Light masks on mares show potential as breeding tool

Dr Barbara Murphy with the Equilume therapeutic light mask.
Dr Barbara Murphy with the Equilume therapeutic light mask.

Mares may soon be wandering their pastures wearing light masks, following research which shows light therapy in the pasture is just as effective as that used in stables to stimulate breeding.

Blue-light therapy is showing considerable promise in horses, being able to inhibit melatonin levels in horses at lower levels than light from traditional bulbs.

Horses are long-day seasonal breeders, notes Dr Barbara Murphy, a lecturer in equine science with the School of Agriculture and Food Science at University College Dublin.

The natural reproductive period coincides with the light-filled days between May and September [in the northern hemisphere] , when the environment is optimal for the survival of offspring.

However, the universal northern hemisphere birthday for many horse breeds is January 1.

“This creates a demand for early foals in order to produce mature yearlings and two-year-old racehorses,” Murphy notes in the latest issue of Equine Disease Quarterly.

“Utilization of artificial light to advance the breeding season is common practice within the thoroughbred industry.

“Mares are maintained indoors under barn lighting until 11pm for eight to 10 weeks beginning around December 1. The artificially extended day length acts to inhibit the hormone melatonin and fools the mare’s reproductive system into activating earlier in the year.

“Historically, light from a 100-watt light bulb in a 12-foot by 12-foot stall has been used. This amount of illumination is loosely defined in the literature as ‘enough light to read a newspaper’.”

Recently, light in the blue light spectrum – 465- 485nm – has been found to facilitate more accurate and efficient levels of melatonin inhibition in other species.

In 2011, researchers at the university investigated the threshold level of blue light required to inhibit circulating concentrations of melatonin in the horse and found it to be within the range of 10 to 50 lux — lux being the standard international unit of illuminance.

“The average light intensity at eye level in a stall illuminated by a 100-watt light bulb is 250 lux. Of greater significance was that the level of melatonin inhibition achieved did not differ when light was administered to one or both eyes.”

Murphy said a second multi-institutional study was conducted to determine whether low-level light to a single eye from a head-worn light mask could advance the breeding season in mares maintained outdoors.

Fifty-nine non-pregnant, healthy thoroughbred mares were allocated to one of three groups.

On December 1, the first group of 16 was housed indoors in individual stalls under barn lighting of 250 lux until 11pm daily. Group 2, comprising 25 mares, wore light masks programmed to be on from 4.30pm to 11pm daily and lived outdoors as a herd.

The third group, comprising 19 mares, was kept outdoors under the natural photoperiod as a control. All mares were maintained on farms in Lexington, Kentucky.

At two-week intervals until mid-February, all mares received rectal ultrasound examinations and blood was collected for progesterone hormone analysis.

On February 10, the number of mares determined to have ovulated was 14 of the 16 (87.5 per cent) in Group 1; 20 of 25 (80 per cent) in Group 2; and 4 from 19 (21 per cent), in Group 3.

There was no statistical difference between Groups 1 and 2, indicating that mobile blue-light therapy from head-worn light masks is as effective at advancing seasonality as indoor barn lighting.

Studies are under way to investigate additional applications of mobile blue-light therapy in horses for the purposes of increasing foal birth weights in early foals and reducing the effects of jet lag in performance horses.

The light-mask technology will be available in 2013, Murphy said.


Gluck’s Equine Disease Quarterly is funded by underwriters at Lloyd’s, London, brokers and their Kentucky agents.

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