Illumination or guiding light during night hours in the resting area of AM-barns

It is a common practice to have full illumination day and night in AM-barns. It is however questioned whether cows prefer/need guiding light/darkness during night hours. The aim was to investigate if dairy cows actively choose light or dark area for resting during night hours. The study was conducted in an AM research barn with controlled traffic and 2 by-pass gates. The resting area of the barn was divided into 2 identical sections by screening. The study was divided into 3 periods. Period 1 with full lightning in both parts of the resting area. Period 2 and 3 with one half of the resting area with full lighting (app. 200 lux), while the other had guiding light (5-7 lux) from 23:00h to 05:00h. After 3 weeks the lighting in the two sections was reversed. The cows distributed equally in both sections of the resting area during the whole experiment and no effect of level of illumination on production parameters could be seen on herd level. However there are indications that some cows preferred the light or the dark side and followed the changes, but no relation between ranking order and choice of light was found.