Dogs
What is a Dog?
The dog is a type of canid, a mammal in the order Carnivora. The term includes both wild (feral) and domestic variants, but commonly excludes other canids such as wolves.
Over time, the dog has developed into hundreds of breeds with a great degree of variation. For example, heights at the withers range from just a few inches (such as the Chihuahua) to roughly three feet (such as the Irish Wolfhound); colors vary from white through grays (usually called blue) to black, and browns from light (tan) to dark (”red” or “chocolate”) in a tremendous variation of patterns; and coats can be anything from very short to several centimeters long, from coarse hair to something akin to wool, straight or curly.
Physical characteristics Of Dogs
Modern dog breeds show more variation in size, appearance, and behavior than any other domestic animal. Within the range of extremes, dogs generally share attributes with their wild ancestors, the wolves. Dogs are predators and scavengers, possessing sharp teeth and strong jaws for attacking, holding, and tearing their food. Although selective breeding has changed the appearance of many breeds, all dogs retain basic traits from their distant ancestors. Like many other predatory mammals, the dog has powerful muscles, fused wristbones, a cardiovascular system that supports both sprinting and endurance, and teeth for catching and tearing. Compared to the bone structure of the human foot, dogs technically walk on their toes.
Dogs Sight
Dogs were thought to be dichromats and thus, by human standards, color blind.[8][9] It is now known that dogs can’t see the colour red very well.
Different breeds of dogs have different eye shapes and dimensions, and they also have different retina configurations.[10] Dogs with long noses have a “visual streak” which runs across the width of the retina and gives them a very wide field of excellent vision, while those with short noses have an “area centralis” — a central patch with up to three times the density of nerve endings as the visual streak — giving them detailed sight much more like a human’s.
Some breeds, particularly the best sighthounds, have a field of vision up to 270° (compared to 180° for humans), although broad-headed breeds with short noses have a much narrower field of vision, as low as 180°
Dogs Hearing Capabilities
Dogs detect sounds as low as the 16 to 20Hz frequency range (compared to 20 to 70 Hz for humans) and above 45 kHz[11] (compared to 13 to 20 kHz for humans)[9], and in addition have a degree of ear mobility that helps them to rapidly pinpoint the exact location of a sound. Eighteen or more muscles can tilt, rotate and raise or lower a dog’s ear. Additionally, a dog can identify a sound’s location much faster than a human can, as well as hear sounds up to four times the distance that humans are able to. Those with more natural ear shapes, like those of wild canids like the fox, generally hear better than those with the floppier ears of many domesticated species.
Dogs Smelling Power
Dogs have nearly 220 million smell-sensitive cells over an area about the size of a pocket handkerchief (compared to 5 million over an area the size of a postage stamp for humans). Some breeds have been selectively bred for excellence in detecting scents, even compared to their canine brethren. What information a dog actually detects when he is scenting is not perfectly understood; although once a matter of debate, it now seems to be well established that dogs can distinguish two different types of scents when trailing, an air scent from some person or thing that has recently passed by, as well as a ground scent that remains detectable for a much longer period. The characteristics and behavior of these two types of scent trail would seem, after some thought, to be quite different, the air scent being intermittent but perhaps less obscured by competing scents, whereas the ground scent would be relatively permanent with respect to careful and repetitive search by the dog, but would seem to be much more contaminated with other scents. In any event, it is established by those who train tracking dogs that it is impossible to teach the dog how to track any better than it does naturally; the object instead is to motivate it properly, and teach it to maintain focus on a single track and ignore any others that might otherwise seem of greater interest to an untrained dog. An intensive search for a scent, for instance searching a ship for contraband, can actually be very fatiguing for a dog, and the dog must be motivated to continue this hard work for a long period of time.
Dogs Diet
At present, there is some debate as to whether domestic dogs should be classified as omnivores or carnivores, by diet. The classification in the Order Carnivora does not necessarily mean that a dog’s diet must be restricted to meat; unlike an obligate carnivore, such as the cat family with its shorter small intestine, a dog is dependent on neither meat-specific protein nor a very high level of protein in order to fulfill its basic dietary requirements. Dogs are able to healthily digest a variety of foods including vegetables and grains, and in fact can consume a large proportion of these in their diet. Wild canines not only eat available plants to obtain essential amino acids, but also obtain nutrients from vegetable matter from the stomach and intestinal contents of their herbivorous prey, which they usually consume. Domestic dogs can survive healthily on a reasonable and carefully designed vegetarian diet, particularly if eggs and milk products are included. Some sources suggest that a dog fed on a strict vegetarian diet may develop dilated cardiomyopathy since it lacks L-carnitine, [12] however, maintaining a balanced diet is also a factor since L-carnitine is found naturally in many nuts, seeds, beans, vegetables, fruits and whole grains. In the wild, dogs can survive on a vegetarian diet when animal prey is not available. However it has been noted, both by observation of extremely stressful conditions such as the Iditarod race and by scientific studies of similar conditions, that high-protein (approximately 40%) diets including meat help prevent damage to muscle tissue. (This research is also true for some other mammals.) This level of protein corresponds to the percentage of protein found in the wild dog’s diet when prey is abundant; higher levels of protein seem to confer no added benefit.
Dogs frequently avidly eat grass, which is a harmless activity. Explanations abound, but rationales such as that it neutralizes acid, or that eating grass might make the dog vomit, so dogs eat grass to remove unwanted substances from their stomachs, are at best educated guesses. Dogs do vomit more readily than humans, as part of their typical feeding behavior of gulping down food then regurgitating indigestible bones, fur, etc. This behavior is typical of pack feeding in the wild, where the most important thing is to get as much of the kill as possible before others consume it all. Individual domestic dogs, however, may be very “picky” eaters, in the absence of this evolutionary pressure.
Source: Dogs
