Now, researchers at the University of Wisconsin-Madison have discovered they can boost calcium levels in milk by giving cows regular injections of the hormone serotonin, a chemical messenger that among other things is linked to feelings of happiness. If you think the life of a modern milk cow is already pretty happy—lounging in green fields under clear blue skies—think again. With the rise of factory farming, most overseas cows don’t get to see a lot of green pastures.