It has long been a goal for equine breeders to produce foals born as early in the year as possible. Foals born early in the year have a distinct economic advantage for breeders. However, Mother Nature, has a different plan.
Mares are seasonally polyestrous long day breeders. They cycle regularly from late spring until early fall when the day length is the longest. It is estimated that 75-85% of mares become anestrous during the winter months. During this time their cycles can range from nonexistent to very erratic cycles with or without ovulation. At the end of the winter anestrous period mares will go through a “transition” period. This transition period is also marked by irregular and erratic estrous behavior and multiple small follicles developing without true ovulation and corpus luteum formation. The transition period is said to be complete when a dominant follicle develops, ovulation occurs, and a corpus luteum is formed. Normal cycling should then commence. However, this could occur as late as mid-May or June without the use of artificial lights
Breeders have traditionally used phototrophic stimulation to hasten the onset of normal cyclicity to aid in artificially adjusting or moving the transition period as early in the year as possible. Changes in day length are the primary regulator of cyclicity in mares. Melatonin is produced in hours of darkness and its production is decreased as day length increases in the spring. Mares can be stimulated to perceive that spring is coming sooner by exposing them to extended periods of artificial light. It should be noted, that stimulating mares with increased exposure to light should be preceded by a period of short day length in the fall months. Mares in show training that are kept under an artificial light program year round and constantly receiving phototrophic stimulation could potentially choose a period to go anestrous at an inappropriate time, like March or April, for example.
Several phototrophic stimulation protocols have been successfully used for many years. One can provide a period of 14-16 hours of light per day starting approximately 60 days prior to the time of expected breeding. It is generally accepted that the light should be added at the end of the day. For example, if a mare owner would like to breed a mare in the early part of February, the mare should be exposed to artificial light extending the natural day length to 14-16 hours starting December 1. Two additional plans have been used successfully that are more cost effective but require a bit more management and planning. The first protocol adds 2-2 ½ hours of artificial light immediately following sunset and the other protocol involves a 1-2 hour pulse of light starting 9 hours after sunset.
Enough light should be provided that one could comfortably read a newspaper or magazine anywhere in the stall. One must also consider that the mare will not be stimulated if there is sufficient light in her stall but she has access to an outdoor run where she can go stand in the dark. So, mares need to be confined to the stall.
It is very important that a lighting program be very well managed. It has been shown that even a three day interruption in the lighting program can interfere with phototrophic stimulation.
Pregnant mares expected to foal early in the season that are to be rebred should also be put under lights just as barren mares. Mares due to foal prior to March 1 should follow the same protocol, as many mares will slip into anestrous after foaling if they foal early in the year.
Recently, new technology has been developed to address some of the more cumbersome aspects of a phototrophic stimulation program. Low intensity blue light of the correct wavelength has been shown to stimulate receptors in the eye that are responsible for inhibition of melatonin production. Also, it is only necessary to stimulate one eye. Hence, Equilume Light Mask was developed. It is a mask that provides low level blue light to a single eye. It is battery powered and is on an automatic timer. Once activated the blue light will turn on when natural light levels drops at dusk. The light will remain activated for 7 hours, turn off, and start again the next evening. The battery is designed to last for an entire breeding season.
A research study was performed to determine the effectiveness of these masks at advancing the breeding season in mares. B.A. Murphy et al collected data on three different groups of mares. In group 1 the mares were housed indoors under lights. The group 2 mares were housed outside and wore the light masks which were programmed to be on from 4:30 pm until 11:00 pm. The Group 3 mares were housed outside without any artificial light in order to serve as the control group. Researchers concluded there was no difference between the number of cycling mares whether they were housed in a barn under lights or if they were maintained outside while wearing the blue light masks.
This new technology could provide flexibility for breeders. Since mares could be kept outside instead of remaining in a stall the mare owner can save money associated with bedding, electricity and labor. As an added bonus, mares which may have behavioral problems associated with being in a stall could remain outdoors.