Light environments for dairy cows : impact of light intensity, spectrum and uniformity

Sammanfattning: Light can be used as a management tool to increase milk yield in dairy cows and improve the working conditions for barn staff. It is known that a long day photoperiod, with 16 hours of light and 8 hours of darkness, can increase milk yield in an ongoing lactation. Modern LED lighting can be designed to emit specific wavelengths, opening up possibilities for discussing the most favorable type of light for dairy cows. This thesis investigated the role of light environment and the impact of light intensity, spectral composition and uniformity on dairy cows. In initial studies, a light lab with a controlled light environment and no external light was used. The response to red, blue, and white light of increasing intensity on pupil size was evaluated in five pregnant non-lactating cows. Red light did not constrict the pupil but the other light colors did, indicating that direct stimulation of ipRGCs may be required for a pupillary response to steady background light. A five-week study on 40 pregnant and lactating cows involving 16 hours of blue, red or white light in daytime and 8 hours of dim, white light at night did not show effects of light color during daytime on milk production. Plasma melatonin concentration was higher in dim night light than in daylight for all light treatments. To examine cow movements in light of different intensity, spectrum and uniformity, 12 pregnant, non-lactating cows were tested in an obstacle course in the light lab. A dark environment did not limit the cows’ ability to walk through the obstacle course, but they reduced walking speed when subjected to non-uniform, low-intensity red light, indicating the importance of avoiding non-uniform light in dairy barns. Quantification of light environments on four Swedish dairy farms, using a range of measuring methods, showed that the light environment differed between farms, but that light of low intensity and uniformity was commonly used. Light environment is important for dairy cows, as it can affect their physiology and behavior. The light environment can be more objectively described using multiple measuring methods.