Effects of blue monochromatic light directed at one eye of pregnant horse mares on gestation, parturition and foal maturity.

• Blue LED light treatment during winter affected pregnancy outcome in horses. • Gestation was shorter in blue LED light-treated than in control pregnancies. • Height at birth was reduced in foals born to blue LED light-treated mares. • Hair length was reduced in foals born to blue LED light-treated mares. • Blue LED did not affect foal birth weight. Blue light directed at 1 eye advances the equine ovulatory season but may also advance foaling. In this study, effects of blue LED light on pregnancy outcome were assessed. A total of 20 mares with singleton pregnancies were studied over 2 consecutive years in a cross-over design. In 1 year, mares received an extended photoperiod using 50 lux of blue LED light (468 nm) directed at a single eye from 08:00 until 23:00 daily via head-worn light masks starting mid-December and in the other year remained untreated as controls. Gestation was shorter in blue LED light-treated than in control pregnancies (median 333.0 vs 338.5 days, P = 0.036). Foals born to blue LED light-treated mares had lower wither heights (median 103.0 vs 104.5 cm, P = 0.023), similar weights (median 55.8 vs 54.8 kg, P = 0.732) and took less time to stand after birth than control foals (median 35.0 vs 53.5 min, P = 0.036). Foals born to blue LED light-treated mares had reduced hair length compared to controls (median 12.0 vs 20.0 mm, P = 0.009) and hair regrowth in treated mares was reduced (P = 0.036). In conclusion, blue LED light directed at 1 eye advanced foaling and influenced height and hair coat but not weight in foals. [ABSTRACT FROM AUTHOR]