Broodmare owners who want to breed their mares before the horse's natural breeding season (April to October in Alabama) and show horse owners who want their horse's haircoat short and shiny for shows early in the year can use an extended photoperiod to accomplish these goals. Extending the natural photoperiod (daylight hours) with artificial lighting can "trick" the horse's body into believing it is spring. Most horses will begin to shed their winter haircoat after 30 to 60 days on an extended photoperiod and most open broodmares will begin to show signs of heat and ovulate after 60 to 90 days.

To extend the photoperiod of horses, owners should put broodmares and show horses under lights during mid November/early December and keep them under lights throughout the winter. The majority of horses exposed to this program will shed their winter coat by February, and broodmares should have a fertile heat cycle before March. Lights in the horse's stall or in a outdoor holding pen should be turned on from approximately 5:00 p.m to 10:00 p.m. daily. This gives the horse a total photoperiod of 15 to 16 hours of light which is the same amount the horse would receive from daylight during the summer. Leaving lights on continuously at night is not as effective as a 16 hour daylength so a light timer is useful in a lighting program. Two footcandles of light provide enough illumination for an artificial lighting program. In a 10 by 10 foot stall, one 200 watt incandescent bulb or two 40 watt florescent bulbs will provide enough light. A general rule is to provide enough illumination to easily read a newspaper in the most dimly lit area of the pen or stall.

Horse owners should remember that horses under an extended photoperiod have little protection against cold weather because they will shed their winter coats. To help these horses stay warm (especially broodmares kept outside), owners should make sure horses have windbreaks, shelters where they can stay dry, and plenty of hay or pasture to help them generate body heat. Under severe cold weather conditions, horses may have to be blanketed to help them maintain their body heat.

Broodmares foaling early in the year (January through March) may enter their normal winter anestrus (the time when they are not having heat cycles) after foaling. If early rebreeding is desired, these mares should be kept under lights through foaling and rebreeding.