Effects of feeding level and the presence of a foraging substrate on the behaviour and stress physiological response of individually housed gilts

Abstract

The effects of feeding level (unrestricted, UR and restricted, R) and the presence of a foraging substrate (no substrate, NS and substrate, S; wood chips on the floor) on both the behaviour and stress physiological response were studied in a 2×2 factorial design. In three batches and two rooms, 96 sows were individually housed in 3.1 m 2 pens with 60% solid floor. Behaviour was scan-sampled in three 2 h periods between feeding times on 1 day in weeks 8–12. In addition, video recordings (24 h) in week 12 or 13 were scan-sampled for ‘standing’. Salivary cortisol (every 2 h during 24 h) was measured in week 11 and urinary catecholamines (adrenaline/creatinine and noradrenaline/creatinine ratios) were determined in morning-urine samples in weeks 2, 7 and 12 or 13. Feeding level had a significant effect on most of the behavioural elements observed. In general, R-animals stood more (pooled results of three periods: 31.3% versus 13.2%; P<0.001) and showed more visible oral behaviour (42.8% versus 23.6%; P<0.001) than UR-animals (in period 3 NS-animals only). This included more pen manipulation, floor manipulation, sham chewing and other oral behaviour (e.g. teeth grinding). With restricted feeding, NS-animals showed more visible oral behaviour than S-animals (periods 1 and 3). S-animals showed more floor (substrate) manipulation, whereas NS-animals showed more pen manipulation and sham chewing (in periods 1 and 3 R-animals only). In contrast to behaviour, stress physiological parameters were predominantly influenced by substrate. NS-animals had higher circadian salivary cortisol levels (24 h average: 2.54 ng/ml versus 0.97 ng/ml; P<0.01) and higher noradrenaline/creatinine ratios in weeks 7 (5.6 ng/mg versus 4.1 ng/mg; P<0.01) and 12 ( P<0.05). In week 2, NS-animals differed from S-animals, only with unrestricted feeding. No treatment effects were found on adrenaline/creatinine ratios, probably because animals were not exposed to acute stressors. Lower cortisol and noradrenaline levels could indicate a positive effect of substrate on welfare, but chewing on substrate may have any unknown physiological effects (e.g. dilution of saliva). In conclusion, behavioural results imply that a high feeding level can more effectively improve welfare of sows than the presence of wood chips on the floor. Stress physiological parameters, however, imply that the presence of wood chips can improve the welfare of sows to a certain extent, even when feed is offered ad libitum. Substrate manipulation may indicate an intrinsic need to express foraging or explorative behaviour.