Development of Foals Until One Year of Age When the Dam was Exposed to Blue Monochromatic Light Directed at One Eye During Late Pregnancy.

In horses, blue LED light directed at one eye of pregnant mares shortens gestation length and results in the birth of foals with lower wither heights, similar weight and reduced hair length compared to controls. In this study, we have therefore analysed postnatal development of foals born to either blue LED light-treated (n = 20) or control mares (n = 20). Size, weight and hair coat changes were determined for 1 year and heart rate, heart rate variability (HRV) and selected haematology parameters for 1 month. Haematocrit decreased (P < .001) and leukocyte and lymphocyte counts increased (P < .001) but none of the parameters differed between groups. Heart rate (P < .001) and HRV (P < .01) increased until day 6 but did not differ between groups, indicating that foals born to blue LED light-treated mares were mature and healthy. The guard hair was shorter in foals born to treated mares compared to control foals at birth (P < .001) but no differences in hair coat length were observed beyond the age of 2 months. At birth and 6 days thereafter, wither height (P < .01) and elbow to carpus distance (P < .05) of control foals were increased relative to foals born to blue LED light-treated mares. Height differences decreased over time and and for elbow-to-carpus distance there was a time x group interaction (P < .005) In conclusion, blue LED light treatment of pregnant mares is without detrimental effects on postnatal foal growth and development.