Body Clock: An organism’s natural internal timing system, a biological mechanism which causes your body to automatically behave in particular ways at particular times of the day. It functions to keep the body’s activities synchronised with the external environment. The body clock is affected by a number of external factors, primarily light, but also feeding and exercise.
Circadian Rhythm: From the Latin words “circa”, meaning about, and “dies”, meaning day, circadian rhythms are physical, mental and behavioural changes that follow an approximate 24-hour cycle and ensure the body clock stays in tune with the daily light/dark cycles. These rhythms function to coordinate internal physiology and behaviour with the external environment to support health, behaviour and wellbeing. Examples of circadian rhythms include sleep/wake patterns, eating habits, alertness, performance, heart rate, body temperature and blood pressure.
Melatonin is the hormone associated with darkness and its levels rise at night. Long nights during the winter months result in long durations of high melatonin production shutting down the mare’s reproductive system. Suppressing the rise of melatonin via natural or artificial light lengthens the day and triggers the start of the mare’s reproductive cycle in the spring.
Blue–enriched light: Light that contains a high proportion of short wavelength light from the blue end of the spectrum and best replicates natural daylight. This light does not appear blue to our eyes, but may look cooler. Blue-enriched light contains light wavelengths from 460–490 nanometres which optimally stimulate specialised receptors in the retina that are responsible for signalling the time of day to the brain, and from there to the rest of the body. Blue-enriched light optimally suppresses melatonin during daytime in horses.