Cats, like humans, are thermostats and therefore need to maintain a constant body temperature to survive. Unlike snakes and bears, they only hibernate in winter. Regulating the cat's body temperature is the thermoregulatory center (hypothalamus - preoptic area) located in the brain, similar to the regulating panel of an air conditioner.

The thermoregulatory center has a temperature known as the “preset value” (normal body temperature), which is innate. In humans, the pre-set is 36.5-37.5°C. Kittens are born with a pre-set of 34.7-37.2°C and remain at 36.1-37.8°C for a week after birth. however, adult cats over the age of 1 year have a higher average body temperature than humans, which is roughly 37.7-39.2°C. Because of this difference in body temperature, humans feel warm when they hold a cat.

When the body temperature deviates from the preset value by 1°C, the thermoregulation system will be activated and the body will restore the body temperature to the normal level through various mechanisms. It is like an air conditioner automatically detecting temperature changes. So how does a cat regulate its body temperature?

Heat transfer occurs continuously between the cat's body and the external environment. These heat transfers are mainly in four ways, namely “conduction”, “convection”, “evaporation” and “radiation Conduction”, ‘Convection’, ‘Evaporation’ and ‘Radiation’.

Conduction is the transfer of heat from the surface of the human body when it comes into contact with a liquid or solid at a temperature lower than the body's temperature. When the contact is with an object hotter than the body temperature, heat is transferred to the body in the opposite direction.

For example, it is easy to understand that when you touch an ice cube with your fingers, the coolness you feel is “heat loss”, and when you suck hot ramen noodles with your tongue, the feeling is “heat gain”. When you sit on the toilet in winter, your buttocks feel cold because the toilet quickly takes away your body heat through heat transfer.

Convection is the transfer of heat energy when the surface of the body comes into contact with a gas that is cooler than it is. When the body comes into contact with a gas that is hotter than the body temperature, instead heat energy is transferred into the body.

The cool feeling you get when you open the refrigerator is called “heat loss” and the warm feeling you get when you blow hot air from a hair dryer is called “heat gain”.

Vaporization is a phenomenon in which a liquid (water/alcohol) carries away heat through vaporization when it evaporates from the surface of the body.

With evaporative heat, imagine the cool sensation of a fan blowing on a sweaty body. Sweat (water molecules), which absorb heat from the heated body, is carried away by the fan's airflow, resulting in rapid heat loss and a “cool” sensation.

Radiation is the release of heat into the environment in the form of electromagnetic waves, also known as thermal radiation.

Even if there is no direct contact and no wind blows, you feel warm when you put your feet on the stove because the infrared heater radiates heat outward to your feet. Perhaps the term “human breath” refers to the subtle radiant heat we feel when someone is near.

After learning about the four types of heat transfer, we will see how cats utilize these principles in their lives.

How do cats lower their body temperature in the summer to cope with the heat and avoid the risk of heat stroke? Let's look at examples from life.

Summer Thermoregulation and Conduction

Cats will use heat conduction to lower their body temperature through direct contact with liquids or solids. For example, they will lie down inside a cool sink or belly up against a marble floor. This is a good example of how cats understand the physical law of conduction.

Cooling products for pets, such as gel pads, also utilize the principle of conduction.

Summer Thermoregulation and Convection
Cats use "convection" of heat transfer generated by continuous contact of gases to lower their body temperature. Specifically, they will stay in front of the air conditioner outlet where the cold air blows out, etc.

Humans have sweat glands all over their bodies, so even a tepid breeze will take away the evaporative heat and feel quite cool. But cats do not sweat, so when they are exposed to the warm summer wind, it is like being blown dry by a hair dryer. This may be why cats don't like electric fans very much.

Summer Thermoregulation and Evaporation
Cats use the "evaporation heat" generated when liquid containing body temperature evaporates to lower their body temperature. Specific methods include licking their fur, moistening the surface of the body and exposing it to the wind, increasing saliva secretion and breathing vigorously, etc. This breathing method is also called "panting breathing", equivalent to where humans sweat when they are fanned.

Unlike humans who sweat all over their bodies, cats covered with fur can only sweat from their paw pads. The reason why cats are more susceptible to heat than humans is that the body surface area that generates vaporization heat is much smaller than that of humans, and it cannot dissipate heat efficiently. Therefore, the following differences in body temperature may occur. When humans feel "a little hot...", cats may feel "very hot!" with difficulty breathing, so be careful.

Cats' panting is related to the "carotid body" in their necks, which is a sensor located in the thick blood vessels in the neck (Fadic, 1991). When this sensor is damaged, cats cannot stick out their tongues to breathe even if their body temperature reaches 40℃, so it is believed that it plays a role in detecting the concentration of oxygen and carbon dioxide in the blood, causing panting. Cats rarely stick out their tongues, so when they pant, they are either very hot or have some disease.

The following is a list of diseases that cats may have when they pant without exercise and in the heat, for reference only. Some underlying diseases may be involved, such as "nasal congestion", "respiratory system disease", "circulatory system disease", etc. Please consult a veterinarian.

Possible diseases for pulseless panting

Feline infectious peritonitis

Feline infectious anemia

Rhinitis

Sinusitis

Epistaxis

Heatstroke

Ingestion of foreign objects

Heartworm disease

Tick disease

Heart failure

Patent ductus arteriosus

Tetralogy of Fallot

Pulmonary artery stenosis

Ventricular septal defect

Hemolytic anemia

Malignant lymphoma

Angiosarcoma

Metabolic acidosis

Respiratory system disease

Toxic ingestion

Obesity

Summer Body Temperature Regulation and Heat Dissipation
Cats use natural heat dissipation when lowering their body temperature, which refers to the heat dissipated from the surface of the body. For example, they hide in the shade or under the bed to avoid direct sunlight, open their bodies to increase the surface area, or use their tongues to concentrate blood and stick out their tongues to use heat dissipation to regulate body temperature.

When cats feel hot, the blood gathered in their internal organs moves to the surface of the body. This shortens the distance between the heat-filled blood and the outside world, making it easier for heat to dissipate from the blood. In addition, by exposing relatively thick blood vessels such as the armpits, neck, abdomen, and thigh roots, the heat dissipation efficiency can be improved. When cats stretch their limbs in the heat, it becomes a summer landscape called "cat openness" because of this.

For breeds with longer hair, "summer haircuts" are sometimes implemented in the summer to improve heat dissipation. Just like humans change from wearing down jackets to wearing T-shirts, but compared to dogs, cats may move when trimming, so we often see people shaving cats' hair with a razor so short that the skin can be seen. If cats are left in this state all the time, the following disadvantages will occur, so you need to pay attention.

Disadvantages of shaving cats

In the case where the outside temperature is directly transmitted to the body, in hot weather with a body temperature of more than 37°C, the temperature that should be blocked by the hair will directly enter the body, increasing the risk of heat stroke in cats.

Hair should block ultraviolet rays, but now it is more susceptible to ultraviolet rays, making it easy to suffer from diseases such as sunburn and ultraviolet-induced skin cancer.

Hair should protect the skin from external forces, but now the hair is in direct contact with the skin, so it is easy to be scratched or cut.

In a multi-cat household, if only one cat is shaved, its body temperature will be different from that of the other cats, and it will become more difficult to manage the indoor temperature.

Grooming is a daily activity for cats, and the lack of hair that should be there may become a source of stress for cats.

Because the skin on the abdomen is directly exposed to the outside air, it is easy to get cold, and the body temperature drops, causing the body to have to make unnecessary temperature regulation, which may lead to adverse reactions such as diarrhea and autonomic nervous system disorders.

Many cats will naturally reduce the amount of hair before the arrival of summer, that is, their molting period. However, no cat will completely lose its hair during the molting period and become a bald sphinx cat. Therefore, it can be seen that cats make sense to retain their hair to a certain extent. If long-haired cats are simply trimmed to a medium length, it can be said to be "helping cats through the molting period", but shaving the scalp to expose it is an example of "too much is as bad as too little".

The "strange network" of heat dissipation in the brain

The basic strategy of cats to avoid high temperatures is to avoid direct sunlight, not to move unnecessarily, and to stay still. In addition, there is an ingenious mechanism in the cat's brain that prevents nerve cells from overheating, which helps prevent heat stroke. This is a magical organ called the "venous network", which does not appear in primates (such as humans and monkeys).

The carotid artery refers to the thick, oxygen-rich artery that connects to the brain, and the cavernous sinus refers to the network of blood vessels with a lower oxygen concentration distributed in the brain. The two cross near the center of the brain, but the mandibular artery that branches from the carotid artery suddenly forks when passing through the cavernous sinus, increasing the contact area with the cavernous sinus. This is to effectively cool the blood structure by increasing the contact area between the hot arterial blood and the cold cavernous sinus.

The cooled venous blood at the tip of the nose collects in the cavernous sinus, just like pouring into a swimming pool, crossing with the artery and moderately cooling the blood. The cooled arterial blood then enters the brain to provide oxygen and nutrients to nerve cells. In other words, the venous network and cavernous sinus act as a radiator in the brain.

Dogs have only one venous network, while cats have two venous networks, one on the inside and one on the outside. There are many reasons why cats have fewer cases of heat stroke than dogs, but the function of this "venous network" may be one of them.

What do cats do when it's cold?
When temperatures rise in winter, more heat is lost to the environment, so the lowered body temperature needs to be restored to normal. To put it bluntly, it means "surviving the cold." So how do cats keep warm in winter, keeping themselves warm and avoiding hypothermia? Let's think about it about the heat transfer methods we saw in the previous section.

Winter Thermoregulation and Activity
Cats use the popular method of heat, that is, direct contact with liquids or solids to increase their body temperature. Specifically, they will "huddle" with other cats with similar body temperatures, or sleep on pet heaters, etc.

Humans, capybaras, and monkeys like to soak in hot springs, but cats don't like to get wet, so they don't enjoy bath time. Instead, they will lie on their owner's computer and enjoy the warmth of the bath, sometimes interfering with their owner's work.

Winter Thermoregulation and Convection
Cats use heat transfer generated by continuous contact with air currents to maintain their body temperature, which is called "convection." Specifically, they will hide under the eaves of the house to avoid the cold wind or enjoy the warm and balmy wind in front of the computer fan. Before the cold season arrives, they will make their fur thicker and make their skirts to avoid cold wind, which can also be said to be a method of temperature regulation using convection.

Preventing cold wind "convection" from consuming your body heat is the best strategy in winter, but it can be life-threatening in some places. Specifically, it is in the engine compartment of a car parked outdoors. It is said that there is an increase in "cat noises coming from the engine compartment" in winter. It's a good thing drivers are aware of this, as some cats have had unfortunate accidents with engine belts getting caught.

In the cold season, always tap the engine compartment to confirm whether there is a cat inside.

Winter sleep regulation and evaporation
Cats must detect the "heat of vaporization" when hot liquids evaporate to maintain body temperature. Specifically, they should close their mouths, switch to full-nose breathing, and be careful not to get their bodies wet.

One of the reasons cats hate dry fur is that evaporative heat takes away heat and causes hypothermia. The Libyan Desert Cat, the ancestor of cats, lives in desert areas where the temperature difference between summer and winter is extremely large. For these animals living under such conditions, evaporative heat in winter is said to be a great enemy. When the temperature of the newborn is low and the body is dry, the evaporative heat evaporates, sometimes leading to death.

Domestic cats, descendants of the Libyan wild cat, no longer live in the desert, but their ancestors' hydrophobia is still present in their DNA. Thus, they don't like dryness regardless of the season. This is also one reason why cats are interested in swimming pools or hot springs.

Winter insomnia and sleeplessness
Cats use the heat dissipated from the surface of the body to control heat, such as curling up to reduce the heat or burrowing into the quilt. These behaviors can reduce body heat. In addition, they burrow into the side of the heater, etc. to increase the heat absorbed by the body. These behaviors are all to increase the heat absorbed by the body.

When a cat feels, its body's blood vessels will concentrate from the surface to the inside, trying to reduce the loss of cold from insomnia. On the contrary, in hot climates, cats will curl up into a "cat sleeping position" to keep warm by contacting relatively thick blood vessels in the armpits, neck, abdomen, and shoulder bases, which improves their breathing efficiency.

Cats grow slightly thicker fur in winter to reduce natural heat dissipation. In addition, they increase their food intake to obtain the energy needed to maintain body temperature and increase subcutaneous fat to improve thermal insulation. For cats living in air-conditioned rooms, it is necessary to be aware that the increase in food intake may cause them to become overweight. In addition, in homes that use heating equipment such as stoves or kotatsu, it is also necessary to be aware of the risk of fire and low-temperature burns.

β-endorphin and thermogenesis
As a well-known analgesic drug, β-endorphin may be associated with increased body temperature.

However, shivering to maintain body temperature has its limits. If the temperature outside is too low, or if you stay in a cold environment for too long, no matter how much you shiver, you won't be able to generate enough heat, and you will eventually be defeated by the cold. For example, the photo above shows a stray cat frozen outdoors in extremely cold weather in New Hampshire, USA. It was rescued by the local fire department and bathed in warm water but was eventually euthanized due to exhaustion.

In snowy northern areas, similar tragedies may occur if cats are allowed to roam freely or get lost. Please make sure the doors and windows are closed and prepare warm beds to make the cat lose the desire to go out.

Body temperature regulation in kittens
Kittens regulate their own body temperature and can maintain the same body temperature of about 38℃ as adult cats from the age of 7 weeks. Before that, kittens are not very good at raising or lowering their body temperature, so they must pay attention to heatstroke and hypothermia.

The standard body temperature of newborn kittens is as follows:

1 week old = 35.5℃～36.7℃

2 weeks old = 37.2℃

3 weeks old = 37.8℃

Kittens in cold environments

Before the kitten is 2 weeks old (14 days after birth), if it is separated from its siblings or mother cat and loses its heat source, its body temperature will drop at a rate of 0.02℃ per minute. The same change will also occur in an environment of 23～25℃. This means that within 2 hours, the body temperature will drop by 2.4℃, so when a 2-week-old kitten (37.2℃) is separated from its parents for 2 hours, its body temperature will drop below 35℃, and the risk of hypothermia will increase sharply. By the way, the standard for hypothermia is below 34.4℃ at birth, below 35.6℃ at 3 days old, and below 37.2℃ at 7 days old.

The above is a discussion about the environmental temperature of 23～25℃ that humans feel comfortable with. If the ambient temperature reaches extremely cold below freezing, the risk of hypothermia increases further.

For example, at -15 degrees Celsius in Siberia, it is estimated that the body temperature of a kitten at 10 days of age drops by 0.2 degrees Celsius/minute and at 40 days of age by 0.1 degrees Celsius/minute. In any case, hypothermia will occur within 10-20 minutes and the animal will eventually die. It is not until after 45 days of age that hypothermia will occur in 10 to 20 minutes and eventually die. Self-regulation of the body temperature and instinctive warming behavior allow the body temperature to be maintained above 37.5℃, which can only be achieved after 45 days of birth when the kitten can begin to shiver and raise its hair.

Rapid warming is not advisable!

When you pick up a newborn kitten, it may not be able to accept milk due to hypothermia. Although you want to restore its body temperature as soon as possible, if the temperature rises sharply, it will lead to multiple organ failure and, in the worst case, death, so be careful. Do not use a hair dryer or bathe the baby, but wrap the wet body with a blanket, etc. Allow the body temperature to recover at a rate of 1°C per hour.

Kittens in hot environments
Even newborn kittens can sense temperature gradients through the temperature sensor on the tip of their noses, and behave in a way that moves to warmer places and avoids colder places. This sensor is quite efficient and is said to respond to a temperature rise of 0.2 degrees and a temperature drop of 0.5 degrees. This is an innate mechanism that allows kittens to sense the heat radiated from their mother's body even if they accidentally get lost, making it easier for them to return to their original position. The behavior of confirming the temperature by shaking the tip of their noses left and right and the behavior of finding a warm place and sticking their bodies to it are two reflex behaviors of kittens.

Kittens lose body heat more easily than adult cats because they have less subcutaneous fat and hair. However, their ability to dissipate heat is also limited. When exposed to an extreme ambient temperature of 60°C in the desert, the body temperature of a 10-day-old kitten rises at a rate of 0.05°C per minute. After 40 minutes, the body temperature rises by 2°C, causing heat stroke and eventual death. When kittens are over 45 days old, they learn to pant and cool down their body temperature by evaporative heat dissipation, which can control the rate of temperature rise to less than 0.02℃ per minute. However, even so, kittens can only tolerate high temperatures for 1.5 to 2 hours at most, and many cats born outdoors die of heat stroke before being attacked by crows.

Survival in extreme cold
Kittens have a mechanism that is not seen in adult cats that protects them from cold environments.

When a kitten's body temperature drops to 30℃, its oxygen consumption decreases sharply. Normally, the brain will die from lack of oxygen, but kittens have unique mechanisms such as "shifting to anaerobic energy production", "changes in vascular tension", "limitation of cardiac output", and "turning off energy consumption to maintain body temperature". Compared with adult cats, kittens have a relatively high resistance to low-oxygen environments.

Miraculous Survivor Cat Lazarus

On Thanksgiving Day in 2015, a frozen kitten was rescued from the snow. The kitten, named Lazarus, was miraculously revived and became part of a rescue family.

The above video shows a kitten named "Lazarus" buried in the snow and in a dying state. After one hour of care, it miraculously revived. This miraculous resurrection may be due to the brain protection mechanism of kittens in low-temperature and low-oxygen environments.