In the search for disease treatments, the next best thing to human guinea pigs is, well, actual pigs. Believe it or not, their skin and cardiovascular, digestive, urinary and central nervous systems are all very similar to ours. That's why, in recent decades, scientists have established swine models for osteoporosis, heart disease, diabetes, kidney disease and urinary-tract disorders. Mini-pigs, in particular, which weigh about 70 pounds, are easy to examine using hospital scanners and can undergo the same surgical procedures as we do. In fact, most medical students practice on anesthetized pigs before moving on to people. Pigs are also good subjects for behavioral studies such as those necessary for research on Alzheimer's disease, the fatal form of dementia that affects an estimated 4.5 million Americans over the age of 65. It's the sixth leading cause of death in the U.S. and costs the nation $100 billion annually.