As the coldest months of the year approach, many people worry about their pets getting too cold.
I had one query from a reader who wanted to know how to keep her Golden Retriever indoors when he wanted to sleep outside at night time. She was worried that if he was outside, he could suffer serious consequences from hypothermia.
It is true that hypothermia due to environmental chilling is a real issue: every year, thousands of wild animals die from the bitter cold in the middle of winter. It's far less of a problem for pets because we offer them shelter, but it is still a topic that pet owners should know about.
So what happens when an animal gets too cold? Regardless of the ambient temperature around them, animals need to maintain a normal core body temperature to maintain normal health. In dogs and cats, the body temperature should be between 100 and 102.5 Fahrenheit (38 to39.2 Celsius).
The body temperature can become elevated for reasons of illness, excitement, exertion and a high environmental temperature. The main reasons for the temperature falling too low are advanced, debilitating illness (e.g. as a very sick or elderly animal approaches death) or a cold environmental temperature. If the temperature continues to fall despite the body's efforts to get it to rise, then collapse, coma and death can follow.
We humans use our brains to take physical steps to protect ourselves from the cold: we wear warmer clothing, stay indoors and use external heat sources such as electric heaters to keep ourselves warm. Animals do not have the brain power to take such actions (other than finding the least cold area to shelter in), so they are dependent on humans to protect them from the cold, as well as the natural responses of their own bodies.
Some animals have evolved to have bodies that protect them particularly well: examples include the thick fur coat of Huskies, furred feet in some dog breeds, and thicker foot pads in animals from cold habitats. Some species, such as penguins, have more complex heat-retaining mechanisms, such as heat-exchange blood flow to their extremities.
Apart from these specific adaptations, the normal body of all animals is well equipped to respond to a low environmental temperature, with a number of effective physiological responses.
First, the peripheral circulation clamps down: the blood vessels on the outer parts of the body constrict. This is why people's hands and limbs look pale when they are cold (this isn't visible in pets because of their fur). The reduction in blood flow to the outer layers and extremities means that less heat is lost by radiation from the surface of the body, and heat is retained for the most important organs like the heart, kidneys, liver and brain.
Second, the heat produced by the body is increased. The most visible aspect of this is shivering: the muscles contract repeatedly at a high frequency, generating heat as they do so.. Again, it is not always obvious that animals shiver, because their bodies are disguised by their fur coats. Some animals also produce heat internally by a method known as "non-shivering thermogenesis": this uses specialized fat tissue known as brown fat. Some animals have higher quantities of brown fat, including species that hibernate, and very young animals. Brown fat can release energy directly as heat.
Third, animals make the most of their outer insulating layer: fur. As well as this varying from animal to animal (e.g. Doberman to Husky), all animals have the ability to temporarily increase the ability of their fur to insulate by making it stand on end in cold weather, creating a thicker layer of static air around their body. Even us hairless humans have the remnant of this reflex action: we get goose pimples.
Apart from just general cold, people worry about their pets getting frostbite. This happens in ultra-cold environments, like North America, when winter temperatures can be -20C or lower. In the more temperate climates of Ireland, frostbite is rare, but it is a real risk, and if dogs are exercised in snowy weather. In such conditions, it makes sense to limit their time outside, and to use foot protection (such as boots) if they are spending more than a few minutes walking on the snow.
The other big risk is simple hypothermia: again, we humans need to help our pets when they can't help themselves. Make sure your pet has shelter which is dry, drought free and reasonably warm. If in doubt, give them an insulating layer of clothing, such as a fleece-type jacket. Small pets are especially vulnerable to chilling: they have a larger surface area relative to their body weight, so they lose relatively more heat.
Some dogs can tolerate colder weather than others e.g. a thick coated working Collie who is used to living in an outhouse will thrive in temperatures lower than a cosseted fine skinned Chihuahua who spends her whole life indoors.
As for that Golden Retriever? On cold nights, he should be kept indoors, even if he doesn't want to stay. Otherwise, an insulating fleece dog coat is a useful way of ensuring that he doesn't suffer from too much chilling when he's resting in his kennel outside on warmer winter nights.