The Science of Shedding

To better understand how to help your horse shed, it’s useful to know the science behind shedding. The first and most important factor that determines equine coat length is photoperiod, or the length of sunlight hours during each day. According to a 2020 equine shedding study  from the School of Agriculture and Food Science, University College of Dublin, Ireland, after entering the retina, “seasonally changing environmental light information (24-hour light/dark cycles) is transmitted via the retino-hypothalamic tract to the bilaterally paired suprachiasmatic nucleus (SCN) in the hypothalamus.”

In turn, “the SCN, also referred to as the ‘master clock’ or ‘pacemaker’ of the body, encodes these ‘time-of-day’ signals and disseminates them throughout the organism… At the pineal gland, the SCN signal affects melatonin secretion such that daylength duration is inversely proportional to duration of melatonin production, highlighting its central role in regulating mammalian physiological responses to photoperiod.” Less melatonin means less hair growth, so melatonin production falls off in the spring when the days are longer.

There is some early-stages scientific evidence supporting the inducement of shedding by exposing horses to short-wavelength blue light in the spring and fall. However, leaving the lights on in your horse’s stall likely will not be enough; special blue-light masks are required for full effectiveness. The study also found that the masks were much more effective for preventing hair growth in the fall than they were for stopping hair growth in the spring.

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