Enlightened pigs : Throwing light on pig welfare

Summary

The intensification of pig production systems in the last century, resulting in a shift from outdoor to indoor housing, has replaced natural daylight with artificial lighting. While Light Emitting Diodes (LED) offer advantages like energy efficiency and durability, their application in pig welfare research is still limited. Current EU regulations for pig housing focus on photoperiod (duration) and intensity (brightness) but neglect the light spectrum (colour). Moreover, scientific evidence supporting the proposed levels to improve pig welfare is limited. This thesis investigates how lighting conditions, in particular intensity and spectrum, affect the welfare of growing-finishing pigs. A review of the literature revealed that pigs exhibit preferences for specific light intensities and spectra, but results are inconsistent and vary across time. Photoperiod impacts feed intake, growth, and activity patterns, while light intensity influences behaviours such as resting and social interactions. However, studies often confound multiple light parameters, making it difficult to disentangle their individual effects. To address these limitations, experiments were conducted to assess the effects of light intensity, spectrum, and UVB light on pig behaviour, health, and growth. Light intensities from 45 to 968 lux were tested, including both uniform and gradient distributions. While behaviours such as exploration, play, and social interactions were monitored bi-weekly, no light treatment consistently outperformed another in terms of behaviour or health. Light intensity also had no clear effect on growth or carcass abnormalities, suggesting that pigs adapt to a range of intensities. Automated video analysis, using a YOLOv8-based model, was developed to study pig activity under different lighting conditions. This model effectively detected pigs and their postures, although challenges remained for sitting pigs. This tool revealed subtle differences in hourly activity patterns across light intensities, with high-intensity light reducing afternoon activity peaks, while medium intensity resulted in more pronounced activity peaks. The effects of four light spectra from 2 594 to 6 235 K were also examined with or without UVB. Behaviour, health, growth, and activity were assessed, and blood samples analysed for vitamin D and bone mineralisation. Results showed inconsistent effects of light spectrum on behaviour and activity. However, UVB increased vitamin D levels and reduced body and ear lesion severity and occasionally limited damaging behaviours. Light spectrum had no significant effects on growth or carcass abnormalities. These findings highlight the need for further research on this light parameter. This thesis has identified aspects of pig welfare potentially influenced by light, pinpointed the limitations of current knowledge on this topic, and contributed to our understanding of the role of light intensity, light spectrum, and UVB light on the welfare of growing-finishing pigs.