Dogs go through four stages of the life cycle: puppy, adolescent, adult and senior. Like humans and other mammals, individual dogs move through the stages of the life cycle at different rates. The rate of aging depends on factors such as genetics, nutrition and the quality of care your dog receives.
The puppy stage of the life cycle begins after about 63 days of gestation. This stage lasts until the dog is 6 to 18 months old. For at least the first 8 weeks of his life, your puppy should be with his mother and siblings. During the puppy stage -- both while with his mom and after he comes to you -- your dog is learning about the proper way to interact with humans, other dogs and other pets sharing his home. During this stage of the life cycle, it's important to begin house training and get your puppy's compete set of vaccinations.
The puppy stage will give way to adolescence sometime between the ages of 6 and 18 months. Smaller breed dogs will go into the adolescent stage earlier than larger breed dogs. This is the stage of the life cycle when hormones start to kick in and, if not spayed/neutered, your dog may begin to act like a moody teenager. Your dog will lose his puppy fur and grow to his adult size, though he may be awkward with his body and appear gawky until he gets accustomed to his new size. At the beginning of this stage of the life cycle have your dog altered and consider obedience training.
Between the ages of 1 and 3 years, your dog enters the adult stage of life. As with adolescence, smaller breeds reach this stage in less time than larger breeds. During this phase of the life cycle, your dog will still enjoy plenty of exercise and playtime, but he likely won't be so demanding of your attention and will not burst with the same amounts of energy that kept you busy during earlier stages. He is likely completely house-trained by now. Consider obedience training or advanced training. Your adult dog will continue to thrive from the mental and physical exercise of learning.
From adulthood your dog will enter the senior stage of the life cycle sometime between his 6th and 10th birthday. Unlike with adolescence and adulthood, larger breed dogs reach this stage of the life cycle at a younger age than smaller breed dogs. During this stage of the life cycle your dog's muzzle will likely begin to gray. He will move more slowly and, instead of a brisk game of fetch, he'll be more content with a stroll. Your senior dog may eat less and sleep more than he has at other times of his life.
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