All open or maiden mares residing at the Lazy E Ranch are put under
lights starting December 1. As a result, these mares begin cycling by
mid-February when our breeding season opens. Mares due to foal in January
and February are also housed under lights during this period.
Read below to learn more about the effects of lighting programs on mare reproduction:
The Use of Lights in Mare Reproduction
Heidi Brady, Ph.D.
Assistant Professor of Animal Science
Texas Tech University
As early as the 1940s, it was discovered that the return of the ovulatory season in the mare after the winter could be hastened by the use of an artificial lighting program. These lights were controlled to prematurely simulate days of increased daylength or spring-like conditions. Many studies have since been conducted to define and investigate the mechanisms involved in this process (photostimulation) in the mare. These findings can be applied very practically and fairly inexpensively in most horse breeding operations.
WHAT IS THE OUTCOME OF USING LIGHTS?
The outset of the ovulatory season in mares can be advanced by approximately 40-60 days by maintaining mares under conditions of 16 hours of light (16 light : 8 hours dark) beginning in the fall.
CONTROL OF MARE'S SEASONALITY
The majority of mares, although not all, are classified as Seasonally Polyermous, in that they have a distinct breeding season (late spring and summer) and a period of reproductive inactivity (anestrus). It was important in the evolution of the horse that mares conceive in the summer months (long day breeder) so that, with a 340 day gestation, foals were born under mild conditions.
ROLE OF MELATONIN
During the fall, mares register the decreasing daylength through a gland in the brain called the pineal gland. In response to the increasing periods of darkness, the pineal gland secretes increasing levels of the hormone melatonin. Melatonin acts to supress ovarian activity and cyclicity in the mare, and the mare gradually makes the transition to winter anestrus. The winter ansestrus period is classified by ovarian activity. Ovaries remain small and hard with only very little follicular activity. Ovaries remain small and hard with only very little follicular activity (follicles generally smalled than 15 MM). Ovarian hormones including estrogen and progesterone are minimal and the mares does not cycle.
SPRING TRANSITION PERIOD
As the daylength increases in late winter and early spring, melatonin secretion is decreased and the mare makes the transition from winter anestrus to reproductive cyclicity. Before the mares begin to cycle with regularity, however, they go through a period known as spring transition. The period is characterized by irregular estrous cycles, prolonged heat cycle, split heat periods and other irregularities.
WHY USE LIGHTS?
Because the universal birthdate in the majority of horse breeds is January 1, breeders are pressured to produce early foals. An early foal may have many advantages over a late foal in both sales return and early performance due to size and maturity. The natual or physiological breeding season of the mare, however, occurs late spring and early summer. As a result, we are attempting to breed at a time when the mare is not ready or most fertile. It is more difficult to manage and breed mares during the Transition Period due to cycle irregularities, although regimens of exogenous hormones such as Regu-Mate (Hoechst-Roussel Vet) can be used in breeding at this time.
By placing mares under lights, this transition period will occur earlier and thus the more regular cycles will also occur earlier. It should be noted, however, that the use of a lighting program will not shorten the transition period, only advance the occurrence of this period.
The required amount of light to hastem the onset of the breeding season is a minimum intensity of 10 foot-candles or 1018 lux. Practically, a 200 watt incandescent bulb is sufficient for a normal sized horse stall. Both incandescent or fluorescent lighting are effective.
The amount of light can be checked by the use of the light meter in a single lens reflex camera. Briefly, this method involves setting the ASA at 400, the shutter speed at 1/4s and using a styrofoam cup over the lens as a diffuser. Aperture settings of f4 and above represent adequate light (10 foot-candles.
A lighting program can also be implemented in an outdoor situation. Mares in a dry lot or paddock can be placed under large lights on poles. Care should be taken, however, that there are no dark corners or tall feeders which may shield certain mares from light.
In many breeding operations, a lighting program is implemented with the use of timers. Timers can be set so that the lights come on at 4:30 or 5:00 in the afternoon and remain on until 10:30 or 11:00 p.m. This places the mare in conditions of 16 hours of light and 8 hours of dark. Adjustments should be made with the timing of sunrise and sunsets to ensure this. The prices of timers are very reasonable, starting at $20 for the most simple devices.
Other breeding operations with regimented schedules utilize the personnel to operate the lights. For example, lights are manually turned on during or after feeding at approximately 5:00 p.m. and the night watchman will turn them off at 11:00 p.m. It is critical that the lighting schedules are adhered to strictly for effective results.
WHEN DOES THE LIGHTING PROGRAM NEED TO START AND FINISH?
The mares should be placed under lights by December 1 to have a significant effect in the Spring. May breeding farms use Thanksgiving holidays as a starting date for the initiation of the lighting program. The lighting program should be continued in the Spring until the natural lighting meets the requirments.