Labradors like to eat, and without proper exercise can become obese. Laziness is a contribution to this. Obesity is a serious condition and can be considered the number one nutritional problem with dogs. A study shows that at least 25% of dogs in the United States are overweight. Therefore, Labradors must be properly exercised and stimulated. A healthy Labrador can do swimming wind sprints for two hours, and should keep a very slight hourglass waist and be fit and light, rather than fat or heavy-set. Obesity can exacerbate conditions such as hip dysplasia and joint problems, and can lead to secondary diseases, including diabetes. Osteoarthritis is very common in older, especially overweight, Labradors. A 14-year study covering 48 dogs by food manufacturer Purina showed that Labradors fed to maintain a lean body shape outlived those fed freely by around two years, emphasising the importance of not over-feeding. Labradors should be walked twice a day for at least half an hour.
During the 1880s, the 3rd Earl of Malmesbury, the 6th Duke of Buccleuch and the 12th Earl of Home collaborated to develop and establish the modern Labrador breed. The dogs Buccleuch Avon and Buccleuch Ned, given by Malmesbury to Buccleuch, were mated with female dogs carrying blood from those originally imported by the 5th Duke and the 10th Earl of Home. The offspring are considered to be the ancestors of modern Labradors.
As with some other breeds, the Conformation (typically "Show", "English" or "bench") and the Field (typically "Working" or "American") lines differ, although both lines are bred in both countries. In general, however, Conformation Labradors tend to be bred as medium-sized dogs, shorter and stockier with fuller faces and a slightly calmer nature than their Field counterparts, which are often bred as taller, lighter-framed dogs, with slightly less broad faces and a slightly longer nose. However, Field Labradors should still be proportional and fit within American Kennel Club standards. With Field Labradors, excessively long noses, thin heads, long legs, and lanky frames are not considered standard. These two types are informal and not codified or standardised; no distinction is made by the AKC or other kennel clubs, but the two types come from different breeding lines. Australian stock also exists; though not seen in the West, they are common in Asia. These dogs are also very good with children.