog will die from a missed walk, but exertional HRI can be fatal. If you are travelling with your dog, then ensure you have carefully planned your journey and can take action should you break down or get stuck in traffic. Never leave your dog alone in a vehicle that could overheat.

Consider the conditions and the recent weather conditions:

  • Sudden hot spells are most dangerous as you dog can take about 6 weeks to acclimatise to heat.
  • Consider the time of day, early mornings are typically cooler, as usually the temperature drops overnight. Evenings can be hot and in particular the ground (where your dog will be walking/lying) may be very hot.
  • If you can exercise your dog in shaded areas like woodland, this can help limit their heat exposure.
  • If you are planning intense exercise with your dog, frankly anything over 10°C should be prompting a risk assessment.

Is your dog at greater risk?

  • Are they an at risk breed?
  • Are they flat-faced?
  • Do they have a respiratory condition such as laryngeal paralysis or BOAS?
  • Have then recently been unwell, this includes dehydration from not eating, vomiting or diarrhoea?
  • Are they physically fit?
  • Are they overweight or obese?
  • Are they a large breed dog?
  • Do they have a thick fluffy coat (this is particularly important for exercise, not so much for lazing around)?
  • Are they older?
  • If you answer yes to any of these questions then you need to take extra care when considering activity in even warm weather.

Make sure you can spot the early signs of HRI:

Being able to recognise the signs of mild HRI may save a life:

  • SPOT THEM – spotting the early signs will give you time to take action.
  • STOP THEM – from getting any hotter, e.g. stop the exercise, get them out of the hot car/building/garden.
  • SAVE THEM – seek veterinary treatment and cool them (using water)
Mild heat-related illness signs. Seeking veterinary treatment at this point will save lives.

Consider how you would respond if you dog developed HRI:

Things to consider include:

  • Access to water for cooling – cold water is ideal, so could be a stream, a lake, even a water trough or water from a bottle (although for big dogs a lot of water may be needed).
  • Transport to a vet – can you lift and carry your dog? If not, how far do you plan to be from a vehicle or help if your dog were to collapse?
  • Access to veterinary care – the UK (and international) veterinary profession is suffering from a serious workforce shortage, meaning some practices are struggling to provide a full service, and many practices are unable to take on new clients. If you are on holiday or away from home for the day, where is the nearest veterinary practice that could treat your dog in an emergency?

Unlike many conditions, you can protect your dog from heat-related illness, so make sure you take the risk seriously this summer and know the early signs so you can take action if the need arises. Remember, if in doubt, don’t take them out.

Hendricks napping on a hot day, staying safe by keeping cool out of the sun.

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