Using Artificial Light for Mares

With the shortest day of the year right around the corner, it's easy to see why bears choose to hibernate!  But did you know that mares have their own, much less intense, version of hibernation called anestrus? 

Anestrus is defined as a 'reproductive quiescence', or basically a period where mares will not come into heat for breeding.  Control of the mare's, and many other species, reproductive rhythm stems from the photoperiod - the part of the retina that perceives daylight.  As the days shorten, the photoperiod relays this information to the brain, specifically the pineal gland, which then begins to secrete increasing levels of the hormone melatonin.  While melatonin is often dubbed the 'sleep hormone', it also suppresses the mare's reproductive activity. 

Since foals born early in the year have the tendency to outperform those born later - especially in the racehorse industry - manipulating the mare's natural breeding cycle can be advantageous.  The most common and reliable method is through the use of artificial lights to alter the mare's perception of day length.  The easiest light management program is to use lights at the end of the day to extend the perceived day length to 16 hours at the start of December (to induce heat between February-March).  This practice entails turning on an artificial light source 30 minutes before sundown.  Perception of day length must be constant from day to day, so the use of automatic timers is beneficial.  It should also be noted, that mares exposed to too much light will not cycle at all.

Light intensity should be a minimum of 2-foot candles, which is comparable to one 200-watt bulb for a 12x12 foot stall, with no dark corners for the mare to stand in.  A good rule of thumb is to light the enclosure enough to where you can read the fine print on a newspaper in the darkest corner of the stall.

Artificial lighting programs work best in stalls; however, floodlights have can be used in outdoor pens and paddocks to create a similar effect.  Keep in mind though, mares that undergo an artificial light program will also shed their hair, so mares housed outside will need protection from bad weather. 

While the use of artificial lights has the greatest benefit on dry or open mares, recent studies have shown that early foaling mares will also respond to added light.  Gestation lengths have been decreased by as much as 10 days when using lights for open mares, with no effect on foal weight and size.  Artificial light programs also stimulates mares to properly cycle after foaling as well.