Temperature Adaptation in Northern Dogs

Transcription

1 This article is taken from the March, 1971 issue of "Northern Dog News" although it first appeared in the January, 1971 issue of the Newsletter of the Samoyed Club of Colorado. Temperature Adaptation in Northern Dogs by Ted Greenlee Since we left the Pacific Northwest and moved to Florida with our Samoyeds, I have frequently been asked how they tolerated the heat in this climate. The question usually produced my "five minute lecture" on Northern Dogs in the South. When I repeated this jist of this lecture to Doris and Harold McLaughlin recently, they requested that I write a short paper discussing how Northern dogs adapt to varying temperatures. This discussion actually revolves around at least two scientific works on the ability of arctic animals - seals, whales and Northern dogs among others - to stand exceedingly low temperatures, and on the methods of heat exchange in dogs. I was specifically asked to write this discussion in lay terms "as I spoke them". Since most of my writing activities are related to writing for scientific literature, I find this a very difficult task, but I shall make an attempt. In general, in attempting to discuss work of a scientific nature in lay terms one either talks over the heads of some readers or beneath the knowledge of others and never quite finds the individual who has exactly the right amount of information as you write the article. To begin with, I would like to review a little basic information in relation to temperature control that I am sure most people have been exposed to at some time. The main consideration is that the dog, similar to man, will not tolerate significant variation of his body temperature. Also, most of the reactions taking place in the body, energy producing reactions much like the reactions in an automobile engine, produce heat. Intemperate climates, where the outside temperature is fairly close to body temperature, the primary concern for the animal is to get rid of the excess heat produced. In the case of the automobile, one circulates water through the engine and then passes it through a radiator that has a relatively high degree of efficiency at transferring the heat from the water to, in this case, the air. In general, this is not a terribly efficient method, though it is adequate in the case of the automobile. In the case of man, the radiator, for all practical purposes, is his exposed skin. In order to enhance the loss of heat, man uses the simple principle of evaporation. In general, the amount of heat loss by the evaporation of a certain volume of water from the skin is some five-hundred and

2 forty times greater than the raising of the same amount of water one degree in temperature. This principle of evaporation is very important in many cooling systems and particularly in the cooling of the body. If, however, the major problem ceases to be that of getting rid of excess heat, but rather maintaining what heat is produced in the chemical reactions in the body, one has to look to different techniques. In general, this only becomes necessary if an animal is forced to live in a climate where the temperature is much, much lower than body temperature. This, of course, is the case of the Northern dog. The best way to conserve heat is the well-known method of insulation. The arctic dog's coat is so constructed that it is a very efficient insulator. Therefore, little of the heat produced by the body is lost by means of contact with the outside air through the skin. This, of course, is very good in the winter; but unfortunately, Arctic areas in summer can reach very high temperatures, somewhere in the 70's and 80's or even higher for short periods of time. So, therefore, the animal must also be able to adapt to this increase in temperature. It so happens that the insulation principle is still of use to the animal. If one lives in warmer climates, it is much easier to air-condition a well insulated home than it is to air-condition one that is not insulated. In the case of the animal, the only requirement is that there be some relatively efficient mechanism that the animal can turn on to dissipate his own heat. With a well-insulated body, he will be very little effected by the outside temperature once this mechanism is established. The animal then can maintain his body temperature with changes in outside temperature. Animals that have not adapted this type of mechanism, that is an insulated mechanism, not only will be susceptible to cold, but will also be very susceptible to an abnormal increase in the outside temperature as compared with what he is used to. Therefore, the Northern dog in southern climates will do as well or better in excessive heat that the short-haired dog who is very susceptible to heat stroke. I would now like to discuss two mechanisms of heat control, one which is utilized specifically in the case of Northern animals, and one which is utilized by dogs in general. I would first like to discuss the problems of severe cold and how the animal protects his body temperature in addition to his insulation. It is not possible to totally insulate the dog and in general, the areas not adequately insulated are the areas that are in contact with his snowy world. Those areas are, of course, his feet and legs. Problems of the feet and legs, or in the case of man, the hands and feet, are frequently noted in cold exposure. Man, who is not well insulated, to protect his body temperature and vital organs, will literally shut off blood supply to the feet and hands. When one goes out in the cold and is not properly dressed, one's feet and hands become extremely cold and frostbite or freezing of the fingers and toes is a common occurrence. If this process was followed in the case of a dog in his 60 to 70 degree below zero weather, he would of course be in very bad

3 straits. Therefore, instead of stopping the blood supply to the extremities so the blood does not become chilled, what occurs is that the warm, oxygen carrying arterial blood going into the limb runs right next to the cold, unoxygenated blood leaving the limb. Since they are right next to each other, the warm blood gives up its heat to the cold blood, preventing the loss of this heat as it gets down to the exposed part of the dog's foot. The oxygenated blood can get to the vital parts of the foot to maintain their nutrition, but at the same time does not allow a loss of body heat to the cold air. The ability of the animal's foot and lower leg to live at very low temperatures requires addition adaptation of the tissue, some of which is not well understood. There is one example though that is well understood and noted, and that is the difference in the melting (or freezing, Ed.) temperature of the fat associated with the foot and legs compared to the melting temperature of body fat. The best example of this noted in the case of neatsfoot oil which is the fat from the foot of a cow as compared to the tallow which is the fat from the body of the cow. As you remember, neatsfoot oil is a liquid at normal room temperature, whereas tallow is solid. Therefore, the fat is adapted in the foot of the animal to keep it from becoming solid at these low temperatures and becoming brittle and breaking. I am sure there are other changes in the cells in the tissues of these parts which allow them to tolerate this lower temperature and still function for the animal, but the heat exchange mechanism between the arterial and venous blood in the limbs of cold adapted animals is absolutely essential to their survival. It is possible that a reverse heat exchange takes place in hotter weather. In this instance, blood going to the feet would pick up excess heat in the blood leaving the feet and carry it away from the body, thus preventing a dangerous increase in the animal's body temperature. I doubt, however, if this reverse mechanism plays as important a part in the loss of body heat during hot weather as the heat exchange mechanism does in the protection of the animal in the cold. Now, since the total animal is covered with an insulated coating, perspiring for the loss of heat through the large area of the skin of the body as in man is not practical. Therefore, the animal must have another means of heat loss. Anyone who has dealt with dogs knows that the dog pants when he is hot. It is his panting mechanism that allows the dog to lose heat he does not need when the weather is hot. The mechanism functions on the principle of evaporation. As I have said before, evaporation is extremely effective because you can lose almost five-hundred and forty times as much heat without changing the temperature of the air at all. This evaporation takes

4 place in the dog's nose and is enhanced by the fact that there are many folds of tissue in the nose which increase the surface area that the air is in contact with. In addition, this tissue actually perspires and has a large blood supply, thereby acting much like the radiator in the car. This makes a good mechanism of heat loss, but one needs some way in which to shut it off when one does not want to lose heat. Since the animal must breathe and must take in a pretty constant volume of air at all times, because varying this volume of air would interfere with other bodily functions, people have often been concerned as to how this is controlled. A recent study, just published, has looked into this problem and has come to this conclusion. The air is brought in through the dog's nose and in the case of panting is exhaled through the mouth. In doing this, the air picks up much moisture and heat from the nose, this cooling the nose and drying it. When it is exhaled, it is exhaled through the mouth and since there is much less blood supply to the area around the mouth and the surface area is much less, almost all of the moisture is absorbed and the heat will leave the dog's mouth and be lost. When the dog does not wish to lose body heat, he simply exhales the air that he has brought in through the nose back out the nose, in which case a great proportion of the moisture and heat will be returned to the large surface area and the membranes in the nose thus minimizing the loss of heat. Therefore, when an animal is hot, the hotter the animal is the more of the air he brings in through his nose will be exhaled through the mouth, thus the wide open, tongue out position. If he does not wish to lose heat when it is cold out, he will breathe in and out through his nose and keep his mouth closed. The tongue provides a quite sensitive means of temperature control, particularly in the case of the animal who has other means of protecting himself from the cold and from the outside temperature as do the long-haired Northern breeds. The animal, therefore, in general has developed enough capacity of heat loss through his panting mechanism to compensate for the very wide swings in temperature. In the case of man, the removal of clothing during hot weather increases the ability to lose heat by evaporation of moisture. The dog does not have this ability and therefore his insulation is a protection to him during hot weather. If the animal loses his insulation during very hot weather, by having his coat clipped for instance, he runs the risk of not being able to maintain his body temperature. His skin temperature loss probably is not only inefficient but, since he does not perspire, he will probably increase the temperature of his skin and his body temperature as well. Anything that would interfere with a dog's ability to pant efficiently can also be a great danger to him in hot weather. It is not uncommon to hear of animals who have died of heat stroke after having been given an anesthetic for some minor surgical procedure and then left in a hot car. If

5 the animal is not wide awake or has had an anesthetic, he is not able to compensate for the increased temperature by increased panting. The animal locked in a hot car does not have the ability to open the window as do people and is, of course, very susceptible to heat stroke and death. The dogs in our experience that are most susceptible to hot weather and to sickness from heat are those that have a poor panting mechanism, i.e., the short-nosed dogs such as bulldogs, Pugs, etc. They are extremely susceptible to high temperature and tolerate Southern climates such as ours very poorly unless they are kept in an air-conditioned house. I think the important point to remember in relation to Arctic breed, is that these breeds were able to survive in the Arctic not only because they could tolerate cold but because more precisely, they could tolerate extremely wide swings of temperature in relation to their body temperature. Therefore, they are also, it appears, better adapted for severely high temperatures. The animal that was selected by living in a temperate climate, that is, one in which the temperature stayed very close to the animal's body temperature throughout the year, is not only going to be very susceptible to cold weather, but also is going to be more susceptible to severely hot weather which is well over the dog's body temperature. The final point I'd like to make to in my "Five Minute Lecture" on Northern Dogs in the South is that the Arctic breeds are probably the best heat adaptable dogs one could find, so therefore, I would not be fearful of their presence in a hot climate. However, I might add, there are other problems associated with hot climates such as increase parasites and skin problems that do cause the long-haired Northern dogs to have greater problems than do some of the short-haired breeds.