A new way to advance the breeding season in mares is being developed following research into the use of light-emitting diodes (LEDs) to inhibit melatonin secretion.
Thoroughbred breeders aim to have foals born as soon as possible after the official birthday of January 1st (in the northern hemisphere.) This gives them a head start in size and maturity when competing against other horses in the same age group, both at sales and subsequently at the race track.
However, breeding early in the year is at odds with the horse's natural breeding season, which occurs some months later.
Artificial light is commonly used to advance the breeding season in mares. When an early foal is desired, breeders will put the mare "under lights" - keeping the barn lights on in the winter, to mimic the lengthening days that initiate the natural breeding season.
The hormone responsible for controlling this seasonal variation in response to change in day length is melatonin. It is secreted by the pineal gland in response to darkness.
Researchers at the University College Dublin's School of Agriculture and Food Science, have been examining the effect of different levels of blue light on melatonin production.
Four healthy 5-year-old TB mares took part in the study, which was conducted around the vernal (spring) equinox, so the mares were accustomed to equal 12 hour periods of light and darkness. For the duration of the study the mares were housed in a light-tight barn with artificial lighting timed to mimic the conditions outside .
The researchers used LEDs (emitting blue light of wavelength 468nm) set in a head mask to investigate the effect of blue light on melatonin secretion in the horse. (Blue light (465–485 nm) has been found to be the most efficient for inhibiting melatonin secretion in humans.)
Blood samples were collected through indwelling catheters at the end of hour-long periods of exposure to dark or to varying intensities of light. The light was directed at either both eyes or just one eye.
All samples, except the first, collected after exposure to “daylight”, occurred during the dark phase of the 24 h cycle.
The results showed that blue light inhibited the production of melatonin. The inhibitory effect occurred regardless of whether the light was administered to one or both eyes.
Melatonin levels were significantly lower after exposure to 10 lux, 50 lux, 100 lux as well as barn light, than they were after an hour of darkness. Melatonin levels after exposure to 3 lux were not significantly different from those recorded in darkness.
Lead researcher Dr Barbara Murphy, concludes that “melatonin inhibition can be achieved by exposing a single eye to low wavelength blue light.” She adds that “this is a novel finding with important implications for management of artificial lighting regimens in horses.”
“The light mask represents a safe cost-effective method of administering timed low-level light to a single eye so that mares can be maintained outdoors in their natural environment, avoiding the costs of indoor maintenance, while effectively advancing the onset of the breeding season to meet industry timelines.”
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