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The Effects of Coloured LED Light on Behaviour and Physiology in Healthy Horses

The use of colour light therapy to treat diseases and disorders in animals is increasingly common but only very little research has been conducted on the effects of illumination with coloured light. The present study examined to which extent coloured light causes behavioural and physiological responses in horses. Red , green, blue and yellow as well as white as a control colour were tested in 20 healthy stallions of the breed Freiberger. Coloured light was applied on five consecutive days in randomised order for 15 min each in a LED light illuminated box stall. Behaviour was observed during illumination, salivary cortisol levels were measured immediately thereafter. Elimination, activity, heart rate and temperature parameters were recorded before, during and after illumination. Results showed that "Drinking" occurred more often at yellow and body core temperature was higher at red and blue and lower at green and yellow, whereas body surface temperature was tendentially increased at all colours compared to the control white. For the majority of parameters, however, no effects were found and discovered effects often did not correspond to expectations deriving from principles of colour light therapy. A general effect of illumination, regardless of the colour, was further demonstrated for activity, heart rate and heart rate variability and absolute values of physiological and behavioural parameters indicated that the illumination with coloured light did not constitute a stressor but rather had a becalming effect on horses.