Pet strollers offer one way for pet owners to get around with dogs, cats and other pets that are sick or elderly.

But strollers aren't just for infirm or elderly pets. Some are for perfectly mobile pets who are more child than pooch. Because dogs can be zipped securely into their strollers, the strollers allow pets to accompany owners on an entire day’s worth of activities.

In 2001, US pet owners spent $7.1 billion on pet health care, a number that jumped to $13.41 billion in 2011, according to the American Pet Products Association. Along with that spending has come an increase in the percentage of senior pets who, having benefited from life-prolonging therapies, need help getting around. In 1987, forty-two percent of dogs were 6 years old or older, according to the American Veterinary Medical Association. In 2011, that number had risen to 48 percent. The percentage of senior cats is growing at an even faster rate. In 1987, 29 percent of cats were 6 years old or older. By 2011, 50 percent of cats were “of a certain age.”