Can artificial light enlighten pig welfare?

Current pig farming faces the challenge of improving animal welfare. The role of (artificial) light has been largely ignored in this debate, even though light is known to have a strong influence on pigs’ daily rhythms and productivity. The aim of this review was to explore the potential of artificial light to improve animal welfare in pig production. Most light-related research in pigs involves the photoperiod (=illumination duration) as a key parameter linked to health and (re)production. A light period of ≥16 hours, for example, increased feed intake, growth and health in young and growing pigs, compared to the legally required 8 hours/day. Other important light parameters, i.e. intensity (=brightness) and light spectrum (=colour), have been studied less. Those parameters, however, might play an important role in pig welfare via behavioural rhythmicity and affective state. In humans, low and high light intensities activate the circadian system and affect the sleep and wakefulness rhythm and light from various parts of the visible spectrum can influence behavioural rhythmicity and mood. Additionally, invisible (ultraviolet) light affects vitamin D synthesis in the skin for both pigs and humans. Vitamin D is essential to bone health, various physiological processes in the body and can affect mood and depression in humans, but its effect on pigs’ affective state is unknown. Those findings in human research and the anatomical and physiological similarities between pigs and humans suggest that those light parameters might be more important for pig welfare than currently anticipated. Present legal requirements for lighting conditions in pig farms are poorly supported by scientific evidence and are therefore likely to be sub-optimal. Improved use of light, supported by the use of novel light technology (i.e. LED), offers opportunities to simulate ‘natural light regimes’ and thereby stimulate natural biological processes and improve animal welfare in pig production.