Blue light from individual light masks directed at a single eye advances the breeding season in mares

Summary Reasons for performing study Artificial lighting is commonly used to advance the breeding season in horses. Light masks have been developed that direct light at a single eye to inhibit the production of melatonin, the decoder of photoperiod for seasonally breeding animals. Objectives To investigate whether low‐intensity blue light from light masks was effective at advancing the breeding season in mares. Study design Controlled experiment. Methods Data on reproductive activity was collected from 3 groups of mares maintained on K entucky horse farms under various lighting conditions between 20 N ovember 2011 and 10 F ebruary 2012: 59 nonpregnant, healthy T horoughbred mares were used. On 1 D ecember 2011, G roup 1 (n = 16) was housed indoors under barn lighting (250 Lux) until 23.00 h daily. Group 2 (n = 25) wore light masks programmed to turn on from 16.30 h until 23.00 h daily and was maintained outdoors. Group 3 (n = 19) was maintained outdoors under the natural photoperiod as control. At 2‐week intervals, rectal ultrasound examinations were performed and blood was collected for progesterone analysis. Oestrous cyclicity was defined as the presence of follicles >20 mm diameter detected in conjunction with serum progesterone >1 ng/ml and confirmation of ovulation by transrectal ultrasound examination. Results On 10 F ebruary, the number of mares exhibiting oestrous cyclicity was 14/16 (87.5%) in G roup 1 ; 20/25 (80%) in G roup 2 ; and 4/19 (21%), in G roup 3 . Pairwise comparison of groups revealed no difference in the number of cycling mares between G roups 1 and 2 (χ 2 test, P = 0.3348) whereas differences were observed between G roups 1 and 3 (χ 2 test, P<0.0001) and G roups 2 and 3 (χ 2 test, P<0.0003). Conclusions Low‐intensity blue light to a single eye from a light mask is an effective alternative to maintenance of mares indoors under lights for advancing the breeding season. Mobile light therapy for horses could have economic benefits for the breeder by reducing the costs of maintaining mares indoors, and welfare benefits for horses by permitting outdoor maintenance.