Ask Your Veterinarian Presented By Kentucky Performance Products: Putting Broodmares Under Lights by Paulick Report Staff|02.17.2022|4:10pm Veterinarians at Rood and Riddle Equine Hospital answer your questions about sales and healthcare of Thoroughbred auction yearlings, weanlings, 2-year-olds and breeding stock. Question: When it comes to putting broodmares under lights for cycling are overhead lights or mask lights better? And why does it work? Dr. Peter Sheerin, Rood and Riddle Equine Hospital: In many breeds, Jan. 1 is considered the birthdate for all horses in the breed, no matter when they are born. This can put late-born foals at a disadvantage when competing or at yearling sales. Because of this, many breeders want their mares to foal as early as possible. The horse is considered a long day breeder, meaning they are cycling when the days are longer. Mares left at natural conditions in the Northern Hemisphere will typically start cycling late March to early April. Mares further north will start cycling later than mares closer to the equator. Researchers determined that by artificially increasing the day length and the amount of light that mares were exposed to, one could get mares to cycle earlier. Mares did not begin to cycle for 60 to 75 days after the beginning of exposure to longer days. So, for a breeding season that starts Feb. 15, one would start lights Dec. 1 at the latest. They also determined that light alone was not the only factor that influenced when the mares would begin cycling. Temperature and body condition also played a role. Mares in colder environments began cycling later than mares in warmer environments. Thin mares began cycling later than mares in good body condition. It was also discovered that mares needed 14.5 to 16 hours of daylight to respond to the light therapy and that the light must be added in the evening. Using this information, it was suggested mares be kept under lights in a barn until approximately 11 p.m. There are some variations to this regime that can be used, but they require more effort with respect to gradually adjusting the start exposure to correspond with sunset or a shorter period of light nine hours after the onset of darkness. Dr. Pete Sheerin With that background, we get to your question: Which is better, overhead lights or light masks? The answer is it depends. With overhead lights, the mares are in stalls or in a catch pen for an extended period. You can turn them out when the lights go off, but there is increased labor involved with turnout, cleaning stalls, more hay and straw used, cost of disposal of extra dirty bedding, and higher electric bills, among other things. If mares are in a catch pen outside under lights some considerations include: do you have enough lights that they are exposed to sufficient intensity of light for the entire time and are the temperatures extreme enough to influence when they start cycling. The light masks (Equilume®) have an initial cost to purchase and then an annual cost to replace the light source. There is also the issue of weather conditions that need to be considered. Both systems work well. You will just need to put pencil to paper to determine which works best for you. A few considerations include: how many mares you want to start cycling early, what your facilities are like, what your labor costs are, and what your weather conditions are like. Dr. Sheerin was born and raised in New York City. His first experience with horses was soon after his family moved to Lagrangeville, a small town north of the city. He began working on a Thoroughbred breeding farm where he gained experience in all aspects of the Thoroughbred industry. During high school, he also competed on the varsity crew team, and his love of rowing took him to Syracuse University where he majored in biology. Following graduation, Dr. Sheerin moved to Florida to manage a small Thoroughbred breeding farm in Ocala. Several years later, he began graduate research in equine reproductive physiology at the University of Florida under mentor Dr. Dan Sharp while managing the endocrinology lab at the University of Florida College of Veterinary Medicine. Dr. Sheerin then entered veterinary school, where he expanded his interest in theriogenology, particularly large animal theriogenology. Dr. Sheerin became board certified in theriogenology in 2001 upon completion of his residency at the University of Florida.. He is a member of the American Association of Equine Practitioners, the American Veterinary Medical Association, and the Society for Theriogenology. Dr. Sheerin has lectured both nationally and internationally on the reproductive aspects of the mare and stallion. Dr. Sheerin and his wife Barb have three daughters.