Posted on 07-05-2017
Summer is just around the corner and soon you and your pet will be looking for relief from the heat and humidity. Before discussing steps that you can take to keep your pet cool and comfortable during the warm season, it is worthwhile to recall the ways in which an animal dissipates heat from its body. This essentially involves the opposite of the methods that animals deploy to conserve body heat (see Winter Weather Hazards articles, in particular the graphs from Tufts University School of veterinary Medicine). To illustrate the differences, compare your responses to heat with those that a hair coat bearing animal uses. When our surface body temperature rises, we start to perspire; the perspiration evaporates from the body surface and the energy transfer helps cool our outer body temperature. When a breeze blows, the air currents also aid cooling by convection – circulating air and accelerating the evaporation of moisture from our immediate surroundings. In contrast, dogs and cats do not have similar types of sweat glands except on the nose and footpads. Their sweat glands produce an oily secretion or film onto the skin but theses glands have no role in heat dissipation. The hair coat acts as an insulator by the creation of a neutral thermal barrier between the outside air and the skin. Spring shedding decrease the density of the hair coat but it still performs a vital insulating function. Hair coat color can affect how much heat will be absorbed though with darker colored hair coats absorbing more heat energy than lighter colored hair coats. Most of the cooling occurs by evaporation of moisture from the respiratory tract (a heat energy transfer process) via panting (so called insensible water loss – loss that is not readily apparent), and by radiating heat from the underbelly areas (armpits, groin and the relatively hairless underbelly). In the extremities, blood that is cooler (in the veins returning blood to the heart) comes in close proximity to blood that is at the core body temperature in the torso (in the blood contained within the arteries); this heat exchange area occurs in the armpit and groin areas. When an animal lays on a cool surface, there is heat exchange between the arterial and venous blood, and between the circulatory system, skin and the cooler floor surface.
An additional factor to consider is the effect that the sun has on the skin, particularly in animals that are groomed, dogs and cats with non-pigmented skin, and in long snouted dogs such as the sight hound breeds or herding breeds such as collies. Vulnerable anatomic locations include the tips of the ears, the end of the muzzle and non-pigmented skin areas; these locations are more prone to sunburn injury. The part of the light spectrum that causes the most skin damage is ultraviolet light. When ultraviolet light comes into contact with certain components of skin such as keratin, melanin (skin pigment), amino acids and the hemoglobin found in red blood cells, energy absorption occurs which can lead to biochemical changes in the skin. These changes can damage virtually any normal skin structure. With sustained injury over time, many changes can occur including overproduction of certain elements within the skin, loss of normal skin structures or mutations within the skin. Melanin absorbs ultraviolet light and helps scavenge “free radicals” (harmful chemical compounds cause by oxidative damage) but melanin also releases free radicals which can also damage the skin. Sun exposure occurs via exposure to direct rays of the sun and also from reflected light from surfaces such as concrete sidewalks or water and sand in beach areas. The ultraviolet exposure that can be damaging typically will occur from 9Am until 3PM; the most intense sunlight during which time sun burning is more likely occurs between 11AM and 2PM. Most solar injuries are related to sunburn effects. A less frequent type of skin injury is photosensitization which s sometimes facilitated by certain medications.
In future posts, we will review strategies to employ to help keep your pet as cool and comfortable as possible during the summertime heat.