Budget time of growing rabbits housed in bicellular cages or collective pens at two ages

The present study aimed at assessing differences of budget time at 52 and 73 d in growing rabbits (456) housed in conventional bicellular cages (0.112 m2; 2 rabbits/cage) or open-top collective pens (20-54 rabbits/pen). The effect of pen size (small, 1.68 m2, vs. large, 3.36 m2) and stocking density (12 vs. 16 rabbits/m2) in collective pens was also evaluated. The data were firstly analysed by a mixed procedure with housing system (bicellular cages vs. collective pens), age and their interaction as fixed effects, and time of the day as random effect. The data of collective pens were then used to test the effect of pen size, stocking density, age and their interactions as fixed effects and time as random effect. The rabbits spent less time in feeding (7.76% vs. 10.9%) and allo-grooming (0.65% vs. 1.58%) and more time in moving (0.81% vs. 0.35%) and resting (82.1% vs. 77.7%) in collective pens than in bicellular cages (P<0.01); besides, rabbits in collective pens exhibited running, rearing and hopping and did not show stereotypic behaviours. Significant interactions (P<0.001) were measured between housing system and age: from 52 to 73 d feeding time decreased only in rabbits in collective pens; time of allo-grooming increased and time of moving and sniffing decreased only in rabbits in bicellular cages; the reduction of resting time with stretched body was more pronounced in bicellular cages (12.7% to 0.87%) than in collective pens (9.32% to 3.61%). In collective systems, both pen size and stocking density had weak effects. Within collective systems, when the age increased, rabbits spent more time self-grooming, allo-grooming, sniffing, and running, exhibited more hops and reduced feeding and resting time (0.05<P<0.001). During resting, the stretched position was preferred (8.37% to 3.24%) by younger than older rabbits. Some significant interactions between stocking density and age (P<0.01) were measured: at 52 d feeding time was lower in pens at 12 rabbits/m2 compared to those at 16 rabbits/m2 (7.19% vs. 9.49%), whereas differences disappeared at 73 d (6.60% vs. 6.35%); at 52 d, self-grooming (4.67%) and allo-grooming times (0.33%) were similar while they differed at 73 d of age (7.81% vs. 6.55% and 0.35% vs. 1.11%, respectively). In conclusions, rabbits in collective pens displayed a more complete behavioural pattern, despite resting more, than rabbits in bicellular cages. Within collective systems, variations in pen size and stocking density exerted only weak effects on a small number of behavioural traits.