Mobile blue light therapy is as effective as stable lighting at advancing seasonal reproductive activity in mares

Artificial lighting is commonly used to advance the breeding season in horses. Recently, we developed light masks that direct low intensity (50 Lux) short wavelength light at a single eye to inhibit the production of melatonin, the decoder of photoperiod for seasonally breeding animals. In this study we investigate whether low intensity blue light (468 nm) from head-worn light masks was effective in advancing the breeding season in mares maintained outdoors under pasture conditions. Fifty nine non-pregnant, healthy Thoroughbred mares were maintained on a farm in Kentucky, USA at longitude W-84.4 and latitude N 38.1. On Nov 20th, the reproductive status of each mare was determined by ultrasound examination and progesterone analysis. On December 1st 2011, Group 1 (n1⁄416) was housed indoors under barn lighting (250 Lux) until 23:00 daily. Group 2 (n1⁄425) wore light masks programmed to turn on from 16:30 until 23:00 daily and was maintained outdoors. Group 3 (n1⁄419) was maintained outdoors under the natural photoperiod, as control. At 2week intervals, rectal ultrasound examinations were