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Most mares’ ovaries go into a quiet state, or “anoestrus”, in the autumn and do not become active again until the spring, when they resume the 21-day cycle of follicle ovulation and fertility.

In Flat racing, an early foal has great advantages. For a January birth many studs keep the stable lights on for part of the night in midwinter to mimic the arrival of spring, but this is costly.

Vets in Ireland and Kentucky wondered if the same effect could be achieved with individual lights for each mare. They took the left eye cup out of a specially designed hood and cut a hole in the right cup, lining the remainder with silver foil. They then attached a small blue LED light to the inside programmed to shine gently into the right eye for fixed periods.

A group of mares in Kentucky were kept at pasture during the day in winter, but brought in at night. Their daylight hours were extended from 1 December with overhead lights in the stables, from 4.30pm to 11pm.

A second group lived out all the time, but on 1 December wore the hoods and received low-level blue light from the LED into the right eye from 4.30pm to 11pm. A third group lived out all the time through winter and received no artificial light exposure.

Ovarian activity was monitored and, as expected, the latter group of mares remained in anoestrus throughout January. The mares given extra daylight in their stables started cycling early and were in full swing in mid-January.

The mares living outdoors with the battery-operated light-emitting hoods also came into season early.

This method of extending daylight was just as successful as the stable light method — and far cheaper.

This article was first published in Horse & Hound magazine (18 September 2014)

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