For those involved in breeding and performance horse industries, timing is everything. Mares are long-day breeders, meaning their reproductive cycles are dictated by the amount of daylight they receive. This often leads to a gap in fertility during the winter months, with mares not coming into heat until mid-spring. However, in todays competitive age of futurities, there’s a demand for foals to be born earlier in the year, closer to January 1st the better. The most common and effective way to do this is by using artificial lighting—referred to as "putting a mare under lights."
What is Artificial Lighting and How Does it Work?
The goal of using artificial lighting is to simulate the longer days of spring, tricking the mare’s body into thinking the seasons are changing sooner than they actually are. Horses naturally cycle in response to the length of the day. When days are short, as they are in winter, mares go into a state called "anestrus" where they do not cycle or “shut down”. By extending the amount of light they receive, we can advance their mare’s reproductive cycle, encouraging her to enter her transition period earlier and begin cycling in late winter or early spring, rather than waiting until mid-spring.
When Should You Begin the Lighting Protocol?
To optimize this process, lighting should begin as close to December 1st as possible. This is when the timing becomes crucial. Studies have shown that the most effective schedule involves turning on the lights slightly before sunset and turning them off by 11 p.m. This results in a total of 16 to 18 hours of light exposure per day, combining both natural and artificial light.
The lighting protocol typically takes around 60 to 70 days to stimulate the mare’s reproductive system, meaning you should start by early December if you want her to start cycling in February or March.
What Are the Specific Lighting Requirements?
Vaughn Cook always said, “If you can read a news paper in the darkest corner of the stall, then that’s the perfect amount of light.” For the lighting to be effective, a few key factors must be considered:
Light intensity: A light intensity of at least 10-foot candles (about 100 lux) is required, which is typically achieved with 100 to 200-watt incandescent or fluorescent bulbs.
Duration: The artificial light should be on for a total of 16 hours per day, starting just before dusk and ending by 11 p.m. That being said, mares also need darkness and should not be put under lights 24/7 that is why some mares do not cycle correctly when they have been put under yard lights that do not shut off.
Consistency: It’s crucial that the lights turn on at the same time every evening to maintain a consistent light schedule. Using timers is highly recommended to avoid human error.
Can Pregnant Mares Be Put Under Lights?
While the protocol is most often used for mares that are not pregnant but are being prepared for breeding, there are cases where pregnant mares may also benefit from artificial lighting. This is particularly true for mares due to foal in January, February, or early March. If the goal is to breed the mare back quickly after foaling.
It’s important to note that housing pregnant mares under lights is not necessary for those due to foal later in the spring, as they are less likely to experience post-partum anestrus.
Why Should You Put Your Mares Under Lights?
Artificial lighting is a reliable, non-invasive way to manipulate a mare’s reproductive cycle. Compared to hormone injections or other treatments, the lighting protocol is often less expensive and more straightforward, with proven success. By starting early (ideally by December 1st), you can ensure that your mare is ready for breeding in early spring, leading to foals that are born earlier in the year. This gives your foals a competitive advantage in racing and performance disciplines, where age at the time of yearling sales or futurities can be critical.
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