Artificial Light and Hair Growth in Horses

Horses exposed to cold weather grow longer, thicker coats to help maintain their core body temperatures. Despite being a necessary adaptation for many horses, some owners find thicker coats bothersome, especially when horses are ridden daily. Performance horses are often body-clipped and appropriately blanketed in order to dissipate heat and dry more quickly.

As an alternative to body-clipping, one group of researchers recently examined the use of artificial lights to alter coat growth in horses.

“Traditionally, the use of artificial lights in the winter advances the breeding season, allowing mares to be bred earlier in the calendar year,” relayed Catherine Whitehouse, M.S., a Kentucky Equine Research nutrition advisor.

In a recent study, researchers found that high melatonin levels that coincide with short daylight hours suppress prolactin. In turn, prolactin plays a role in many body systems, including hair growth.^* Specifically, prolactin receptors found in hair follicles control whether hair grows, sheds, or enters a state of quiescence.

“Thus, by increasing the number of hours a horse is exposed to daylight, melatonin levels can theoretically be suppressed, as we see in breeding programs, and the development of a thick winter coat can be avoided,” explained Whitehouse.

A series of experiments was conducted using wearable blue light masks that covered one eye and provided 15 hours of light per day. The researchers found:

• When the photoperiod was extended within one month of the summer solstice, the summer coat was maintained in stabled horses;
• Extending the photoperiod beginning with the autumnal equinox did not reverse winter coat growth; and
• Initiating artificial lighting one month prior to the winter solstice accelerated shedding in outdoor-living horses. No accelerated shedding was noted if artificial lighting began one month after the winter solstice.

While photoperiod certainly appears to play an important role in coat growth, temperature, breed, and management factors (stabling, feeding, blanketing, grooming) also modulate coat growth in horses.

“In terms of nutrition, offering nutritional supplements that support coat quality, such as BioBloom PS. This palatable product provides essential amino acids and fatty acids derived from full-fat soybean to promote healthy coat and skin,” Whitehouse added.  Look for Bio-Bloom HF in Australia.

*O’Brien, C., M.R. Darcy-Dunne, and B.A. Murphy. 2020. The effects of extended photoperiod and warmth on hair growth in ponies and horses at different times of year. PLoS One 15(1):e0227115.