Blue light from light-emitting diodes directed at a single eye elicits a dose-dependent suppression of melatonin in horses.
Abstract: The production of melatonin during night-time hours decodes day length for seasonally breeding animals. The use of artificial light to advance the breeding season in mares is common practice within the equine industry. Four healthy Thoroughbred mares were used to evaluate the minimum intensity of light required to inhibit serum melatonin. Mares were fitted with indwelling jugular catheters and using a crossover design blood samples were collected following 1h exposure to light (barn lighting approximately 200 lux), dark (<0.1 lux), and 3, 10, 50, and 100 lux intensities. The light source was a light-emitting diode (LED; 468 nm) directed at either a single eye or both eyes. All treatments, except the sample collected after 1 h exposure to light, occurred during the dark phase of the 24 h cycle. Serum melatonin levels were determined by radioimmunoassay. Two-way repeated measures ANOVA revealed that there was no difference between the level of melatonin inhibition achieved when light was administered to one or two eyes (P = 0.7028). One-way ANOVA of melatonin levels at light intensities of 10, 50 and 100 lux were significantly different to dark (P 0.05) intensities. There was no difference between melatonin levels at 3 lux (P > 0.05) and dark intensities. The threshold level of low wavelength light required to inhibit melatonin production in the horse lies between 3 and 10 lux. Melatonin inhibition can be achieved by exposing a single eye to low wavelength blue light. This is a novel finding with important implications for management of artificial lighting regimens in horses.
Copyright © 2012 Elsevier Ltd. All rights reserved.
Publication Date: 2012-10-15 PubMed ID: 23079244DOI: 10.1016/j.tvjl.2012.09.003Google Scholar: Lookup
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- Clinical Trial
- Journal Article
- Research Support
- Non-U.S. Gov't
Summary
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This research paper explains an experiment conducted on horses to measure the impact of blue LED light on melatonin production. The study found that blue light, even when directed at just one eye, could suppress production of melatonin, a hormone responsible for regulating sleep and wakefulness, especially at certain intensities (between 3 and 10 lux).
Experimental Setup
- The scientists tested this out by running the experiment on four healthy Thoroughbred mares.
- These horses were fitted with jugular catheters and were positioned in varying lighting conditions ranging from complete darkness to light exposure at different intensities (3, 10, 50, and 100 lux).
- All procedures and treatments, except one where the horses were exposed to light for an hour, were performed during the dark phase of a 24-hour cycle.
- Blood samples were collected from the horses after these exposure periods and serum melatonin levels were evaluated using a technique referred to as radioimmunoassay.
Findings
- The results indicated that there wasn’t a significant difference in melatonin suppression levels when light was exposed to one eye versus two eyes.
- When the light’s intensity was at 10, 50, and 100 lux, the melatonin levels were significantly lower than that in complete darkness.
- However, there was no significant difference in melatonin levels between complete darkness and an intensity of 3 lux. Therefore, the researchers concluded that the threshold for blue light exposure needed to suppress melatonin production in horses falls somewhere between 3 and 10 lux.
Implication and Significance
- This study’s findings have important implications for managing artificial lighting regimens in horses, particularly in the equine industry where artificial light is used to manipulate the breeding cycle.
- The prospect that melatonin suppression can be achieved by exposing only a single eye broadens our understanding of how seasonally breeding animals decode day length and enable advanced management strategies.
Cite This Article
APA
Walsh CM, Prendergast RL, Sheridan JT, Murphy BA.
(2012).
Blue light from light-emitting diodes directed at a single eye elicits a dose-dependent suppression of melatonin in horses.
Vet J, 196(2), 231-235.
https://doi.org/10.1016/j.tvjl.2012.09.003 Publication
Researcher Affiliations
- School of Agriculture and Food Science, University College Dublin, Belfield, Dublin 4, Ireland.
MeSH Terms
- Animals
- Color
- Cross-Over Studies
- Female
- Horses / physiology
- Light
- Melatonin / genetics
- Melatonin / metabolism
- Reproduction / physiology
- Reproduction / radiation effects
- Seasons
Citations
This article has been cited 14 times.- Collery A, Browne JA, O'Brien C, Sheridan JT, Murphy BA. Optimised Stable Lighting Strengthens Circadian Clock Gene Rhythmicity in Equine Hair Follicles. Animals (Basel) 2023 Jul 17;13(14).
- Contreras-Correa ZE, Messman RD, Swanson RM, Lemley CO. Melatonin in Health and Disease: A Perspective for Livestock Production. Biomolecules 2023 Mar 7;13(3).
- Kim S, Jung H, Murphy BA, Yoon M. Efficiency of Equilume light mask on the resumption of early estrous cyclicity and ovulation in Thoroughbred mares. J Anim Sci Technol 2022 Jan;64(1):1-9.
- Sun W, Yan J, Wu J, Ma H. Efficacy and Safety of Light Therapy as a Home Treatment for Motor and Non-Motor Symptoms of Parkinson Disease: A Meta-Analysis. Med Sci Monit 2022 Jan 7;28:e935074.
- O'Brien C, Darcy-Dunne MR, Murphy BA. The effects of extended photoperiod and warmth on hair growth in ponies and horses at different times of year. PLoS One 2020;15(1):e0227115.
- Wakefield A, Broyles M, Stone EL, Jones G, Harris S. Experimentally comparing the attractiveness of domestic lights to insects: Do LEDs attract fewer insects than conventional light types?. Ecol Evol 2016 Nov;6(22):8028-8036.
- Guan D, Luo N, Tan X, Zhao Z, Huang Y, Na R, Zhang J, Zhao Y. Scanning of selection signature provides a glimpse into important economic traits in goats (Capra hircus). Sci Rep 2016 Oct 31;6:36372.
- Gao ML, Deng WL, Huang N, Wang YY, Lei XL, Xu ZQ, Hu DN, Cai JQ, Lu F, Jin ZB. Upregulation of GADD45α in light-damaged retinal pigment epithelial cells. Cell Death Discov 2016;2:16013.
- Akhtar MF, Swelum AA, Wang C. Effect of Monochromatic Red, Blue, and White Light on Reproductive Hormones of Male Donkeys During the Non-Breeding Season. Animals (Basel) 2026 Feb 4;16(3).
- Parmantier S, Kyriazopoulou P, McClendon M, Adams A, Murphy BA. Influence of Extended Photoperiod Using Blue Light Masks on Hypertrichosis, Coat Condition and General Health Parameters in Horses with Pituitary Pars Intermedia Dysfunction. Animals (Basel) 2025 Oct 5;15(19).
- Greening L, Harkin E, Kyriazopoulou P, Heppelthwaite Z, Aragona F, Browne JA, Hemmings A, Williams JM, Murphy BA. Influence of lighting on sleep behaviour, circadian rhythm and spontaneous blink rate in stabled riding school horses (Equus caballus). PLoS One 2025;20(6):e0326567.
- Ishimaru M, Kume K, Murase H, Sato F, Matsui A, Ohmura H, Taya K. Effect of birth month on endocrine function in Thoroughbred foals born in Hokkaido, the northern part of Japan. J Vet Med Sci 2025 Jul 7;87(7):804-815.
- Farag HI, Murphy BA, Templeman JR, Hanlon C, Joshua J, Koch TG, Niel L, Shoveller AK, Bedecarrats GY, Ellison A, Wilcockson D, Martino TA. One Health: Circadian Medicine Benefits Both Non-human Animals and Humans Alike. J Biol Rhythms 2024 Jun;39(3):237-269.
- Gáspárdy A, Gallagher G, Bartha B, Haaland H, Fekete SG. The Effect of Supplemental Lighting during the Late Gestation Period on Post-Partum Mechanical Properties of Mare and Foal Guard Hair. Vet Sci 2024 Jan 22;11(1).
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