Results show that by adding supplemental lighting to lactating dairy cows to achieve 16 to 18 hours of light per day increased milk production from 5 to 16 percent in research herds. T he pineal gland in most mammals is controlled by the amount of light seen through the eyes each day. This pineal secretion includes the substance melatonin. Increased amounts of light exposure actually decrease the amount of melatonin synthesis and release from the pineal gland. In all species studied melatonin has been found to reach peak concentrations in darkness in cerebral spinal fluid, blood, and urine.
Turkey has high levels of the amino acid tryptophan.
Tryptophan is actually a major precursor of melatonin. Again, higher levels of melatonin produced naturally by your system cause this affect. In most northern climates the natural day length is less than 13.5 hours during the fall, winter and spring months. M any producers already have adequate lighting in their barns, they just fail to leave those lights on for a long enough duration during the fall, winter and spring months. To measure this, a simple light or lumen meter can be used in the barn.