Blue light therapy may relieve PPID-equine equine coat problems

Researchers report in a new study that exposing horses with pituitary gland dysfunction (PPID, formerly known as equine Cushing’s disease) to a few hours of blue light every day for part of the year can make them grow lighter and shorter winter coats.
While blue light therapy does not affect adrenocorticotropic hormone (ACTH) levels, it may reduce hair growth — possibly by simulating long summer days, said Barbara Murphy, PhD, assistant professor in the College of Agriculture and Food Sciences at University College Dublin. in Ireland.

The findings do not offer a cure for the disease itself, Murphy said, but offer a way to improve well-being by making PPID-positive horses more comfortable. “If there is any way we can relieve one of the main symptoms [of PPID]Let’s do it!” she said.

Murphy explained that horses with PPID have larger than normal increases in ACTH in the fall, and their winter coats often grow in heavier and thicker than other horses. This excessive growth of hair, known as hypertrichosis, can make horses uncomfortably warm and put them at risk of skin infections, especially as the days begin to get warm the following spring and the hair is not shedding naturally. While the drug pergolide and body clipping can help with hypertrichosis, many horses continue to produce thick coats that may affect their ability to thermoregulate.

The researchers suggested that blue light – one of the wavelengths found in natural sunlight – affects the horse’s natural circadian rhythms. Murphy said this affects the seasonal hormone regulations that affect hair growth. With the goal of helping owners better control the amount of “daylight” horses get, Murphy developed a photomask for horses—which projects a small beam of blue, wavelength light onto one eye. She said that aside from using the masks to manipulate the estrous cycles of mares, people have been using the masks on horses starting in mid-spring to help sport horses maintain a summer coat throughout the year.

“What blue light does is regulate melatonin,” Murphy said. “And melatonin is a hormone that mainly controls seasonal activity and a host of other hormones for horses – one of which is prolactin – which is responsible for hair loss. My work has shown previously that we can shed in horses at different times of the year.”

PPID study horses are great for hiding blue light

Amanda Adams, PhD, associate professor and equine immunologist at the University of Kentucky, in Lexington, read about Murphy’s equine sport-based work and wondered if blue light might also help horses affected by PPID. Along with her student, Ashton Miller, PhD, Adams teamed up with Murphy to study 18 PPID-positive senior horses of different breeds, all of whom live at the same research center near Lexington. None were treated with pergolide at the time of the study.

The team outfitted eight of the horses with blue light masks from mid-July to late October, and the other horses were not exposed to artificial lighting. The masks provided the horses with a total of 14.5 hours per day of blue light, including hours of natural sunlight. Those without masks only get about 10.5 hours of blue light through sunlight per day, Murphy said.

Murphy said average ACTH levels did not differ between the two groups of horses at the start of the study or at several time points in mid-October. There were also no differences in mean body weight, body temperature, heart rate, or respiratory rate between the groups.

However, the individual hairs of the masked horses — taken from behind the hip on seven separate days throughout the experiment — weighed less than the hairs of the control horses, Murphy said. She added that even though their coats were lighter, the horses still developed winter coats that were warm enough not to require covering the following winter.

“I was really excited by these results,” said Murphy. We have seen a decrease in the thickness and length of the hairs that have grown. The hair was finer, and had not grown out like a heavy coat by the end of the study. We care so much about these animals, and we really want to see their well-being improve with this condition.”

A larger and longer international study is now underway

The results confirm some of the stories Murphy has heard from owners who have already tried the masks on their PPID horses. These success stories, along with the encouraging results in this preliminary study, prompted Murphy to take a deeper look on a broader scale.

In December 2021, Murphy and her colleagues began a year-long study of 60 horses owned by a PPID client in Europe and North America who wore masks for a full year. “We are entering an exciting time now when horses that wear blue lights – if they are working for molt – will start to have a lighter coat than normal [due to PPID]. ”

the study, Effect of blue light therapy on plasma adrenocorticotropic hormone (ACTH) and hypertrichosis in horses with pituitary gland dysfunction. Pet endocrinology in January 2022.

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