Effects of light intensity on space use and pen fouling in growing-finishing pigs

Correct use of functional areas intended for resting, defecating and urinating limits environmental emissions and supports pig health and welfare. The role of light intensity in guiding pigs to properly use functional areas has been under considered so far, although there are indications that pigs prefer to rest in dimmer areas and defecate in brighter areas. We investigated how space use and pen fouling are affected by four different light treatments, consisting of a low, medium and high light intensity with a homogeneous distribution across the pen (averaging 46, 203 and 988 lux, respectively) and a spatial gradient with an intensity ranging from 72 lux in the feeding area to 331 lux in the dunging area. We studied 2 batches of commercial growing-finishing pigs that were subjected to the four light treatments applied in four separate rooms (n=8 pens per room per batch, with 7 pigs per pen). Pen fouling and space use were recorded on a weekly basis during 12 weeks. Preliminary results of the fi rst batch were analysed with mixed models including light intensity and week of observation. Repeated observations on the same pens were taken into account by including a repeated effect of sampling hour and observation week. Results indicate that fouling with faeces and urine of the resting and feeding area increased with age (p<0.0001) but no effect of light intensity was present. On average, the percentage of fl oor area covered in faeces and wets spots was 5.6±0.2% and 37.2±1.0% respectively (mean±SEM). Concerning space use, a 24-hour period was analysed in both week 6 and 10 of the finishing phase, using instantaneous scan sampling with 1h-intervals. Preliminary results indicate that light intensity did not affect the occurrence of lying in the dunging and feeding area, but lying in the dunging area significantly increased from week 6 to week 10 (24.0±0.01 vs. 27.9±0.01% of pigs per pen per sampling hour, p<0.001). This may be caused by avoidance of increasingly fouled pen areas or changed preferences towards a cooler microclimate within the pen, as the upper critical limit for heat stress lowers with increasing body weight. The average percentage of pigs lying in the resting area was higher (p<0.05) for the medium intensity (39.1±0.01%) than for the low intensity (27.2±0.01%) and spatial gradient (27.8±0.01%). This points towards improved space use under light conditions of medium intensity, however this can only be verifi ed after collecting data from batch 2