Effects of light spectrum on pig behaviour, health and growth

Abstract

Pigs show preferences to display certain behaviours under specific light spectra. Moreover, adding UVB light to the spectrum might enhance pigs’ vitamin D status. Despite the potential, there are still gaps in understanding the broader effects of light spectrum on pig behaviour, health and growth due to the limited number of studies. Therefore, this study investigated how various light spectra, including exposure to UVB light, influence the behaviour, health and growth of growing-finishing pigs. An experiment with a split-plot design was conducted on a commercial farm, testing four different light spectra in plots (warm white; 2594 K, forest white; 4336 K, cool white; 6235 K, fluorescent tubes; 3787 K), and the addition of UVB light in subplots (UVB or non-UVB). Each light spectrum was tested on 112 pigs divided into two batches of eight pens each. Within each light spectrum, 28 pigs received additional UVB light. Pig behaviour was analysed every two weeks, both manually and using computer vision, while health was assessed weekly. Pigs were weighed at the start of the experiment and before transport to the slaughterhouse. During slaughter, abnormalities on carcasses were scored and blood samples were collected for analysis of vitamin D and bone modelling-related variables. Effects of light spectra on positive and negative social interactions, exploration and play behaviour were inconsistent over time and were mainly found in the first six weeks. Moreover, light spectrum had a varying impact on pig activity, depending on the week. From week 6 onwards, pigs exposed to fluorescent tubes and forest white light spent more time in active postures (i.e. standing and sitting) than other light spectra. However, light spectra had no effect on the distance moved by pigs. Additional UVB light reduced damaging behaviours in week 4 and reduced the severity of ear and lesions on the middle body section throughout the growing-finishing phase. Furthermore, pigs exposed to UVB light had a higher blood vitamin D level than pigs not exposed to UVB light, this had, however, no effect on bone modelling variables. None of the light treatments influenced carcass abnormalities or growth. Overall, results suggest that light spectrum seems to have limited effects on behaviour, health and growth of growing-finishing pigs kept in commercial conditions with limited space and a relatively barren environment. As this is the first study addressing effects of light spectrum on different aspects of pig welfare, further research is needed to corroborate these findings.