The thoroughbred industry, as you may know, has classifications for horses that are hundreds of years old. One of the classifications refers to the age of a horse and defines acceptable activities for that horse. A 'yearling' defines a horse between one and two years old; however, horses born in the second half of one year are considered yearlings on January 1 of the next year, even though they are not between one and two years old, and not physically ready to participate in equivalent activities.
Perhaps the industry would consider counting months since birth, instead of just years... but, instead, breeders have been putting mares 'under the lights' in their barns to try to control their mating periods.
Exposing mares to more light at night postpones the activity of the hormone melatonin, so the horses have 'longer days.' As melatonin influences other hormones that ready the mare for mating, those won't be stimulated either until the 'days' get shorter. The objective of these activities is for newborn thoroughbreds to be born as close to January 1 as possible.
The Equilume light mask eliminates the need for overhead
lighting to control a mare's birthing cycle, but it also can be used to reduce
gestation periods in mares (the average gestation is around 11 months), treat
jet lag in horses, and encourage hair shedding earlier in preparation for show
circuits. It does all this by providing a low level of light into one
eye.
sources: Irish Times, Wikipedia
