A meta-analysis of the combined effect of housing and environmental enrichment characteristics on the behaviour and performance of pigs

To quantify the combined effect of housing conditions and environmental enrichment on the behaviour and performance of pigs, a meta-analysis was performed using information from 45 experiments in 42 published manuscripts. Multiple regression models were applied to evaluate the effects of space allowance per pig (k-value; m2/BW0.667), group size (n), floor characteristics (solid, partly, or totally slatted floor), bedding (presence or absence), and the number and presentation sequence of point-source objects (no object, one object, two simultaneous objects, two alternated objects, three or more simultaneous objects or three or more alternated objects) on the general activity, enrichment and object-directed exploratory behaviour, social behaviour, and productive performance. A non-linear relationship between space allowance per pig and time spent sitting and lying was found (P < 0.10 and P < 0.01 for the k-value and its quadratic term respectively). Total time spent in exploration increased with space allowance per pig when bedding was present (P < 0.01), and time spent exploring other pen items decreased with increasing space allowance per pig if no bedding was provided (P < 0.001). Total time spent in exploration increased with group size (P < 0.001). The lowest predicted total exploration time (least squares mean ± standard error) was found in the absence of bedding and point-source objects (13 ± 3%; P < 0.05), and the highest when bedding (18 ± 3%) or point-source objects (19 ± 3%) were present. Time exploring point-source objects was higher when different objects were provided (P < 0.001). Suspended (P < 0.05) and deformable (P < 0.05) enrichment items increased the time spent manipulating them. Time spent exploring point-source objects was predicted to be higher in the absence of slats and bedding (32 ± 6%; P < 0.05), and lower when bedding (8 ± 9%) or slats (12 ± 4%) were present. Time engaged in negative social behaviours decreased in the presence of point-source objects (P < 0.01), and increased with group size in the absence of bedding (P < 0.001). Time engaged in positive social behaviours tended to decrease in the presence of point-source objects (P < 0.10), and when space allowance per pig increased in the absence of bedding (P < 0.10). Slight trends towards lower FCR were predicted when point-source objects (P < 0.10) and bedding (P = 0.10) were present. This information can be utilised in the determination of the general effects of production systems on the welfare of pigs as well as in the development of new production systems.