Reactivity of growing rabbits under different housing systems

To evaluate the effect of housing system (bicellular cages vs collective pens) and, within collective systems, of pen size and stocking density on animal reactivity, a total of 456 rabbits was kept in pairs in bicellular cages or in large groups (20 to 54 animals) in collective cages of different sizes (small vs large) with wooden slatted floor and at two stocking densities (12 vs 16 rabbits/m2). The effects of the rearing system were assessed on rabbit reactivity to humans (tonic immobility test at 55 and 72 days of age) and against a new environment (open field test at 56 and 75 days of age). The reactivity of rabbits at the tonic immobility test was not affected by the age of the animals at the test, whereas at the open field test the younger rabbits spent less time in biting walls and edges of the enclosure (2.58 vs 6.33 sec; P<0.001) and showed a higher number of jumps (0.25 vs 0.01; P<0.01) and alerts (0.29 vs 0.05; P<0.01) than the older rabbits. With reference to the effect of the housing system, the percentage of rabbits that did not fall in immobility tended to be lower (6.2 vs 23.5%; P=0.09) and the amount of rabbits that rested in tonic immobility from 1 to 179 second tended to be higher (90 vs 73%; P=0.09) in the rabbits kept in bicellular cages than in those housed in collective cages. At the open field test, the rabbits reared in bicellular cages crossed more squares (47.5 vs 31.2, P<0.01) and moved more (58.3 vs 40.4 sec, P<0.01) than the rabbits in collective cages, whereas they stand in a vigilance position for a shorter time (38.7 vs 84.6 sec, P=0.04). Neither the cage size nor the stocking density in the collective pens significantly affected rabbit reactivity. In conclusion, the rabbits housed in bicellular cages showed a higher fear level against man but were more prone to exploration in a new environment in comparison with group-housed rabbits.