There is disclosed a light-based method of causing a substantial suppression of melatonin production, the method comprising the step of shining blue light from an artificial blue light source into just one eye of a bovine, causing a substantial suppression of melatonin production in the bovine, sufficient to induce physiological change. There is further disclosed a device for causing a substantial suppression of melatonin production, the device comprising a headpiece fittable to a bovine's head, and including an artificial blue light source, the headpiece operable to shine blue light from the artificial blue light source into an eye of the bovine, causing a substantial suppression of melatonin production in the bovine, sufficient to induce physiological change.
