Researchers know that exposing stabled mares to an artificially extended day using a 100 Watt light bulb starting Dec. 1 can advance the breeding season by as much as three months. | Photo: Courtesy Equilume

Light—naturally derived from the sun—drives the internal clocks of all organisms on earth. Those clocks regulate all aspects of physiology and give rise to circadian (24-hour) rhythms in almost all of our behavioral, physical, and biochemical processes. Physical activity, body temperature, heart rate, blood pressure, hormone levels, sleepiness, and more all undergo rhythmic undulations over the 24-hour period in response external cues, including light.

“The light-dark cycle in a 24-hour period is one of the most important environmental cues, referred to as ‘zeitgebers,’ that synchronize an animal’s internal clock to the earth’s 24-hour rotation,” said Barbara Murphy, BScEq, PhD, of the University College Dublin School of Agriculture and Food Science in Ireland. Murphy has been studying chronobiology (the science of biological time-keeping) in horses for the past 15 years.

“Synchronization between an animal’s daily rhythms and their environment helps ensure optimum survival by allowing them to anticipate activity, feed availability, and predation pressure,” she added