Dogs
14
animal-assisted program. Every year, between 6 and 8 million dogs and cats enter US animal shelters. The Humane Society of the United States (HSUS) estimates that approximately 3 to 4 million dogs and cats are euthanized yearly in shelters across the United States. However, the percentage of dogs in US animal shelters that are eventually adopted and removed from the shelters by their new owners has increased since the mid 1990s from around 25% up to around 60-75% in the mid 2000s. Pets entering the shelters are euthanized in countries all over the world because of the lack of financial provisions to take care of these animals. Most shelters complain of not having enough resources to feed the pets and by being constraint to kill them as the likelihood for all of them to find an owner is very small. In poor countries, euthanasia is
usually violent. Domestic dogs have been selectively bred for millennia for various behaviors, sensory capabilities, and physical attributes. Modern dog breeds show more variation in size, appearance, and behavior than any other domestic animal. Nevertheless, their morphology is based on that of their wild ancestors, gray wolves. Dogs are predators and scavengers, and like many other predatory mammals, the dog has powerful muscles, fused wrist bones, a cardiovascular system that supports both sprinting and endurance, and teeth for catching and tearing. Dogs are highly variable in height and weight. The smallest known adult dog was a Yorkshire Terrier, that stood only 6.3 centimetres (2.5 in) at the shoulder, 9.5 cm (3.7 in) in length along the head-and-body, and weighed only 113 grams (4.0 oz). The largest known dog was an English Mastiff which weighed 155.6 kilograms (343 lb) and was 250 cm (98 in) from the snout to the tail. The tallest dog is a Great Dane that stands 106.7 cm (42.0 in) at the shoulder. Like most mammals, dogs are dichromats and have color vision equivalent to red-green color blindness in humans (deuteranopia). The dog's visual system has evolved to aid proficient hunting. While a dog's visual acuity is poor (that of a poodle's has been estimated to translate to a
Biology
Senses