Our latest study looked at temperatures falling outside the range of 8-25°C . Broadly speaking, 25°C is the upper comfortable threshold for dogs to control their body temperature, slightly above the upper limit for some brachycephalic dogs to cool themselves unaided. This range is also the temperature threshold for the storage of many veterinary and human drugs, outside of which they can lose their efficacy with potentially dangerous consequences. An additional threshold over 35°C was included, at which point all dogs struggle to thermoregulate, particularly when enclosed in a car with no air movement.
The internal temperatures of four cars were monitored over a two-year period. This allowed us to monitor the temperatures 24 hours a day (no dogs were kept in the cars for the purposes of the study!). By the end of the study period, we had between 7300 and 17800 individual temperature readings for each month of the year. This allowed us to look at the impact of time of day and seasonality on internal car temperature.
UK car temperatures
Internal car temperature ranged from -7.4°C to 54.5°C with temperatures dropping below 8°C in every month except June and July. Temperatures exceeded 25°C in every month of the year and above 35°C from April to September. And whilst early mornings were generally cooler, temperatures over 35°C were recorded between 8am and 9pm.
The highest temperature recorded was 54.5°C
It is also worth bearing in mind that the risk may extend beyond stationary vehicles. Sitting in traffic on a hot day, or an air conditioning system failure could also be lethal for dogs trapped in the car.
This study highlights the year round risk to dogs in cars and the need for constant vigilance. This is particularly the case for those breeds and types of dogs considered more at risk of heatstroke, such as brachycephalic, overweight and older dogs.
The study highlights that the risk to dogs in cars is year round, not just restricted to the traditionally warmer summer months. Heat-related illness can be fatal so whenever dogs are in cars, owners should be cautious. Whilst traditionally the advice is to avoid exercise during the midday heat, peak car temperatures occurred between 14:00 and 17:00 hours from March to October. So late afternoon, from spring to autumn is the most at dangerous time for dogs in cars.
After what feels like an eternity (and is in fact just under 2 years!) we can FINALLY share the first set of results from our Hot Dogs VetCompass project – exploring the risk factors, incidence and fatality of heat-related illness in UK dogs.
The paper is fully open access, so you can either view it on-line here:
You may have been wondering where we’ve been and what we’ve been up to, as it seems an age since we last shared any updates on our canine heatstroke research project…
Well, we finally have some exciting news!
Hot Dogs at BSAVA Congress 2020
Last month Emily presented two abstracts (preliminary findings) at the British Small Animal Veterinary Association’s annual Congress. Whilst the live event was an early casualty to the COVID19 lockdown, the abstract session was moved on-line in May, reaching a virtual audience of over 160 veterinary professionals from around the world.
The first abstract summarised our first study using the VetCompass TM database, reviewing the anonymised veterinary records of over 900,000 UK dogs to explore canine risk factors for heat-related illness. This abstract can be downloaded in text form below, or you can watch a recording of the presentation.
The second abstract explored the “triggers” for heat-related illness in UK dogs, reporting the most common reasons dogs develop heatstroke, and which reasons had the highest risk of causing death. This abstract can be downloaded in text form below, we hope to be able to share the video soon.
Findings from our VetCompass study will be published 18th June at 4pm!
Finally, our first Hot Dogs VetCompass study will be published TOMORROW AFTERNOON, where we report the incidence, fatality rate and canine risk factors for heat-related illness in UK dogs (the full paper of the first abstract). Thanks to a Dogs Trust Canine Welfare Grant this paper is Open Access, meaning you will be able to read the full version for free just as soon as it is published!
Watch this space for updates, we’re hoping it’s going to be a busy summer sharing our research, to help you make safer choices for your dog.
You only need to step inside a pet shop to see the vast array of collars, harnesses and leads available to dog owners. Owners can choose a particular look, colour scheme and material type. But amongst all of this, there is a more serious question of the role of the collar and the impact it may have on the dog. Historically, collars were used as a means of identifying a dog as being owned. Today, in the UK, as in many countries, it is a legal requirement for a dog to wear a collar and tag to provide key information about the dog, in order to identify the owner and to return it should it become lost. However, collars are now commonly used as a means of restraint and control for dogs to make sure they don’t wander off when out for a walk.
The problem is that the neck is a pretty sensitive area of the body, and many dogs pull on the lead. Ultimately, the neck connects the head to the rest of the body, carrying some pretty vital anatomical features such as the spinal cord, major blood vessels, the windpipe and the food pipe. Serious damage to the spinal cord in the neck can result in paralysis, or even death. Similarly, damage to the windpipe can impact a dog’s ability to breath or even result in choking, another potentially fatal injury. Linking to our normal research area, heat-related illness, compression of the windpipe can impact a dog’s ability to breathe effectively, impairing their ability to cool. When it’s hot outside, allowing a dog to pull on a collar and lead could potentially result in them over heating more quickly.
In fact, when questioned, almost 50% of owners suggested that their dogs pulled on the lead. This might range from a consistent light pull, to an owner being ’towed’ up the street by an overzealous dog. And of course, there is the sudden jerk on the lead from a normally calm dog, as a cat goes running across the road. On the other end of the lead is the owner, perhaps getting a little impatient at the 17th lamppost being sniffed, and offering a quick tug on the lead, or the frustrated individual jerking the lead to remind their dog to listen and behave. In all these instances, the resulting impact is a pressure applied to the dogs’ neck.
Two aspects are worth exploring; the impact of the type of collar – are some better than others? And the impact of the force applied – is a light pull on the lead less likely to cause harm?
The forces tested aimed to replicate a light pull on the lead (40N), a strong pull on the lead (70N) and a lead jerk (~141N).
The collars reacted differently in both the way the pressure was distributed and the amount of pressure applied to the model neck, the pressure increased as the force applied to the collar increased. Arguably the most interesting and valuable finding was that the pressure exerted on the neck model ranged from the lowest, 83kPa at 40N to the highest, 832kPa at 70N across the range of collars. To put this into context, in humans, pressure over 33.3 kPa has been shown to increase intraocular pressure (pressure within the eyeball which can lead to pain and ultimately blindness) and compress blood vessels, limiting blood supply to tissues. Tourniquets used in emergency situations to stop serious blood loss following trauma are used at a pressure of 33.3kPa on the arm and 40.0kPa on the thigh. In horses, pressures above 30kPa under the saddle are associated with back pain.
In short, no single collar tested provided a pressure anywhere near low enough to remove the potential risk of injury when pulling on the lead. Where dogs pull on the lead or the lead is jerked, there is a risk of injury to the neck for all collar types and styles tested, even where collars are padded or wide fitting. Collars are a great way to display tags and add a little personal flare to your dog. But for restraint and control, a non-restrictive harness is a much better option, and in hot weather a harness is definitely the safest option.
The average car is a metal box with glass windows. Metal is an excellent conductor of heat, meaning heat can pass through metal easily, think of your kitchen saucepans. Glass is a poor heat conductor but allows sunlight to pass through. This means that light energy from the sunlight enters the car through the windows but then gets trapped as heat by the glass. Some of this heat will be lost through radiation and conduction into the surrounding air, but if sunlight continues to fall on the car, it will continue to heat and in summer, this happens far quicker than heat can be lost to the environment; the reason greenhouses are so effective. The net result is your classic summer hot car.
The typical British summer is an unpredictable affair. Whilst temperatures regularly reach 20oC or more, often we have consistent cloud cover, intermittent rain or high winds to keep things feeling fresh, and stop cars turning into ovens. Last summer, we experienced one of the first prolonged heatwaves of this century, with temperatures regularly hitting 30oC and endless blue, cloudless skies. We have become complacent. Our dogs are typically part of our family, so we like to take them with us, whether we are taking them for a walk, for a day out, or travelling somewhere. The problem is, on a typical sunny day of 21oC, your average family car will reach temperatures of 31oC in 10 min. As the outside temperature climes to 31°C, the internal temperature of the car can reach 54°C. 80% of that temperature rise happens in the first 30 minutes.
We’ve all seen the adverts, surely no one would be so stupid…?
Since 2016, summer has been heralded by the “dogs die in hot cars” campaigns supported by a number of charities to increase awareness of the risk of leaving dogs in cars in the summer, and yet last year (2018) the RSPCA received 8290 calls, an increase from around 7800 calls concerning heat exposure in animals 2017. In a single weekend, over the 2018 May Bank holiday weekend, 217 calls were made by people concerned about dogs left in hot cars. One London police force was even offering a ‘free ventilation service’ if dogs were left in cars during the hot weather (by breaking the window).
So why do people leave dogs in hot cars? A two-minute trip into the shop for a couple of forgotten items can easily become ten minutes. When questioned, owners gave a range of excuses, from “My dog is white, he’ll be fine” to “We feel bad leaving him at home on his own all day.” “We didn’t think we’d be long.” “It’s OK, I’m a vet”. No doubt, the vast majority of people do not want to harm their dog, but simply do not think. When leaving the car, the air con or open windows from travelling can make the car feel relatively cool. However, left in the sun for any length of time, even with the windows cracked slightly, it will get hot. Shade can help to keep the car cooler, but as the sun moves round, the shade can quickly disappear.
A human in a similar situation would begin to sweat to try and lose heat. Dogs don’t have the ability to sweat, they will pant, but as the temperature continues to rise, panting becomes less effective, and once the car temperature exceeds body temperature (around 38oC) there is nothing the dog can do to cool down. Unless the dog is actively cooled (see below) their body temperature will rise with the car temperature, and once they exceed 41oC, they are likely to develop heatstroke.
Heatstroke – the problem
Heatstroke isn’t the same thing as sun stroke, or heat cramps, or heat exhaustion. These conditions can often be treated with cooling, plenty of fluids and rest. True heatstroke causes multi-organ failure. Picture an egg in a frying pan, you crack the egg, the yolk is yellow but the egg white is clear and jelly like. Once the egg starts to heat, the chemical structures of the proteins start to change, the egg white becomes firm and changes colour. Now imagine this happening to the proteins within the body. As body temperature exceeds 41oC the stomach and intestines stop functioning, so the dog may vomit or pass bloody diarrhoea. The kidneys stop working, so despite fluid therapy the dog is unable to flush out the toxins from all the cellular damage taking place around the body. If the dog’s brain overheats, they may start fitting, or fall into a coma. The mortality rate for dogs with heatstroke is up to 63%.
Don’t risk it.
Don’t keep your dog in the car and never leave them unattended. Even in the shade, car temperatures can increase quickly, and shade may disappear. Leaving windows partially open has little effect on car temperature. If you are stuck in traffic or travelling, have the air conditioning on to keep the car cool and make sure windows are shaded from direct sunlight. Don’t assume your dog in the car boot area is fine because you are, check them regularly, your air conditioning may not reach the boot. Ideally, leave your dog at home in hot weather. Car shields and shades may help to keep the car cool by reflecting the sun’s rays, but some may also act as an insulator, particularly if the car is already hot inside. If you have no alternative other than to keep your dog in the car, open all windows, open the boot, try and maintain airflow, park in shade, and don’t leave your dog. Stay with them so you can be absolutely sure they are OK.
If you see a dog in a hot car, the advice is to phone the police. Heatstroke can kill quickly. A dog that is suffering from heatstroke needs to be actively cooled and taken to the vets. Active cooling is key. Even before setting off to the vets, use water to splash the dog’s legs, belly and throat area, get them out of the sun and into the shade, and if possible move them somewhere with good air flow – this might be in a car with the air conditioning already blowing. To give you an idea, the army have been known to use the downdraft from helicopter rotor blades to create airflow over soldiers with heatstroke. Next, getting to the vets as quickly as possible is the current best advice. Avoid using ice or very cold water, as this can do more harm. When your skin is cold, the blood vessels constrict, which can make it harder to cool the dog, and increase the risk of them going into circulatory collapse (shock).
There is no guarantee any dog will survive heatstroke, so the best way to keep your dog safe is to prevent it.
If you’ve read any of our posts so far you will know we are all about monitoring body temperature, specifically as a means of understanding heatstroke risk in exercising dogs. As our fabulous friend Dr Jackie Boyd likes to remind dog owners:
Whilst Dr Boyd is referring to measuring food in relation to canine nutrition and weight management, the same applies to body temperature. You can only be sure your dog is not over heating if you measure their body temperature. You can only be sure your temperature management strategy is working if you continue to monitor their temperature. We’ve previously shared some advice on methods of monitoring body temperature in dogs and other animals, and we have an update coming on this topic very soon! Crucially though, if you’re going to measure your animal’s temperature, you need to know what the numbers mean, and how to react appropriately.
The “normal” range
For almost every measurable aspect of an animal, from age, height and weight, to temperature, heart rate or urine production, there are “normal” reference ranges. In theory, these are statistically calculated limits of the normal population; in other words, 95% of healthy animals will fall within this range – there are always extremes that don’t fit the normal limits.
Google “normal temperature for a human” and you will see the top result, Wikipedia, reports “The normal human body temperature is often stated as 36.5–37.5°C”. It goes on to mention that “In adults a review of the literature has found a wider range of 33.2–38.2°C (91.8–100.8°F) for normal temperatures, depending on the gender and location measured.” A study recently found that the long established “normal” body temperature for humans is too high, highlighting the continued use of out of date normal ranges by medical professionals all over the world. This situation is mirrored in animal species. Textbooks state the normal range for various biological parameters in almost every species, but rarely state where this reference range has come from, how old it is, which animals were used to establish it and how their temperature was measured.
Our primary interest is canine health and welfare, so this all started when we tried to find a reliable source stating the normal resting temperature for a healthy dog. We struggled. Every textbook listed a slightly different range, 37.9-39.9°C on one website, then 38.2-39.2°C in a veterinary nursing textbook. The most recent reference we found was in a paper measuring rectal temperature in 62 dogs presenting to a veterinary hospital for routine health checks, who reported a normal range of 37.2 to 39.2°C. However, this did not report how this range was calculated, so without details of the statistical methods used to determine this range, it can not be considered truly valid.
Where does this leave us? Well, at the moment, we don’t actually have a robust, recent, reliable normal reference range for canine body temperature, when measured with a rectal thermometer. Three different sources state that 39.2°C should be considered the upper limit of normal, so we are fairly happy to accept that as our upper limit. What we do have, is a scientifically calculated normal reference range for canine ear temperature – because we calculated it! We measured ear temperature 416 times, from 157 healthy dogs attending various canine sports events over a two year period. Importantly, these dogs were not at the vets, so whilst they may have been excited, they were not stressed or scared. We calculated the normal range to be 36.6-38.8°C.
Returning to rectal temperature, we know from our research, and from studies done by various other research teams around the world (Zanghi, 2016; Gomart et al., 2014), that ear temperature tends to measure around 0.4-0.6°C lower than rectal temperature. So, the rectal range of 37.2 to 39.2°C then quite nicely reflects our ear temperature reference range, just 0.4-0.6°C higher. This is the range we would consider to be most appropriate for interpreting canine body temperature, when measured with a rectal thermometer.
Equine body temperature
Because we are both slightly mad, some might say obsessive, we couldn’t stop at establishing a normal reference range in just dogs. Oh no, we had to look at horses too. Whereas a dog may try to escape, sit down, or worst case scenario bite should they resent having their rectal temperature measured, a horse can, and if suitably aggrieved will kick you. This can be catastrophic. So if you’re going to risk your life measuring your horse’s temperature, and there are plenty of reasons you should be doing this, we felt it our duty as scientists to ensure you have a means of accurately interpreting the result.
We started by trying to find the evidence behind the “normal temperature range” for horses. We failed miserably. Once again, whilst plenty of textbooks, websites and other studies investigating equine temperature all state what the normal temperature range for a horse is, none of them reported where this range came from. Similar to the situation in dogs, if you don’t know where a reference range came from – how many horses were included, what part of the world, what breeds of horse, who took their temperature, how was their temperature taken – how can you be certain it is relevant to your horse? The simple answer is, you can’t.
So we decided to establish our own reference range. The horses at our University Equestrian Centre are cherished; the team caring for them will (and have!) battle blizzards, tropical storms and heat waves to ensure these horses are fed, watered, comfortable and loved. Part of their routine husbandry includes temperature monitoring, and yes, being University horses they do have to work for their living, so they are often used in non-invasive research work like our study comparing rectal temperature to eye temperature (measured with a non-contact infra-red thermometer, and coming soon!). Working with Dr Carol Hall and Dr Anne Stevenson, we collated rectal temperatures taken from 41 of the horses on the yard, measured at rest during a number of projects and routine monitoring. This gave us over 600 resting, healthy horse temperatures, all measured with a digital rectal thermometer by a familiar person, in the comfort of their stable. Knowing the horses were relaxed and not stressed is important, as stress can influence temperature in horses and other species.
We used a statistical method to then determine our horse’s “normal” temperature range, basically the middle 95% of the temperature readings. On our yard, this was 36.0-38.0°C. The upper limit is particularly important, as it is around 0.5°C lower than most of the previously published normal temperature ranges for horses. When an animal’s temperature exceeds this upper limit of normal, they are considered to be hyperthermic, too hot. The temperature reading alone can not explain why the animal is too hot, but it is an important indicator that something isn’t quite right (or, the horse has been exercising or in a hot environment). The term pyrexia, or fever, describes an animal that is too hot due to illness, this could be an infection, inflammatory or painful process. A low grade fever is where an animal’s body temperature is just slightly increased above the normal range and can be an early indicator of disease. It is therefore important that the normal reference range is accurate, otherwise these early indicators of illness can go unnoticed.
It is worth noting again, that the method of temperature measurement used is really important to consider when assessing your animal’s health. True core body temperature can only be measured using invasive, or ingestible devices. Rectal temperature remains the most accurate estimate of core temperature in most animal species (thankfully in humans non-contact thermometers appear to be as reliable!), but even the depth of rectal thermometer probe placement can have an impact on the resulting reading. A difference of 1cm can impact the temperature reading in chinchillas, whilst inserting a probe to 15cm or deeper in horses is likely to result in a higher temperature reading being obtained. Whilst we have no published evidence to support our theory, we suspect inserting a rectal probe to 15cm or deeper may also increase your risk of being kicked, so our normal temperature range is based on a 5cm thermometer depth.
If you monitor body temperature in two different ways you will get two different results. We know ear temperature is typically 0.4-0.6°C lower than rectal temperature. So it is important that you use the same method of temperature measurement each time if you are going to monitor your animal for changes in body temperature. That said, if you are ever worried about your animal’s temperature, use a rectal thermometer as this is still the most reliable estimate of core body temperature. Also, see your vet. Both high and very low body temperatures can be fatal in all species, so if your animal is unwell DO NOT delay seeking veterinary treatment.
Our equine paper is available to read and download (free!) on the publisher’s site until 8th March 2019:
After this time, if you do not have access to the Journal of Equine Veterinary Science, then you are of course welcome to read the full article in the unfinished form below (this is the accepted manuscript, just not formatted into the journal’s style).
The Hot Dog’s team (Emily and Anne) are now working with Dan O’Neill from the Royal Veterinary College on a UK wide canine heatstroke study. The study will use data from the Vet Compass™ database to review the clinical records of over 900,000 dogs registered with UK primary-care veterinary practices for heatstroke events. As well as canine risk factors (e.g. breed, age, sex and bodyweight), additional information will be collected to establish the incidence, fatality rate, seasonality and underlying causes for canine heatstroke. Understanding the risk factors of heatstroke specific to the UK dog population will provide evidence to better support educational campaigns aiming to reduce or prevent this potentially fatal condition.
Thanks to some fabulous people we now have our activity survey available to complete in several different languages! If you know anyone with canine friends/family or businesses who speak the following languages please share 🙂
It all comes down to the skull. Firstly, a bit of background on how selectively breeding dogs for skull shape impacts the skeleton as a whole.
Dogs with a shortened nose (brachycephalic breeds) often also have a shorter, squarer pelvis. This has a cascade effect. It impacts how they walk, which in turn impacts the forces on their leg bones, which impacts the shape of the long bones. Tall, slender dog breeds tend to walk with their legs underneath their body, like a model on a cat walk stepping one foot in front of the other. This is the most efficient method of moving if you are a dog. As soon as the dog becomes broader, the chest becomes more barrel shaped, the dog walks with the feet either directly underneath the shoulder joint, or, in very barrel chested dogs they may even walk with the feet wider than their body, like a cowboy. This is not an efficient way of moving, but may be necessary for fighting. Traditionally, selective breeding aimed to develop a dog with a purpose. Sight hounds were bred for speed to catch prey, bull breeds were developed for their jaw strength for fighting.
This altered skeleton structure also causes the legs to move differently. In a Greyhound or Whippet, the legs simply swing back and forth, like a pendulum. The bones grow in an elliptical shape as this provides the best strength to withstand the force of trotting, running, jumping and landing. This again is streamlined and efficient. In a barrel chested breed, the legs don’t just swing back and forth, they twist and rotate to provide the same stride length. This twisting and rotating causes the bone to grow in a perfect circle, which is less aerodynamic and reflects the less streamlined motion. This means a barrel chested dog, which includes almost all brachycephalic breeds, has to work harder to move the same distance as a non barrel chested breed. This increased work, requires increased effort, which generates more body heat from muscle activity. They also tire faster, meaning exhaustion occurs more quickly.
What do bones have to do with heatstroke?
Dogs only sweat on their paw pads, so they rely on their breathing for temperature regulation. A dog’s long muzzle (nose) is a key method of cooling. Inside these long muzzles, are the nasal turbinates (see below), as series of scroll like bones that are coated in tissue similar to the surface of the lips and gums. These nasal turbinates hugely increase the surface area within the muzzle. This means a huge area of wet tissue is available for air to pass over every time the dog inhales. This functions to trap particles and potentially dangerous microbes like bacteria within the mucous in the nostrils to reduce the risk of respiratory infections. But most importantly, passing cool air over a wet tissue, allows evaporation and cooling.
Dogs with a short muzzle, have a smaller area available for air to cool within the nasal turbinates. If the dog with a short muzzle also suffers from brachycephalic obstructive airway disorder (BOAS), they also have smaller nostrils, so the air cannot flow into the nasal turbinates as quickly. They then have narrowed air passages in the throat and whole windpipe, meaning both inhalation and exhalation is slower, and requires more effort. Remember these dogs are also using more effort and energy to move their limbs than a normal dog, add to that increased heat generated by the respiratory muscles having to work harder too.
So, not only do brachycephalic breeds over-heat more quickly because simply walking and trotting they use more energy than a longer legged, longer nosed dog, but they also have a significantly less effective cooling mechanism because of their short nose. At the talk by Dr Fischer we were told that in Germany, Bulldog owners are advised to actively cool their dog as soon as ambient temperature exceeds 25oC. French Bulldog owners are advised to actively cool their dog above 28oC.
Altering bone, alters a dog’s risk of developing heat stroke.
Bone and insulation
The wonders of bone continue. People often think of a bone as a permanent, fairly fixed body structure. You suffer growing pains during adolescence whilst your skeleton grows and develops, then you reach your adult size and that’s about it. However, bone is continually growing, developing and changing right up until you reach middle age. Bone reacts to the stresses placed upon it. If you do a lot of high impact activity like aerobics, running, jumping or cross fitness, your bone responds to this by strengthening and changing in structure. If you are, as Dr Fischer put it, a “sofa pumpkin” (aka a couch potato, but we MUCH prefer this term!) and subject your bone to very little strain and load, bone will become less dense as you age.
How does this affect body insulation? Active bone, releases a hormone called osteocalcin. This hormone alters how cells respond to insulin in both mice, and humans. A failure to respond to insulin causes type 2 diabetes mellitus. In humans this condition is associated with a sedentary lifestyle, excess intake of carbohydrates and obesity. Mice with no osteocalcin are more likely to develop both type 2 diabetes and obesity. Mice with high levels of osteocalcin are almost resistant to developing type 2 diabetes and obesity. The link between a sedentary lifestyle and an increased risk of both obesity and diabetes mellitus type 2 is partly due to bone.
So, a dog doing very little high intensity exercise that involves stressing and loading the bone (just walking and mainly being a ‘sofa pumpkin’) is at greater risk of becoming obese and developing type 2 diabetes. The obesity is a big problem. An increased layer of fat under the skin acts as insulation, so the dog loses less heat into the surrounding air. This means the dog needs less energy to maintain body temperature (dogs typically use around 70% of their energy intake from food just to maintain their body temperature, this increases if the dog is in a cold environment). So if their diet remains the same, they will be consuming too many calories for simply maintaining their body, so the excess energy will be stored as, you guessed it, more fat. This becomes a vicious cycle.
Whilst dogs lose heat through their respiratory tract, in particular using their nasal turbinates, they also lose heat through conduction and convection into the air and the floor in contact with their skin. If they are overweight the extra fat beneath the skin reduces this heat loss. These dogs are then heavily reliant on using their respiratory tract to cool, so you might notice they pant more than a less overweight dog, at lower ambient temperatures. Obese dogs are at increased risk of heatstroke, and are more likely to die from the condition.
How do bones impact activity?
Anyone who has ever experienced osteoarthritis or a fractured bone will know the answer to this question all too well. A painful joint or bone is horribly unpleasant, so we avoid using it. Not using a bone, especially a bone in the leg, will impact loading on that bone. This impacts bone strength, the release of osteocalcin, and also the health of cartilage that lines our bones in joints. Cartilage relies on loading to supply nutrients to the deeper layers, no nutrients, the cartilage thins and calcifies into new, abnormal bone. This contributes to osteoarthritis development.
So the less you use your bones, the weaker they become, and the more likely it is that you will develop painful joint disease. This makes you less inclined to use your bones, because they are painful. Which starts the cycle all over again.
So what should we do?
Body composition and skeletal health is hugely important for your dog’s overall health and welfare. Musculoskeletal disorders, including osteoarthritis, are among the top three causes of death in dogs, alongside cancer and neurological problems.
Look critically at your dog. Can you see their ribs or can you feel them? If not, your dog could probably lose some weight. This will also allow them to be more flexible and active. Being more active, will prolong their bone and joint health. Ultimately, this will reduce their risk of heatstroke.
If the wonder of bones has gripped you as much as it did us, we thoroughly recommend Dr Fischer’s book, Dogs in Motion. A sneak preview in the video below.
The heatwaves currently sweeping the UK, Canada and Japan this year have already resulted in the loss of both human and canine lives. The UK’s Environmental Audit Committee warns the frequency of such heatwaves is likely to increase in the UK , with the number of human deaths potentially increasing three fold. We have been warned that society needs to be “better prepared” for such heat, so here at Hot Dogs Canine Research we’re starting now!
Firstly, some “false news”
Ice cubes are not dangerous to dogs, provided they are used appropriately. There has been a lot of misinformation on social media regarding ice cubes, with a recent story suggesting that a vet warned owners ice cubes could kill their dog. This story has been misinterpreted. A dog with heatstroke should not be cooled with ice. We’ll come on to why later in the post. A dog in a heatwave, getting fed up with the hot weather, can absolutely have the odd ice cube. Or iced dog food popsicle, or frozen cream cheese lick mat! A fit and healthy dog, will not suffer any ill effects from consuming frozen food or ice cubes, in the same way that we suffer no ill effects from ice lollies. They should be provided in moderation, and they should not replace constant access to clean, fresh, cool water.
Cooling a playful dog
If you have a dog that is a little too stupid to realise it is too hot to play (see Stevie below for a classic example), you should consider active cooling methods to stop them overheating. Stevie is partial to a hosepipe. He gets to play in the jet of water for a couple of minutes, then the hose is switched off. Dogs have died from water poisoning, so it is important to not encourage your dog to drink excessively when it is hot. Avoid lots of toy chasing/retrieving, or allowing dogs to snap at running water for prolonged periods. Stevie gets a couple of minutes, then the hose is switched off – moderation is the key.
Swimming or sitting in water is also a great way of keeping cool. Dog proof paddling pools are great – the inflatable ones often succumb to punctures from claws – and some dogs will choose to just climb in and lie down. Swimming in open water is not only a great way to cool down, but also excellent exercise for hot dogs. Sadly during summer blooms of blue-green algae can render small lakes and ponds dangerous to dogs, so keep an eye out for warning signs and learn how to recognise the problem here.
Cooling coats and mats are becoming increasingly popular, but be aware there is no robust evidence to support their use, yet. We are in the process of evaluating one, so watch this space for updates!
Cooling a hot dog
If your dog is hot from exercise, you may want to consider actively cooling them on a regular basis. Dogs do not sweat (apart from their paws) so they rely on panting, and losing heat from their body through radiation into the environment, or conduction to colder surface or liquid. There is some evidence that dogs may continue to overheat AFTER they have finished exercising – our study investigating cooling in dogs supports this finding in canicross dogs – so the risk of heatstroke doesn’t end just because the exercise had.
There is very little robust scientific evidence to support any specific cooling method.
Studies have been done cooling dogs with heatstroke, but none to date simply cooling dogs post exercise. Our advice at the moment, is to first know your dog and trust them. If they are dragging you to the nearest puddle, lake or water bucket, chances are they are looking to cool themselves down. Let them. Most dogs will get out when they’re comfortable.
If like Murphy here (on the paddle board), your dog likens water to a dog eating monster, you may struggle to get them into a paddling pool or stream for a quick dip. Applying water with spray bottle, or sponge to the legs, inner thighs, belly and neck is the next best advice. Dogs with a heavy coat and become water logged, and can take an age to dry, so targeting the areas with less hair, like the belly and thighs, can provide some relief, without causing too much of a wet dog smell.
Allowing your dog to drink is incredibly important. Dehydrated dogs get hotter when exercising , and are at greater risk of heatstroke. If your dog has been unwell, especially with diarrhoea or vomiting, they are more likely to be dehydrated, so ideally don’t allow them to exercise until they are fully recovered. Allowing your dog to drink tap water (typically between 10-15oC depending on the time of year) will help them to cool, and maintain hydration. Again you need to know your dog. If they are likely to drink a 2 litre bowl dry in one sitting and ask for more, you may need to stagger their intake, but most dogs will drink as needed.
Cooling a dog with heatstroke
Again, there have been several stories on social media regarding cooling dogs with heatstroke, very few backed by up solid science.
A conscious dog with heatstroke was found to cool quickest when immersed in water at 15-16oC. These dogs climbed out of the water baths themselves once they had recovered.
The comatose dogs cooled much slower than the conscious dogs, largely because they stopped panting. Their rate of cooling was similar in water temperatures ranging from 1 to 16oC, however, two of the dogs cooled with ice water died immediately following immersion in the water. These dogs started shivering once they were place in the ice water bath, which could have caused further elevation in body temperature contributing to their deaths. When placed in water above 18 degrees, the dogs cooled more slowly.
In an emergency situation, the current best available advice for treating heatstroke is to continuously pour tap water over the dog, with as much air movement as possible, a fan or air conditioning is ideal. Do not delay getting the dog to a vet, especially if they are already comatose. These dogs need emergency care to maintain their blood pressure and try to save their brain, kidney and liver function. Cool the dog quickly, then transport them whilst maintaining air flow (windows down or air con on in the car) to the nearest available vet. Try not to lay things over the dog, like wet towels, as this could restrict air flow to the skin and could reduce heat loss.
Once heatstroke has occurred, rapid action is required. If the dog is still conscious, allow them to drink a little, and cool them with tap water. Seek veterinary care quickly. If the dog has already lost consciousness, every single second counts. Rapid cooling, then ideally continue cooling on route to the vet.
If its hot outside, chill out! Lie back, put your feet up, and enjoy a nap like Monty here.
Hopefully by now, most people have seen the warnings that dogs die in hot cars. They die of heatstroke because trapped within a car, with little or no air flow, they get hotter and hotter. Once their internal blood temperature exceeds 41oC their internal organs become damaged and begin to shut down. This can take minutes.
But hot cars are not the only reason dogs die from heatstroke. Increasingly, hot countries are reporting that exercise is the major reason dogs get taken to the vets with heatstroke. Now in the UK we’ve been lucky. Traditionally, the UK doesn’t see much hot weather, and when we do, it usually doesn’t last long before we get rain, wind, sometimes even the odd summer snowfall!
But this is changing. Climate change is increasing the number and frequency of abnormal weather events. Look at 2018, at home in the Midlands in March it was -7oC. Three months later it hit 32oC on my driveway. Three months is 90 days. Heat acclimatisation takes around 60 days. I remember de-icing the car on Easter weekend, so before the prolonged period of heat hit, we didn’t have 60 days to acclimatise to the heat, and neither did our dogs. Already there have been reports of dogs presenting to veterinary practices suffering from heatstroke following exercise, one dog lost their life following a walk in the heat.
Heatstroke happens when exercising dogs get too hot and stay hot.
Dogs and temperature
Unlike horses and people, dogs can’t sweat.
Unlike horses and people, dogs come in an enormous range of sizes, colours, coat types and length, breeds and personalities. Ok, people and horses are also pretty variable, but you don’t often see a x40 difference in body weight like you do in dogs.
Because dogs can’t sweat, and because they are so variable, there is NO SAFE TEMPERATURE. In our research we saw dogs reaching a critical temperature (over 40.6oC and up to 42.5 oC when measured with an ear thermometer) at every race we attended over a two year period. At every race. Some races it was snowing, the hottest race was 15.4oC. We’ve spoken to canicrossers (people who run with their dog in harness) who have seen dogs collapse from heatstroke with snow on the ground (on-going project so no reference yet!). Yet we’ve also seen dogs competing in long races in the middle of summer crossing the line safely.
There is no easy way to predict which dogs will overheat.
You need to know your dog. Some dogs will tell you when they’ve had enough. They’ll lie down, or seek shade, or just flatly refuse to move! But some dogs will run until they drop, so they need to be managed with exercise only in the cooler mornings and very late evenings.
A cautionary tale
Danny lost his beautiful dog Brodie in June 2018. The temperature was 19oC. Brodie wasn’t working hard.
This is what he was doing before he collapsed; listen to Brodie’s breathing at the end of this video, something wasn’t quite right: Brodie training
Brodie collapsed shortly after this video was taken. Tragically he died from heatstroke.
Danny has kindly allowed us to share Brodie’s story, because like us, he would like to see canine heatstroke become a thing of the past. Heatstroke kills dogs. Veterinary hospitals report mortality rates of up to 63% in dogs with heatstroke.
Your dog won’t die from a missed walk, or run or training session. If they get heatstroke: flip a coin. Heads you win, tails they lose.
Radiating heat into the air around them – the hotter the air, the more humid the air, the less this happens.
Conducting heat to their surroundings – if the ground is hot this won’t happen.
PANTING! Air in the lungs is moistened, meaning water evaporates as the dog pants. If the dog can’t move enough air, or if the dog is in a humid environment, this becomes ineffective.
So if it is hot and humid dogs will struggle to cool.
But even if it’s cold and dry, if your dog can’t move air, their main cooling mechanism isn’t working.
Panting, some key facts
In order to pant, dogs need to be able to move air. Anything obstructing air flow, will limit the effectiveness of panting and therefore cause the dog to overheat more quickly (see below for respiratory disease).
Laryngeal paralysis (see below)
Any respiratory disease, or heart disease that affects normal breathing.
In order to lose heat through panting, dogs need enough water in their body to moisturise the air. A dehydrated dog will conserve water and produce less saliva, and not moisturise the air in their lungs as much as a well hydrated dog. Unsurprisingly, they get hotter quicker when exercising.
Anorexia (not eating)
Being in a hot environment
Urinating more frequently (diseases like diabetes, Cushings, hypothyroidism, renal disease can all cause this)
Not being given enough to drink or something nice to drink
Anything that could make your dog even slightly dehydrated could increase their risk of heatstroke if they are exercising. The same as people!
How do I know if my dog has a respiratory condition?
Usually, this is fairly obvious. If you’re sat on your sofa watching television, can you hear yourself breathing? No? Good, this is normal! Noisy breathing happens when there is turbulence in the respiratory tract. This could be a narrowing, a flap of tissue, or liquids like mucous or pus. Narrowed airways may cause wheezing, or whistles. The classic noise is snoring. If you can hear your dog breathing when they are at rest (and awake), this isn’t normal.
However, this isn’t always the case. My family dog Holly (the Goldie here) had laryngeal paralysis (LP). This is a disease one respiratory specialist vet described as “something that can be diagnosed whilst walking past a dog in the street”. They’re normally noisy.
Holly wasn’t a noisy breather. She panted quite a lot but never made ANY noise. I am a vet, and I missed it. She started collapsing on walks. She would go very pale, collapse, and then about 5 minutes later get up and be fine! I checked her, found nothing. Checked her again, found nothing. Then one day I was there, her heart rate was over 300 beats per minute and that’s not normal! So I referred her to a cardiologist thinking she must have a heart problem, they eventually examined her airway with an endoscope and found her LP. Her diagnosis was made almost by accident.
Because we then knew she had a respiratory problem we were careful with her. We kept her cool, we kept her walks short, we kept her weight as low as we could. Because of my background, I knew she was at an increased risk of heatstroke, so I made sure she wasn’t put at risk.
If you are worried about your dog, get them checked by a vet. If they find nothing, but you are still worried, get them checked again. Don’t be afraid to ask for unusual things. If your dog’s problem happens during or after exercise, ask if you can walk them in the car park and have them examined during and after exercise.
If you know, or suspect, that your dog is suffering from any kind of respiratory problem, be extra careful. Keep your dog cool in the warm weather and don’t risk exercising during the heat.
This applies both to your ability to accurately use the thermometer you have chosen (see below for tips on some of the more sensitive ones), and also to interpret the reading in front of you.
What is a normal canine temperature?
This isn’t an easy question to answer. Google normal dog temperature and you will find a huge variety of temperature ranges reported by various sources. When you look at the range, does it tell you who established it and in what population of dogs? So far we have only found one source that answers those questions, and it was a German study, using 62 healthy dogs presenting to a veterinary hospital. The range they suggest is “normal” for a dog in the vets is 37.2 to 39.2°C (Konietschke et al. 2014). Keep in mind, these were dogs in the vets, so your dog at home in a non stressful environment is likely to be at the lower end of this limit.
Consider your dog’s state when you take their temperature. Are they excited, have they just been fed, have they just been walked/run/chased the cat, have they just spent the last hour lying in front of the fire?
After exercise, you dog’s temperature could be anything from low (if they got very wet in cold weather), right up to around 42.5°C – this is seriously hot. If you dog’s temperature is over 40°C after exercise, considering cooling them or at least check it again after 5 minutes. If a dog’s temperature remains over 41°C for any length of time this is when heatstroke becomes a very real (and possibly fatal) possibility.
If you’re going to go to the trouble of monitoring your dog’s temperature, make sure you understand the risks and limitations of the thermometer you choose to use.
Mercury glass thermometers
These are the traditional thermometers you may remember from science classes at school. They are rarely used in the UK anymore, due to the very real risk of the glass breaking and mercury poisoning! (Emily – I can remember an order of 10 mercury glass thermometers arriving completely smashed, and having to close the vet practice I was working in for the day, evacuate all staff, clients and patients so it could be professionally decontaminated!)
If you only have access to this type of thermometer, you need to be aware of three important things:
Firstly, you’ll need some lube. You can’t ask your dog to hold this under their tongue for a minute, so it’s going into the other end I’m afraid! Forget lubrication, and this is the last time your dog will ever let you anywhere near their bottom.
Secondly, once you’ve found some lube, you need to shake the mercury back into the bulb. Otherwise you won’t know if the measurement you get is today’s temperature, or the last temperature recorded.
Finally, you do need to leave them in for at least a minute. Remember there is risk of breaking the glass, so seriously consider if this type of thermometer is worth the risk.
Digital predictive thermometers
There are now far more common in both human and veterinary practice. The major advantage of these thermometers is speed. Not as accurate as simple digital thermometers (the hints in the name, predictive), but readings usually in under 10 seconds.
If you are looking for a cheap, reliable, safe and accurate option for monitoring temperature, this is your best bet.
Things to remember:
I’m going to say it again, LUBE.
Often these come with disposable plastic thermometer covers to help reduce disease transmission. It’s up to you if you want to use them, single use plastic waste should be avoided where possible, so if you opt to go down the sustainable route remember to disinfect your thermometer after every use.
If you can, go for the models with a flexible probe, if you dog sits down, they’ll thank you!
So far, we’ve found these to be the best alternative to rectal thermometers in terms of both accuracy and tolerance. You do need to use a veterinary model, so thats either the Vet-Temp or the Pet-Temp, which means you’re looking at around £100+ for the thermometer and you definitely need a supply of probe covers. Ear wax completely blocks the thermometer’s sensor so you can’t scrimp on using a new probe cover each time I’m afraid.
Ear thermometers are not as accurate as rectal thermometers. There are more things to go wrong: correct positioning, ear wax, hairy ears.
If you are going to use an ear thermometer, train your dog to accept ear handling and gradually introduce the thermometer. We’ve found most dogs tolerate the thermometer really well, but it does beep loudly.
Also, if you’re going to use an ear thermometer, use an ear specific normal temperature range. We suggest 36.6-38.8°C (see references below).
If something sounds too good to be true, be wary. Human medics and nurses have found these thermometers to be both accurate and safe, reducing the risk of disease transmission between patients as they require no physical contact with the patient. Sadly so far the situation in veterinary medicine is very different. Animals are typically covered in fur, so obtaining an accurate temperature by measuring the animal’s skin surface temperature isn’t currently possible.
So far papers have explored using the eye (Kreissl & Neiger 2015), various anatomical sites including the ear, gums and hairless skin near the rectum in cats (Nutt et al. 2015) and the muzzle and forehead regions in dogs (Omóbòwálé et al. 2017). None of these papers support using NCITs in a clinical setting.
We have just finished a study comparing NCITs to rectal temperature in cats and to ear temperature in dogs, watch this space for the final results!
Temperature sensing microchips
Underused in my humble opinion! No, they don’t report the same temperature as a rectal thermometer, but guess what, a rectal thermometer doesn’t report the same temperature as blood temperature so it’s a compromise (Greer et al. 2007).
To me, your dog legally has to be micro-chipped (UK), why wouldn’t you have one that gives you the option to also monitor temperature?
You can pick up a temperature reading microchip scanner for around £55 on Amazon (Halo scanner) – incidentally, if you travel with your dog, this is worth buying anyway, with your own chip scanner you can check your dog’s chip is reading fine before you set off, and if you pack your scanner you know you can locate it at customs should they have a problem! The Halo scanner has the added benefit that if you regularly connect it to the on-line database, if you scan an animal reported as lost or stolen, this will flash up when you scan the chip. So if you regularly come across lost dogs, having one of these in your car can be useful.
These scanners are really easy to use, you just squeeze the handle (where it says Halo), wave them over your pet’s chip, they beep when they’ve found it and display the temperature.
Summer is a great time to get out and about with your dog. But dogs don’t tolerate the heat as well as their owners. When people get hot they start to sweat, but dogs are only able to do this through the pads on their paws. Dogs instead rely on panting as their main method of cooling.
But panting can only control body temperature up to a point. As temperatures and humidity rise, panting is no longer able to cool the dog. This leads to an increased risk of heatstroke in dogs, which is potentially fatal. It’s worth remembering that it can take around two months for a dog to acclimatise to high temperatures so it is important not to become complacent.
What is heatstroke?
Like humans, dogs can develop heatstroke in two main ways. Environmental heatstroke occurs following exposure to high temperatures, the classic example being a dog left in a hot car. Exertional, or exercise-related, heatstroke occurs during or following exercise and can happen at any time of the year. Heatstroke happens when an animal is no longer able to cool itself and its body temperature can no longer be controlled. When the dog’s body temperature exceeds 40℃, irreversible changes start to happen such as brain damage and multiple organ failure.
Every year, there are numerous reports of dogs dying in hot cars. Cars can get hot surprisingly quickly with internal temperatures reaching 40℃ within just ten minutes of being parked in full sun. Simply exercising or playing in warmer weather can also lead to heatstroke in surprisingly short periods of time, just a ten minute walk could be too much. Dogs that are working or competing in hot conditions are also at risk, so making sure they are kept cool is key.
Certain factors put some dogs at a higher risk of heatstroke. Brachycephalic (short faced) breeds, such as pugs and boxers, are more likely to suffer, as are animals with respiratory disorders. Male dogs and those with darker coats also tend to get hotter in warm weather.
Reducing the risk
Don’t leave your dog in the car and never leave dogs unattended. Even in the shade, car temperatures can increase quickly and as the sun moves and shade disappears the internal car temperature will rapidly increase. Leaving windows partially open has little effect on car temperature. If you are stuck in traffic or travelling, have the air conditioning on to keep the car cool and make sure windows are shaded from direct sunlight. Ideally, leave your dog at home in hot weather.
Try to exercise your dog in the cooler parts of the day. Avoid any strenuous exercise in the heat. And make sure you supervise activity – your dog may not know when to stop. Instead of exercising in full sun, try brain games in the house or walking in the shade, such as woodland.
All dogs need access to cool water and shade to keep their temperature down. If your dog is unfit, obese or suffers from a respiratory disorder be particularly careful exercising in hot or humid conditions.
As the weather becomes more unpredictable, the risks of being unprepared increase. Even in winter, dogs can be at risk with temperatures getting warmer than expected. The continuing changeable weather also makes it challenging to acclimatise to the heat, making sudden, unseasonal hot spells even more dangerous.
Signs of heatstroke
Heatstroke can happen very quickly, starting with rapid breathing, lack of energy and decreased urine production. This can very quickly escalate to heavy panting, bulging eyes, and the tongue appearing excessively long and dark red. Collapse (leading to seizures or coma) and vomiting and/or diarrhoea can follow.
Both cooling your dog, and getting to the vet as quickly as possible are the two key ways to increase the chance of survival in heatstroke cases. Avoid using ice or very cold water as this can cause blood vessels on the skin surface to constrict and reduce effective cooling. It can also cause shivering which can create more heat from the muscles. Key areas to cool are the neck, abdomen and inner thighs with lukewarm water or water-soaked towels. It is important that you do not over cool your dog, as this can lead to shock – a lack of blood supply to vital organs – so using lukewarm water is important.
Out and about, cool surfaces, shade, air conditioning in cars and fans can also aid cooling. Even if the dog is cooled, veterinary treatment is still key to allow more targeted treatment and monitoring to occur. Heatstroke has been reported as fatal in 39-50% of dogs but those surviving more than 24 hours have a good chance of making a full recovery.
We have started this blog to share our research findings with the wider dog owning, dog working, and dog competing community. Apologies for the lack of content at the moment, but we hope this will soon change!
For now, here are some of our recent research findings and publications in an openly accessible format, along with links to the published works (which are sadly mostly behind paywalls):
Anne presented our preliminary findings on “Non-invasive temperature monitoring of canine athletes” at the Canine Science Forum in 2018.
Anne also presented “Investigating non-invasive methods of monitoring body temperature in in a range of domestic species” at the British Society of Animal Science annual conference in 2019.
Emily presented initial findings from the Hot Dogs VetCompass project to the British Small Animal Veterinary Association annual congress in 2020 (available to watch here).
If you have any concerns about your dog’s health please consult your veterinary surgeon immediately. This site is designed to provide information and share knowledge regarding heatstroke, but is no substitute for veterinary care for your dog
Sharing our research into canine heatstroke and heat related disorders.