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

Blue light directed at one eye advances the equine ovulatory season but can also advance foaling. In this study, effects of blue LED light on pregnancy outcome were assessed. Twenty mares with singleton pregnancies were studied over two consecutive years in a cross-over design. In one 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 (333.2+/- 1.0 days, +/- SEM) than in control pregnancies (337.9+/-1.8 days, p<0.05). Colostral IgG content was lower in treated than in control pregnancies (p<0.05) but was adequate to ensure sufficient IgG transfer to newborn foals with a single exception. Foals born to blue LED light-treated mares had lower wither heights (102.5+/-1.1 vs. 105.2+/-1.0 cm, p<0.01), similar weights (55.0+/-1.3 vs. 55.5+/-1.1 kg) and took less time to stand after birth than control foals (39+/-3 vs. 56+/-4 min, p<0.05). The neutrophil/lymphocyte ratio, was higher in foals born to blue LED light-treated mares than controls (3.2+/-0.2 vs. 2.7+/-0.2; p<0.05). Foals born to blue LED light-treated mares had reduced hair length compared to controls (13.1+/-0.8 vs. 20.9+/-0.1 mm; p<0.001) and hair regrowth in treated mares was reduced (p<0.05). Maternal plasma prolactin concentration was increased in treated mares (p=0.05) and peaked at foaling (p<0.001). In conclusion, blue LED light directed at one eye advanced foaling and influenced height, hair coat and maturity in foals.