Near the Danish city of Ikast, some 1,500 spectators gathered on April 19 to celebrate what has become something of a national holiday at organic dairy farms around Denmark. Courtesy of Organic Denmark hide caption

itoggle caption Courtesy of Organic Denmark

Cows rotate in the milking parlor at Fair Oaks Farms, a large-scale dairy and tourist attraction, near Rensselaer, Ind. Dan Charles/NPR hide caption

itoggle caption Dan Charles/NPR

The milk's industry's new campaign, Milk Life, features ordinary people accomplishing all sorts of tasks after jumpstarting their day with a glass of milk. Courtesy of Milk Processor Education Program hide caption

itoggle caption Courtesy of Milk Processor Education Program

A customer shops for milk at a Safeway in Livermore, Calif. Although it may seem counterintuitive, there's growing evidence that full-fat dairy is linked to reduced body weight. Justin Sullivan/Getty Images hide caption

itoggle caption Justin Sullivan/Getty Images

A new study on lactose tolerance among early farmers in Spain challenges a leading theory that humans developed an appetite for milk to avoid calcium deficiency. iStock hide caption

itoggle caption iStock

Sticker shock in the dairy aisle? If the government fails to pass the farm bill, milk prices could spike sometime after the first of the year. George Frey/Landov hide caption

itoggle caption George Frey/Landov

Madison Fitzgerald, 20, holds her baby, Jake, in the neonatal intensive care unit at Texas Children's Hospital in Houston. Jake, who was born 16 weeks too early, receives donor breast milk every three hours by mouth. Carrie Feibel/KUHF hide caption

itoggle caption Carrie Feibel/KUHF
Katherine Streeter for NPR

Researchers are learning more about how to treat milk allergy by giving kids a small amount of milk protein, but it needs further study. MICHAEL PROBST/ASSOCIATED PRESS hide caption

itoggle caption MICHAEL PROBST/ASSOCIATED PRESS

Parents are currently advised to switch toddlers to reduced-fat milk at age 2. David M. Goehring/Via Flickr hide caption

itoggle caption David M. Goehring/Via Flickr

Thousands of years ago, a mutation in the human genome allowed many adults to digest lactose and drink milk. iStockphoto.com hide caption

itoggle caption iStockphoto.com

Dairy farmer Bob Andrews feeds heifers in the same barn his grandfather used. He says today "the harder you work, the further you get behind." David Sommerstein/NCPR hide caption

itoggle caption David Sommerstein/NCPR